Embed Size (px)
Citation preview
1
PDF Copy of MSc-thesis:
Rikke Mørck Nielsen, 2006
Aldersbestemmelse og populations dynamik hos Europæisk hare (Lepus europaeus) i Danmark
(Age determination and population dynamics of European hare (Lepus europaeus) in Denmark)
Internal supervisor: Gösta Nachman ([email protected]) Dept. Of Population Biology, Univ. Copenhagen. Universitetsparken 15, DK-2100 Copenhagen East External supervisor: Tommy Asferg ([email protected]) National Environmental Research Institute, Aarhus University, Dept. Wildlife Ecology and Biodiversity. Grenåvej 14, DK-8210 Rønde, Denmark
*R. M. Nielsen, present (November 2009) address: Skov- og Naturstyrelsen Midtjylland, Bjørnkærvej 18, DK-7540 Haderup, Denmark Tel. +45 25276365 E-mail: [email protected]
The thesis is comprised by a synopsis in Danish and two manuscripts in English
2
Aldersbestemmelse og populations dynamik hos Europæisk hare (Lepus europaeus) i Danmark
Specialerapport af
Rikke Mørck Nielsen 2006
Intern vejleder Gösta Nachman
Afdeling for populationsbiologi, Københavns Universitet
Ekstern vejleder Tommy Asferg, Danmarks Miljøundersøgelser
3
Forord
Dette speciale er skrevet på afdelingen for populationsbiologi på Københavns Universitet, Biologisk
Institut. Det er lavet med ekstern tilknytning til Danmarks Miljøundersøgelser (DMU) afdeling for
vildtbiologi og biodiversitet. Specialet er tredelt. Første del er skrevet på dansk. Denne del
indeholder en introduktion til den europæiske hares levevis og jagthistorie i Danmark, med fokus på
seneste relevante forskning inden for emnet. En kort gennemgang af populations dynamiske emner,
som life- og fekunditets tables. En oversigt over indsamlet materiale, samt teoretisk baggrund for
anvendte metoder. Herefter følger to separate artikeludkast, skrevet på engelsk.
Manuskript I : ESTIMATION OF AGE IN EUROPEAN BROWN HARES (Lepus europaeus),
BASED ON PERIOSTEAL GROWTH LINES.
Med hjælp fra Tandlægeskolen I Aarhus lykkedes det at få fremstillet tyndsnit af afkalkede
mandibler. Ud fra disse snit blev alle indsamlede harer, samt reference materiale med kendt alder,
aldersbestemt. I artiklen er der lagt vægt på validering af metoden, samt sammenligning med
resultater fra tidligere undersøgelser.
Manuskript II : POPULATION DYNAMICS OF EUROPEAN HARE (lepus europaeus) IN 11
DANISH LOCATIONS.
I denne artikel bliver forskelle i alder, længde, vægt og reproduktion for de 11 udvalgte lokaliteter
undersøgt og kommenteret. Der opstilles Life table for hver lokalitet og de stadie specifikke
overlevelses rater udregnet. Opnåede resultater sammenlignes med relevant litteratur og
kommenteres. Derudover opstilles der forklarende modeller for harernes reproduktive succes og den
stadie specifikke overlevelse. De opstillede modeller vidste sig desværre at være uden den store
forklarende værdi. Men med udgangspunkt i opnåede resultater, diskuteres tidligere studiers.
I forbindelse med mit speciale er der en række personer som jeg skylder tak:
Danmarks Miljøundersøgelser for finansiering. Gösta Nachman og Tommy Asferg for kyndig
vejledning. Trine-Lee Wincentz Jensen for gennemlæsning af manuskripter og for altid at tage sig
tid til, en til tider forvirret specialestuderende. Jette Barlach Og Sussi Madsen fra Århus
tandlægeskole for hjælpsomhed og godt udført arbejde i laboratoriet. Kontaktpersoner fra hver
lokalitet, som beredvilligt har svaret på alle mine spørgsmål. Kim Aaen for hjælp til fotografering af
4
hare-knogler. Pernille Maj Svendsen for korrekturlæsning af manuskripter. Jørn Pagh Berthelsen for
hare-ture i felten hhv. i Himmerland og på øen Hjelm. Min mor og far, samt resten af familien
Mørck Nielsen for non-stop økonomisk og moralsk opbakning i forbindelse med min uddannelse.
GOD LÆSELYST
Rikke Mørck Nielsen
5
INDHOLDSFORTEGNELSE
Forord...................................................................................................................................................3
INDHOLDSFORTEGNELSE.................................................................................................5
INTRODUKTION ......................................................................................................................7
Baggrund for speciale ..................................................................................................................7
DEN EUROPÆISKE BRUNE HARE ........................................................................................7
Taksonomi og udbredelse af Europæisk brun hare, Lepus europaeus..............................7
Habitat- og fødevalg...............................................................................................................8
Reproduktion og yngelpleje..................................................................................................9
Predation og sygdom............................................................................................................10
Harejagt i Danmark .............................................................................................................10
Faktorer der påvirker harebestanden................................................................................11
POPULATIONSDYNAMIK.....................................................................................................12
Opstilling af life table...........................................................................................................14
Opstilling af fekunditets table.............................................................................................15
Anvendelse af life- og fekunditets table..............................................................................15
BESKRIVELSE AF STUDIEOMRÅDER OG INDSAMLET MATERIALE.........................16
METODER TIL ALDERSBESTEMMELSE AF HARER.......................................................17
Visuel bedømmelse af vækstknuder...................................................................................17
Øjenlinse vægt......................................................................................................................18
Tilvækstlinier i underkæben...............................................................................................18
REFERENCER ..........................................................................................................................20
TABELLER ...............................................................................................................................25
FIGUR FORKLARINGER........................................................................................................29
FIGURER...................................................................................................................................30
MANUSKRIPT I..................................................................................................................42
ESTIMATION OF AGE IN EUROPEAN BROWN HARES (Lepus europaeus), BASED ON
PERIOSTEAL GROWTH LINES.............................................................................................42
Appendix ...................................................................................................................................52
MANUSKRIPT II ................................................................................................................53
6
POPULATIONS DYNAMICS OF EUROPEAN HARE (Lepus europaeus) IN 11 DANSIH
LOCATIONS. ............................................................................................................................53
Appendix 1................................................................................................................................69
Appendix 2................................................................................................................................83
Appendix 3................................................................................................................................84
7
INTRODUKTION
Baggrund for speciale
Dette speciale er del af et større markvildtprojekt igangsat af Danmarks Miljøundersøgelser (NERI)
i 2002. Markvildtprojektet som er et delprojekt under forskningsprogrammet Vildt og Landskab
(www.vildtoglandskab.dk) har til formål at udpege de primære årsager til den nedgang i hare- og
agerhønsepopulationer, der igennem de sidste 4 årtier er observeret i Danmark. Resultater fra
markvildtprojektet vil blive brugt i fremtidig forvaltning af de to arter. Formålet med dette speciale
er (i) at bestemme og beskrive europæisk hares aldersfordeling og reproduktionssucces (ii) at
undersøge effekten på overlevelsesrater og reproduktion i forhold til arealanvendelse,
trafikintensitet og predation mellem forskellige lokaliteter. Rådata for reproduktions-succes er
indsamlet af Trine-Lee Wincentz Jensen og venligst udlånt til behandling i dette speciale.
DEN EUROPÆISKE BRUNE HARE
Taksonomi og udbredelse af Europæisk brun hare, Lepus europaeus Europæisk brun hare tilhører familien Laporidae (tabel 1), som ud over harerne også omfatter alle
kanin-arter. Til slægten Lepus hører i alt 29 arter. Foruden Europæisk brun hare omfatter slægten
bl.a. arter som sneskoharen (Lepus americanus) og sneharen (Lepus timidus). I Danmark er
Europæisk brun hare eneste repræsentant fra slægten Lepus. Den Europæiske hares
udbredelsesområde strækker sig fra Vesteuropa til det Sibiriske lavland og sydøst Asien (Iran).
Arten findes i størstedelen af Europa, med undtagelse af Nordskandinavien, de nordlige egne af
Rusland, den Iberiske halvø, syd for Cantabria, samt de fleste af middelhavsøerne (figur 1,
Mitchell-Jones et al., 1999). Ud over de nævnte områder er den Europæiske hare udsat i bl.a.
Australien, New Zealand, USA og Argentina. I Danmark menes den Europæiske hare at være
indvandret for 3000-3500 år siden. I denne periode blev der fældet store arealer i Danmark og
derved frembragt den Europæiske hares foretrukne terræn, åben opdyrket land (Kleist, 1995). I dag
er haren udbredt til stort set hele landet, kun fraværende enkelte steder. Betegnelsen hare vil i det
følgende referere til Europæisk brun hare.
8
Habitat- og fødevalg
Harens foretrukne levested er det varierede landbrugsland, hvor levende hegn og andre småbiotoper
adskiller de opdyrkede marker (Tapper & Barnes, 1986). Her finder haren mulighed for både
fouragering i skumrings- og nattetimerne, samt dække i dagstimerne. Haren er primært aktiv i
skumrings- og nattetimerne, hvor den fouragerer alene eller i små grupper. Fourageringen finder
ofte sted på andre arealer end hvor haren opholder sig om dagen (Tapper & Barnes, 1896). Harens
fødevalg er alsidigt og tilpasset årstidens plantedække. Harens fødevalg spænder således fra et bredt
udvalg af urter, markafgrøder og græsser, til bark, kviste og skud i strenge vintre (Rödel et al.,
2003). Tidligere studier udført af Danmarks Miljøundersøgelser på Kalø har vist at vinterhvede og
græsmarker med kløverudlæg, her var harens foretrukne fourageringsplads (Hansen et al., 1989). Et
studium udført på en harepopulation nær Odense Universitet viste ligeledes at vinterhvede og
diverse græsser udgjorde den vigtigste fødekilde for harerne (Hansen et al., 1990). Samme
undersøgelse viste at haren fortrinsvis æder kornafgrøder, roer, ærter og raps fra fremspring til
buskningsstadiet, mens mælkebøtte og kløver ædes i alle vækststadier. En engelsk undersøgelse har
vidst at hares præference for kortsorter falder når kornet når ind i strækningsstadiet (Tapper &
Barnes, 1986). Størstedelen af harens føde består af markafgrøder, men det ser ud til at den
fortrækker urter og vilde græsser, når disse er til rådighed (Reichlin et al., 2006). Undersøgelser fra
England har vidst at harer der lever i forbindelse med græsarealer ikke kun levere kortere men også
vejer mindre og er fysisk dårligere tilstand end harer der lever på opdyrkede arealer (Smith et al.,
2005). Samme undersøgelse vidste at der ingen forskel var på fødekvaliteten imellem de to
habitater, den observerede forskel må altså skyldes andre parametre.
Haren er psudo-drøvtrygger, det vil sige at harens føde skal passere tarmsystemet to gange for
optimal udnyttelse af føden. I stedet for at gylpe føden op igen som de almindelige drøvtyggere,
æder haren sine ekskrementer når den har passeret tarmsystemet første gang (Kleist 1995). Haren
tilbringer, som andre drøvtyggere, mange timer med at fordøje sin føde. Dette sker i dagtimerne,
hvor haren sidder i sit sæde, en fordybning i vegetationen (Jensen, 1993). Harens sæde er ofte
placeret i forbindelse med dække, så som buske eller anden høj vegetation, og med udsigt ud over
det omgivende landskab (Angelici et al., 1999). Dette optimere harens muligheder for at undslippe
eventuelle angreb fra rovdyr. Hvert sæde benyttes sjældent mere en 3-4 dage i træk (Angelici et al.,
1999). Studier fra Danmarks Miljøundersøgelser har vist at haren ofte er meget stedfast i forhold til
fourageringspladser. (personlig kommentar Trine Lee Wincentz Jensen). Dette støttes af tidligere
9
studier, hvor harer trods dårlig føde kvalitet, ofte forbliver i deres normale home-range i stedet for
at søge føde andre steder (Rühe & Hohmann, 2004). Dette kan om sommeren sandsynligvis
medføre nedsat reproduktion. Studier har bestemt harens home-range til 14-40 hektar (Abildgård et
al., 1972; Broekhuizen & Maaskamp, 1979).
Reproduktion og yngelpleje
Harens ynglesæson i Danmark strækker sig over det meste af året, fra januar til oktober (Hansen,
1991). I løbet af en ynglesæson kan en enkelt hun sætte helt op til fire kuld (Hansen, 1991). Antallet
af kuld kan være positivt korreleret med størrelse og kropsvægt (Frylestam, unpubl.). Haren er
polygam og hunharen (sætteren) kan i det tidlige forår, hvor vegetation stadig er kort, ofte ses ifølge
med flere hanner (ramlere). Sætteren er drægtig i 42- 43 dage og kan befrugtes med næste kuld
inden den har født det første, et fænomen der kaldes superfoetation (Muus, 1991). Kuldstørrelsen
varierer normalt fra 1 til 5 killinger per kuld. Studier fra Danmark har vist at det andet og det tredje
kuld i gennemsnit er større end det første og fjerde kuld (Hansen, 1992). Hansen (1991) bestemte
den gennemsnitlige produktion af killinger til mellem 6,4-8,8 killinger per hun per år. Dette tal er
lavt sammenlignet med studier fra Frankrig, der fandt den årlige produktion per hun til mellem 12
og 15 killinger (Marboutin et al., 2003). Den observerede forskel kan skyldes Frankrigs milde klima
og dermed længere yngle sæson end i Danmark.
Harens killinger fødes med pels og åbne øjne. Kort efter fødslen forlader sætteren killingerne og
herefter dies killingerne kun en enkelt gang per døgn. Diegivningen finder ofte sted omkring en
time efter solnedgang i umiddelbar nærhed af fødestedet. Sætterens mælk er blandt de mest
næringsrige i pattedyregruppen, med et indhold af 23 % fedt og 17 % protein. Killingerne dier til de
er en måned gamle, herefter klarer killingerne sig selv (Muus, 1991). Ungdyrene yngler som oftest
først året efter deres fødsel, men det forekommer at enkelte harer reproducerer sig, i samme
yngelsæson, som de er født (Marboutin et al., 2003). Killinge-dødeligheden er ofte høj og er i
studier fra forskellige europæiske lande bestemt til mellem 50 og 86 % (Pepin, 1989; Marboutin et
al, 2003; Smith et al, 2005) (tabel 2). Sammenlignet med 41-66 % dødelighed hos de voksne harer
(Abildsgård et al, 1972; Frylestam, 1980; Broekhuizen, 1982; Marboutin and Peroux, 1995) (tabel
2).
10
Predation og sygdom
I Danmark findes der en lang række af rovdyr, der prederer på haren, i særdeleshed harekillingerne.
Det menes, at ræven står for størstedelen af predationen, men også mår, kat, kragefugle og en række
rovfugle tager harekillinger. Forsøg med modellering af hare-population, har vidst at ræve kan
nedlægge helt op til 76-100 % af den årlige produktion af harer (Reynolds & Tapper, 1995).
Faktiske studier fra Sverige tyder dog på at de faktiske tal er noget mindre (Erlinge et al., 1984)
Studier fra Danmark har påvist predation af ræve som den vigtigste faktor til nedgangen i den
danske harebestand (Schmidt et al., 2004). I studie fra Polen har man fundet at op til 53 %
vintermortalitet hos harer kan tilskrives ræve-predation (Goszczynski & Wasilewski, 1992).
Når der forekommer sygdom i en harepopulation er det ofte med dødelig udgang for de smittede
individer. Akut haredød (AHD), også kaldet European Brown Hare Syndrome (EBHS) er en virus,
som medfører forandringer i levervæv, samt forstyrrelser i nervesystemet. Inficerede individer dør
ofte inden for få timer efter de er blevet smittet, Såfremt harerne lever længere med sygdommen
udvikles gulsot. Af bakterielle sygdomme findes harepest (tularæmi), pseudotuberkulose,
byldesyge, brucellose og lungebetændelse, alle sygdomme som med jævne mellemrum ses i danske
harerpopulationer. Coccidioose og Toxoplasmose er encellede snyltere, som begge kan findes hos
danske harer. Voksne og ellers sunde individer lever ofte med begge parasitter uden nogen
symptomer (Simonsen, 2004). I 2003 blev der i 23 harer undersøgt af Danmarks Veterinær Institut
kun fundet brucellose hos 2 individer (Danmark Veterinæinstitut, Årsberetning 2003,
www.dfvf.dk). Foruden ovennævnte angribes haren af en række forskellige parasitter som lus,
lopper, bændelorme. og rundorme
Harejagt i Danmark
I al den tid haren har været at finde i Danmark har mennesker drevet jagt på den. Haren er stadig en
af de vigtigste jagtbare arter i Danmark. Indtil for knap 10 år siden var haren således hvert år øverst
på listen over antal nedlagte pattedyr i Danmark (www.vildtudbytte.dk/dmu3.asp). Såvel harejagt
som harefangst har gennem tiden været en yndet beskæftigelse i Danmark. Af samme årsag er der
sket udsætninger af harer på flere danske øer. Blandt disse har en række øer i det sydfynske øhav
11
været kendt for harefangster. De indfangede dyr blev udsat på andre lokaliteter i Danmark eller
eksporteret til andre europæiske lande (http://www.sydforfyn.dk/harefang.htm).
I 1982 blev det, med en ændring i jagtloven, forbudt at bruge net under jagt. Dog med mulighed for
dispensation, hvis de indfangede dyr blev udsat på lokaliteter inden for Danmarks grænser. Et
endeligt stop for de årlige harefangster blev gennemført med en stramning af jagtloven i 1994 hvor
al udsætning blev forbudt. Denne ændring blev det definitive forbud mod harefangst. De seneste år
er der enkelte gange givet dispensation fra dette forbud. Senest fik en lokal jagtforening på Lyø i
november 2005 dispensation til indfangning af 12 harer til efterfølgende udsætning på naboøen
Halmø. Foruden indfangning af harer fra naturlige og udsatte populationer, blev der i 80 érne og
starten af 90 érne opført harefarme i Danmark. I 1993 da opdræt af harer blev forbudt ved lov, var
der ca. 100 harefarme tilbage i Danmark, som tilsammen eksporterede 5000 harer årligt (Kleist,
1995).
På baggrund af data fra vildtudbyttestatistikken, kan man få en ide om de jagtbare arters
bestandsudviklinger. Her vil generelle tendenser afspejles. Disse tendenser må ikke forveksles med
egentlige angivelser af absolutte bestandsstørrelser (Forchhammer & Asferg, 2000).
Med udgangspunkt i vildtudbyttestatistikkens oplysninger om jagtudbyttet af harer (figur 2) ses et
markant fald i udbyttet siden starten af 1960 érne. Et fald fra mere end 400.000 nedlagte dyr årligt i
perioden 1941-1960, til under 100.000 dyr de seneste 6 år. Det hidtil laveste udbytte blev
rapporteret i 2004 med mindre end 70.000 nedlagte dyr. Udbyttet er således i dag mindre end en ¼
af udbyttet i midten af sidste århundrede. Den samme udvikling ses i flere andre Vesteuropæiske
lande (Smith et al., 2005; Mitchell-Jones et al., 1999). Som følge af de seneste årtiers tilbagegang,
blev jagttiden på haren i Danmark i 2005 ændret fra perioden 1/10 til 31/1 til perioden 1/10 til
15/12.
Faktorer der påvirker harebestanden
Sammenfaldende med nedgangen i jagtudbyttet er der overalt i Vesteuropa sket en intensivering i
landbruget. Intensiveringen er derfor ofte blevet udpeget som primær årsag til de faldende
bestandstætheder (Tapper & Barnes, 1986). Men også andre faktorer som stigende predation
(Reynolds & Tapper, 1995; Schmidt et al, 2004), klima (Schmidt et al., 2004; Smith et al., 2005)
og sygdom (Haerer et al., 2001) er undersøgt som potentielle årsager. Med undtagelse af ekstreme
12
situation som meget højt jagttryk og sygdoms epidemier formodes den adulte overlevelse at være
relativ konstant (Marboutin et al., 2003). Fokus er der ofte blevet lagt på fekunditet og killinge-
dødelighed.
Den stigende intensivering inden for landbruget, har på flere måder potentiale til at påvirker
bestandstætheder. Større mark-enheder, med monokulturer af afgrøder som vinterbyg, udgør om
sommeren måske ikke nogen reel nærings-værdi for diegivende hunner og killinger, der behøver
føde med høj vand og næringsindhold (Hansen, 1991). Bortskaffelse af levende hegn mindsker
harens muligheder for passende dække om dagen, og udsætter dermed haren for større predation-
risiko. Øget mekanisering, medføre en stigning i antallet af killinger dræbt i forbindelse med
maskinel bearbejdning af markerne (Smith et al., 2005, A).
Stigende bestande af ikke kun ræv men også en række rovfugle har sandsynligvis medført stigende
predation, hovedsagelig på killinger og ung-harer (personlig kommentar, kontakt-personer fra
udvalgte lokaliteter).
I modsætning til predation og intensiveringer i landbruget har klima-ændringer med mildere vintre
vidste sig at være gavnlige for harebestanden (Schmidt et al., 2004). Milde vintre betyder lavere
dødelighed og højere reproduktion, begge vigtige parametre på bestandsniveau (Schmidt et al.
2004). På den anden side kan øget temperatur medføre en stigning i sygdoms overførsel imellem
individer, og i sidste ende medføre et fald i bestanden (Smith et al., 2005, A).
Kendskab til ovennævnte parametre er vigtige, når man ser på forvaltningsstrategier for at vende
den observerede tilbagegang hos haren. På samme måde er viden om harens populations dynamik
essentiel, hvis de sidste årtiers tendens skal vendes.
POPULATIONSDYNAMIK
Et af hovedformålet med økologi består i at beskrive, forstå og forklare fordeling og forekomst af
organismer. For at muliggøre dette, er det som økolog ikke nok at beskæftige sig med antallet af
individer, men også de demografiske processer (fødsler, dødsfald og migration) samt miljømæssige
faktorers virkning på disse.
13
Økologer beskæftiger sig ofte med begrebet population(er). En population er en gruppe individer af
samme art, der på samme tid befinder sig på et givet areal. Antallet af individer i en population
ændres over tid på baggrund af følgende parametre; fødsler (B), dødsfald (D), immigration (I) og
emigration (E). Denne ændring over tid kan udregnes efter følgende ligning (Begon et al., 2006):
Nnu = Nfør + B – D + I – E,
Hvor N er antallet af individer. I lukkede populationer hvor der ikke sker udveksling af individer
med andre populationer, afhænger populationens vækst udelukkende af fødsels- og dødsrater. Hvis
enten proportionen af dødsfald stiger eller proportionen af fødsler falder med stigende tætheder, er
populationen tæthedsafhængig. Hvis døds- og fødselsrater derimod forbliver stabile med stigende
tætheder anses populationen for tætheduafhængig (Sinclair et al., 2006).
En tæthedsuafhængig population med ubegrænsede ressourcer vil udvise eksponentiel vækst
beskrevet ved følgende ligning (Begon et al., 2006):
dN/dt = rN,
Hvor r er væsktraten.
I virkeligheden er den slags populationsvækst usandsynlig, idet ressourcer altid er begrænsede,
derfor vil en realistisk vækst-kurve altid være s-formet. I starten af kurven er ressourcerne i
overflod, døds-raten minimal og reproduktionen kun begrænset af fysiske parametre som
eksempelvis drægtighedsperioden og kuldstørrelse. Populationen vokser indtil en øvre grænse er
nået. Denne grænse kaldes for habitatets bærekapacitet (K). Bærekapaciteten er konstant for
pågældende forhold i pågældende habitat. Som populationen nærmer sig bærekapaciteten falder
vækstraten til 0, og populationen stabiliseres og opnår efterhånden en ligevægt. Naturlige
populationer vil ikke forblive i ligevægt i længere tid af gangen, men fluktuerer omkring dette
point.
14
Opstilling af life table
For at kunne forudse en populations fluktueringer i form af stigninger eller fald i antal, er det vigtig
at danne overblik over demografiske faktorers indvirkning på populationen. Dette gøres
eksempelvis ud fra informationer fra en life table.
Der findes to måder at opstille en life table på. Den direkte estimering af life table parametrene
kaldes kohorte life table, her følges alle individer i en population fra fødsel til død (Sinclair et al.,
2006). Denne form for monitering er som oftest meget tidskrævende og omkostningsfuld, især når
der er tale om en population med lang generationstid. Den indirekte estimering og mere
anvendelige, men desværre også mindre præcis life table, er den statiske life table. Data til en
statisk life table kan indhentes på flere måder. Ofte indfanges, mærkes og genudsættes individer fra
en population. Efter en bestemt tidsperiode genfanges individerne og overlevelsessandsynligheden
udregnes. En anden metode til opstilling af en statisk life table, består i at aldersbestemme døde
eller dræbte dyr. Denne metode giver et øjebliksbillede af aldersfordelingen i en population, og
dermed sandsynligheden for et individ at overleve fra en aldersklasse til den næste. En statisk life
table forudsætter følgende antagelser (i) den alderspecifikke fekunditet og overlevelse har været
kontant over flere generationer, (ii) indsamlede individer er repræsentative for aldersfordeling i hele
populationen, (iii) tilvækstraten r (rate of increase) skal være meget tæt på 0 (Sinclair et al., 2006).
En statisk life table baseret på aldersbestemte, døde dyr er anvendt i foreliggende undersøgelse.
Både kohorte og statisk life table består ofte af 6 kolonner
X, Inddeling af aldersklasse.
ax Antal af individer der har overlevet til begyndelsen af hver aldersklasse.
lx Overlevelserate. Proportionen af den oprindelige kohorte der har overlevet til begyndelsen af hver
aldersklasse. I den første aldersklasse vil lx altid være 1, da ingen af individerne er døde endnu.
dx Mortalitetsrate. Proportionen af den oprindelige kohorte der dør i hver aldersklasse, dvs.
sandsynligheden for at dø i intervallet x, x+1. Udregnet som forskellen mellem to efterfølgende lx
værdier.
qx Den alderspecifikke mortalitetsrate. Andelen af individer i hver aldersklasse, der ikke overlever
til aldersklasse. Udregnet som dx /lx.
px Den alderspecifikke overlevelsesrate. Andelen af individer i hver aldersklasse der overlever til
næste aldersklasse. Udregnet som 1-qx for hver aldersklasse.
15
Kolonnerne lx, dx, qx og px beskriver samme, data på hver sin måde. Afhængig af anvendelse
udvælges passende kolonne til beskrivelse af populationen. Bemærk at forskellige
kolonnebetegnelser kan forekomme.
Opstilling af fekunditets table
Mortalitet og fødselsrater er vigtige komponenter i populationsdynamikken. Fødselsrater kan
udregnes på flere forskellige måder, den meste anvendte er fekunditets-raten. For at opstille en
fekunditetstabel er det en forudsætning at man har kendskab til antal unger produceret fra hver
aldersklasse af hunner, samt kønsfordelingen af ungerne. For haren er det ved tælling af plancetale
ar, muligt at estimere antal af fødte unger i foregående ynglesæson Bray et al (2003) I forestående
undersøgelse er det antaget at køns-rationen af nyfødte hos harer er 50:50 (Hansen, 1991). I
fekunditet tabellen opstilles følgende kolonner;
x, Inddeling af aldersklasse.
ax Antal af undersøgte individer (kun hunkøn) i hver aldersklasse.
Bx Antal afkom fra hver aldersklasse.
mx Det gennemsnitlige antal afkom af hunkøn per hun, udregnet som bx/(2ax ) (Sinclair et al., 2006).
Anvendelse af life- og fekunditets table
Til sammen gør life table og fekunditetstabellen det muligt at udregne en populations
nettoreproduktionsrate R0, generationstid Tc og ekspotentielle vækstrate r (Begon et al., 2006).
Nettoreproduktionsraten R0 er udtryk for det gennemsnitlige antal unger produceret at et individ.
For arter med overlappende generationer udregnes;
R0 = Σ lxmx
Populationer med R0 > 1 vil stige i antal, mens populationer med R0 < 1 vil falde i antal af individer
(Begon et al., 2006).
16
Generationstiden Tc som er udtryk for det gennemsnitlige tidsinterval der går fra et individ fødes til
fødslen af dette individs afkom. Tc udregnes efter følgende formel;
Tc = Σ xlxmx/ lxmx Eller Tc = Σ xlxmx/ R0
Tc er kun en tilnærmelse for den sande generationstid T, da den ikke tager hensyn til at afkom kan
nå at reproducere sig, mens forældrene stadig er reproduktive. For arter med overlappende
generationer er Tc og Ro af begrænset anvendelighed (Caughley, 1967)
Ud fra Tc og R0 kan udregnes r, den ekspotentielle vækstrate således;
r = ln R0/ Tc
r er den vækstrate en population har potentiale til at nå. Men dette sker kun når overlevelses- og
fekunditetsrater forbliver konstante over længere perioder. Såfremt dette sker, vil vækstraten nærme
sig r, og samtidig vil populationen nærme sig en stabil aldersstruktur. Det vil sige at proportionen af
individer i hver aldersklasse forbliver konstant. I naturlige populationer svinger overlevelses- og
fekunditetsrater dog oftest over tid, hvilket medfører konstant ændring i vækstraten. Alligevel kan
den udregnede r-værdi være et nyttigt værktøj, hvis man eksempelvis ønsker at sammenligne
populationer af samme art fra forskellige miljøer og derved se hvilke miljø der fremstår som bedst
egnet for den pågældende art (Begon et al., 2006).
BESKRIVELSE AF STUDIEOMRÅDER OG INDSAMLET MATERIALE
Danmarks Miljøundersøgelser igangsatte i 2002 projekt markvildt, der har til formål at fastlægge de
primære årsager til de sidste årtiers nedgang i antallet af bl.a. harer i Danmark. I 2003 blev der
fordelt på 24 lokaliteter nedlagt og indsendt 390 harer til DMU (tabel 3). Lokaliteterne ligger spredt
ud over hele landet (figur 3), dog med overrepræsentation fra det sydøstlige Danmark. Her er
bestandstæthederne generelt højere end i resten af Danmark og det er dermed nemmere at indhente
et større antal dyr.
17
Harer blev primært nedlagt ved jagt, men suppleret med trafikdræbte dyr, sendt til DMU og
nedfrosset. I 2004 blev harerne optøet og obduceret af dyrlæger fra Danmarks fødevareforskning
(DFVF). Under obduktionen blev følgende udtaget fra hvert individ: kranium, et forben, et bagben,
et øje, en nyre, blodprøve, muskelprøve, mave samt ovarium fra hunnerne. Harernes vægt, længde,
kondition (vurderet på en skala fra 0-3 ud fra fedtlagring) samt eventuelle tegn på sygdom blev
noteret. Kranier, forben og bagben blev renset af Zoologisk Museum, København. Placentale ar i
livmoderen, er optalt af Trine-Lee Wincentz Jensen (DMU). For lokaliteter med 10 eller flere harer
indsendt til DMU (tabel 3), blev der indhentet yderligere information vedrørende arealudnyttelse,
predation, jagttryk og trafiktryk. Dette blev gjort igennem telefoninterview med kontaktpersoner fra
hver lokalitet (bilag 1). På baggrund af telefoninterview blev udregnet følgende parametre for hver
af de 11 lokaliteter; % af areal der opdyrkes med afgrøder og græsser (græsarealer med afgræsning
ikke medregnet), antal ræve nedlagt per ha per jagtindsats*(gennemsnit for perioden 2000-2005),
antal harer nedlagt per ha per jagtindsats* (gennemsnit for perioden 2000-2005), trafikintensitet
vurderet til 1,2 eller 3 (3 = høj trafikintensitet på vejnet i umiddelbar nærhed af jagtområder)(tabel
4).
*jagtindsats = (antal jagtdage x antal timer x antal jægere)/år
METODER TIL ALDERSBESTEMMELSE AF HARER
Visuel bedømmelse af vækstknuder Tilstedeværelse af tilvækstknuder (epifysebrusk) bruges hos harer primært til klassificering i to
grupper 1) juvenile og 2) voksne individer. Teknikken er baseret på at længdevæksten i de lange
rørknogler hos pattedyr foregår i såkaldte epifysebruske. Når længdevæksten afsluttes, forbenes
epifysebrusken og furen imellem epifysebrusk og ben forsvinder (Walhovd, 1966) (figur 4). Hos
haren finder dette sted i en alder af 7-9 måneder (Walhovd, 1966).
Alle indsamlede harer blev ud fra en visuel bedømmelse af tilstedeværelsen af epifysebruske på
forbenet, opdelt i juvenile og voksne individer. Følgende blev observeret under den visuelle
undersøgelse;
1) Epifysebruske øverst på overarmsben og nederst på spoleben (figur 5).
18
2) Nylig forbenet epifysebrusk på overarmsben og spoleben, synlig ved en lys linie i
epifyseregionen (figur 6).
3) Ingen epifysebrusk eller spor af sådan (figur 7). Alle individer med nylig forbenet
epifysebrusk blev sammen med individer uden epifysebrusk aldersbestemt nærmere ved
tælling af tilvækstlinier. For nærmere beskrivelse af metoden se manuskript I.
Øjenlinse vægt Da specialet blev påbegyndt var det intentionen at den juvenile del af materialet (bestemt ved
bedømmelse af epifysebruske) skulle yderligere aldersbestemmes ud fra øjenlinse vægt beskrevet i
tidligere studier (Andersen & Jensen, 1972; Cabon-Raczynska og Raczynski, 1972; Suchentrunk et
al., 1991; Kauhala & Soveri, 2001). Men efter at have undersøgt 27 dyr (7 juvenile og 21 voksne
harer) stod det klart at de udtagne øjne et sted i indsamlings- eller opbevaringsprocessen havde lidt
overlast. Af de 27 undersøgt harer var de 11 øjenlinser så beskadigede at det ikke var muligt at
udtag linserne i hel stand. Linserne der blev udtaget og tørret som beskrevet i Suchentrunk et al.
(1991) vejede i gennemsnit 33,8 mg for de juvenile og 194,8 mg for de voksne. Indsættes disse
værdier i tabel 1 fra Suchentrunk et al. (1991) ville det svare til en gennemsnitsalder hos de
undersøgte juvenile harer på 1,5- 6,1 dage og hos de voksne harer en gennemsnitsalder mellem
107,9-146,6 dage. Tilsvarende studier har fundet øjenlinse vægten af juvenile dyr til 102-185 mg og
voksne individer > 297 mg (Stott & Harris, 2006). Den gennemsnitlige kropsvægt at de undersøgt
dyr var hhv. 2791 g (juvenile) og 4253 g (voksne), så der var med sikkerhed ikke tale om helt små
killinger mindre end syv dage gamle. Herefter blev der indsamlet endnu 2 harer og øjenlinsen-
vægten bestemt straks efter indsamling. Hos disse to dyr blev øjenlinsevægt bestemt til 158 mg for
den juvenile hare og 258 mg for den voksen hare. Dette stemmer overens med tidligere studier
(Stott & Harris, 2006). Altså var det ikke metoden men materialets medtagede tilstand der
resulterede i uoverensstemmelserne mellem øjenlinse-vægten i dette og andre studiers. Denne del af
undersøgelsen blev herefter opgivet.
Tilvækstlinier i underkæben Metode benyttet i dette studie til tælling af tilvækstlinier er beskrevet i detaljer i manuskript I.
19
I midten af sidste århundrede blev tælling af tilvækstlinier i tænder (incremental growth lines)
anerkendt som en effektiv metode til aldersbestemmelse. Metoden blev de næste årtier afprøvet på
adskillige pattedyr efter (Grue & Jensen, 1979). På grund af den kontinuerer vækst i tænder hos
arter tilhørende langomorpha, kan denne metode ikke anvendes på eksempelvis europæisk hare
(Bernstein og Klevezal, 1965). Bernstein og Klevezal (1965) var de første til at forsøge sig med
tælling af tilvækstlinier i mandibelvæv i stedet for tandvæv. Siden da har en række studier evalueret
metoden (Ohtaishi et al., 1976; Frylestam & Schantz, 1977; Broekhuizen & Maarskamp, 1977;
Henderson & Bowen, 1979; Kovacs, 1983; Iason, 1988) og endnu flere har benyttet den (senest
Stott & Harris, 2006) på arter fra langomorpha. Langt størstedelen af litteraturen anser metoden for
brugbar, men samtidig er alle studier enige om at metoden ikke er uproblematisk.
Især tidspunktet for dannelsen af tilvækstlinier har medført diskussion om metodens brugbarhed
(Iason, 1988). Det har været foreslået at tilvækstlinierne dannes i løbet af efterårs- og
vintermånederne, hvor dyrenes vækst i forhold til resten af året sker med reduceret hastighed
(Ohtaishi et al., 1976). På dyr indsamlet i denne periode menes metoden derfor at være mindre
præcis (Iason, 1988). Dette udgør et alvorligt problem da mange studier udelukkende beskriver
aldersfordelingen på dyr indsamlet i netop disse måneder. Men da de faktorer der regulere
dannelsen af tilvækstlinierne ikke er kendt og dermed heller ikke det nøjagtige tidspunkt, er det
svært at kompensere for dette. Forskelle i klima, eksempelvis strenghed og længde af efterårs- og
vintermåneder i forhold til antal af tilvækstlinier har tillige været diskuteret (Broekhuizen &
Maarskamp, 1978; Iason, 1988).
Alle studier har som Bernstein & Klevezal (1967) fundet forskellige former for linier (se
beskrivelse i manuskript I). Enkelte studier var ikke i stand til at skelne mellem primære (annual
growth lines) og sekundære tilvækstliner (acessory lines) (Broekhuizen & Maarskamp, 1978). Dette
problem kan afstedkomme fejlbestemmelse, dog menes det at skyldes knaphed af materiale og
dermed manglende erfaring i at skelne mellem primære og sekundære linier (Broekhuizen &
Maarskamp, 1978).
For at opnå det best mulige resultat med metoden er det en fordel at være i besiddelse af
referencemateriale med kendt alder, hvormed det er muligt bliver kendt med formen og udseende af
de forskellige linier. Samtidig er det med et materiale med kendt alder muligt at verificerer
metoden. I dette studie blev et reference materiale venligst stillet til rådighed af Naturhistorisk
Museum i Aarhus. Reference materialet bestod af mandibler fra 32 harer indsamlet i perioden 1957-
1965 på den sydfynske ø Illumø. Harerne fra Illumø blev fanget som killinger, mærket og genudsat.
20
I efterfølgende år blev hare bestanden på Illumø fulgt tæt, død-fundne og harer nedlagt ved jagt blev
indsamlet og alderen på dødstidspunkt noteret.
I dette studie blev alle snit gennemset og vurderet to gange, med en måneds mellemrum. Snit der
blev vurderet forskelligt i de to gennemgange, blev vurderet endnu en gang. For at validere metoden
blev reference materialet gennemset og vurderet af to personer, uafhængigt af hinanden. For
beskrivelse af opnåede resultater med reference materiale se manuskript I.
REFERENCER
Abildgård, F. , Andersen, J. & Barndorff-Nielsen, O. 1972. The hare population (Lepus
europaeus Pallas) of Illumø island, Danmark. A report on the analysis of the data from 1957-1970.
Danish review of game biology 6 (5): 1-32.
Andersen, J. & Jensen, B. 1972. The weight of the eye lens in European hare of known age. Acta
Theriologica 17: 87-92.
Angelici, F. M. Riga, F. Boitani, L. Luiselli, L. 1999. Use of dens by radiotracked brown hares Lepus europaeus. Behavioural Processes 47: 205-208.
Begon, M., Harper, J.L. & Townsend, C.R. 2006. Ecology. 4th Edition. Blackwell science.
Oxford. UK: 378.
Bernstein, A. D. & Klevezal, G.A. 1965. Age determination of red pika (Ochotona rutila) and of
the longeared pika (Ochotona macrotis). Zoologicheskii zhurnal 44: 787-879.
Bray, Y., Marboutin, E., Peroux, R. & Ferron, J. 2003. Reliability of stained placental scar
counts in European hare. Wildlife Society Bulletin 31: 237-246.
Broekhuizen, S. & Maaskamp, F. 1979. Age determination in the European hare (Lepus
europaeus Pallas) in the Netherlands. Z. Säugetierkunde 44: 162-175.
21
Broekhuizen, S. 1982. Studies on the population ecology of hares in the Netherlands. Research
Institute for Nature management, Arnhem, Netherlands.
Caughley, G., 1967. Calculations og population mortality rate and life expectancy for thar and
kangaroos from the ratio of juveniles to adults. New Zealand Journal of science 10: 578-584.
Cabon-Raczynska, K. & Raczynski, J. 1972. Methods for determination of age in the European
hare. Acta Theriologica 7: 75-86.
Erlinger, S., Frylestam, B., Göransson, G., Höstedt, G., Liberg, O., Loman, J., Nilsson, I.N.,
Schantz, T. & Sylvén, M. 1984. Predation on brown hare and ring-necked pheasant populations in
southern Sweden. Holarctic Ecology, 7: 300-304.
Forchhammer, M.C. & Asferg, T. 2000. Invading parasites cause a structural shift in red fox
dynamics. Proceedings of the Royal Society of London 267: 779-786.
Frylestam, B. & von Schantz, T. 1977. Age dermination of European hares based on periosteal
growth lines. Mammel Review 7: 151-154.
Frylestam, B. 1980. Reproduction in the European hare in southern Sweden. Holarctic Ecology 3:
74-80.
Goszczynski, J. & Wasilenwski, M. 1992. Predation of foxes on a hare population in central
Poland. Acta Theriologica 37: 329-338.
Grue, H. & Jensen, B. 1979. Review of formation of incremental lines in tooth cementum of
terrestrial mammels. Danish Review of Game Biology 11: 1-48.
Haerer, G., Nicolet, J., Barcciarini, L., Gottstein, B. & Giacometti, M. 2001. Causes of
mortality, zoonoses and reproductive performance in European brown hare in Switzerland.
Schweizer archive für tierheillkunde 143: 193-201.
22
Hansen, Sørensen & Daugård, 1989. Bestandstørrelse og afgrødevalg hos hare (Lepus
europaeus). Landbrugsministeriets Vildforvaltning. 12s. Rapport fra Vildtbiologisk Station.
Hansen, K., Jessen Holm, M. & Simonsen, N.H. 1990. Harens (Lepus europaeus) fødevalg på
landbrugsarealer. Danmarks Miljøundersøgelser. 32s. Intern rapport afd. fra flora og faunaøkologi.
Hansen, K. 1991. Overlevelse og reproduktion i en dansk harebestand. Danmarks
Miljøundersøgelser. 36s. Faglig rapport fra DMU, nr. 30.
Hansen, K. 1992. Reproduction in European hare in a Danish farmland. Acta Theriologica 37: 27-
40.
Henderson, B.A. & Bowen, H.M. 1979. A short note: Estimating the age of european rabbit,
Oryctolagus cuniculus, by counting the adhesion lines in the periostreal zone of the lower mandible.
Journal of Applied Ecology 16: 393-396.
Iason, G.R. 1988. Age determination of mountain hares (Lepus timidus): A rapid method and when
to use it. Journal of Applied Ecology 25: 389-395
Jensen, B. 1993. Norden patterdyr. GEC Gads forlag: 1-325.
Kauhala, K. & Soveri, T. 2001. An evaluation of methods for disguising between juvenile and
adult mountain hares Lepus timidus. Wildlife Biology 7: 295-300.
Kleist, M. H. 1995. Haren 34. årgang nr. 1. NATUR OG MUSEUM. Naturhistorisk Museum: 1-
31.
Kovács, G. 1983. Survival patterns in adult European hares. Acta Zoologica Fennica 174: 69-70.
Marboutin, E. & Peroux, R. 1995. Survival pattern of European hare in a decreasing population.
Journal of Applied Ecology 32: 809-816.
23
Marboutin, E., Bray, Y., Peroux, R,. Mauvy, B. & Lartiges, A. 2003. Population dynamics in
European hare: breeding parameters and sustainable harvest rates. Journal of Applied Ecology 40:
580-591.
Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.,
Spitzenberger, F., Stubbe, M., Thissen, J.B.M., Vohralik, V. & Zima, J. 1999. The atlas of
European mammals. ACADEMIC PRESS. T & AD poyser Ltd: 1-484.
Morris, P. 1972. A review of mammalian age determination methods. Mammal Review 2: 69-104.
Muus, B. 1991. Danmarks Pattedyr 1. Gyldendalske boghandel, Nordisk forlag A.S: 1-174
Ohtaishi, N., Hachiya, N. & Shibata, Y. 1976. Age determination of the hare from annual layers
in the mandibular bone. Acta Theriologica 21: 168-171.
Pepin, D. 1989.Variation in survival of brown hare (Lepus europaeus) leverets from different
farmland areas in the Paris basin. Journal of Applied Ecology 26: 13-23
Reichlin, T., Klansek, E. & Hackländer, K. 2006. Diet selection by hares (Lepus europaeus) in
arable land and its implication for habitat management. European Journal of Wildlife Research 52:
109-118.
Reynolds, J.C. & Tapper, S.C. 1995. Predation by fox Vulpus vulpus o brown hares Lepus
europaeus in the central southern England, and its potential impact on annual population growth.
Wildlife Biology 1(3): 145-158.
Rödel, H.G. Völkl, W. Kilias, H. 2003. Winter browsing of brown hares: evidence for diet breadth expansion. Mammalian Biology, Zeitschrift für säugetierkunde, 69: 410-419.
Rühe, F. & Hohmann, U. 2004. Seasonal locomotion and home range characteristics of European
hares (Lepus europaeus) in an arable region in central Germany. European Journal of Wildlife
Research, 50: 101-111.
24
Schmidt, N. M., Asferg, T. & Forchhammer, M.C. 2004. Long-term patterns in European brown
hare population dynamics in Denmark: Effects of agriculture, predation and climate. BMC Ecology
4: 1-7.
Simonsen, N.H. 2004. Politikens jagtbog, 6. udgave, 3. oplag. Politikens forlag A/S. DK: 1-439.
Sinclair, A.R.E., Fryxell, J.M. & Caughley, G. 2006. Wildlife ecology, conservation and
management. 2th Edition. Blackwell publishing. Oxford. UK: 1-469.
Smith, R.K., Jennings, N.V. & Harris, S. 2005. A quantitative analysis of the abundance and
demography of European hares Lepus europaeus in relation to habitat type, intensity of agriculture
and climate. Mammel Review 35: 1-24.
Stott, P. & Harris, S. 2006. Demographica of European hare (Lepus europaeus) in the
Mediterranean climate zone of Australia. Mammalian Biology 71: 21.-226.
Suckentrunk, F., Willing, R. & Hartl, G.B. 1991. On eye lens weight and other age criteria of the
Brown hare (Lepus europaeus Pallas, 1778). Zoological Saügertierkunde 56: 365-374.
Tapper, S.C. & Barnes, R.F. 1986. Influence of farming practice on the ecology of the brown hare
(Lepus europaeus). Journal of Applied Ecology 23: 39-52.
Walhovd, H. 1966. Reliability of age criteria for Danish hares. Danish Review of Game Biology
4(3): 105-128.
25
TABELLER
Tabel 1: Europæisk brun hares taksonomi.
________________________________________________________________________________
Rige Række Underække Klasse Orden Familie Slægt Art
Dyr Chordata Vertebrata Pattedyr Lagomorpha Leporidae Lepus L. europaeus
26
Tabel 2: Tidligere studie af europæisk hare (Lepus europaeus)
Land Forfatter
Overlevelses-
rater
%
Juvenile
Killinger
per år*
Reproduktiv
aktive**
JUV AD
min max min max min max min max min max
Danmark
Abildsgård et al.
(1972) 0,59 21 65
Polen Pielowski (1976) 6,5 9,0
Sverige Frylestam (1979) 0,50
Polen Broekhuizen (1979) 0,34 0,38
Holland
Broekhuizen er al.
(1979) 0,35
Frankrig Pepin (1989) 0,25 0,50 5,1
Danmark Hansen (1991) 32 41 6,3 8,8 79 86
Danmark Hansen ( 1994) 21 65
Frankrig
Marboutin and
Peroux (1995) 0,51 42 67 10,0 12,5 85 90
Frankrig
Marboutin et al
(2003) 0,14 0,29 48 69 12,2 15,0 85 100
Europa Smith et al (2005) 0,27 0,33 32 52 7,3 8,2 82 88
*Gennemsnitlig antal killinger sat per hun per år
** % Hunner der var reproduktivt aktive
27
Tabel 3: Liste over lokaliteter, køn og aldersfordeling på indsamlede dyr, Antal i () bestemt
ved tælling at tilvækstlinier. Spørgeskema udsendt til kontaktpersoner fra lokaliteter
markeret med fed.
Lokalitet Females Males Ialt
Adulte Juvenile Adulte Juvenile
Anholt 2 (2) 2 (0) 3 (3) 3 (0) 10 (5)
Bornholm 5 (4) 7 (2) 5 (5) 4 (0) 21 (11)
Borreby 22 (20) 14 (0) 13 (13) 8 (1) 57 (34)
Borris 4 (3) 1 (0) 5 (5) 0 (0) 10 (8)
Brattingsborg 5 (4) 1 (0) 3 (3) 0 (0) 9 (7)
Enggård, Brønderslev 2 (1) 0 (0) 3 (3) 1 (0) 6 (4)
Feldborg Stskd. 2 (2) 0 (0) 0(0) 1 (1) 3 (3)
Frijsenborg 4 (4) 1 (0) 0 (0) 1 (0) 6 (4)
Giesegård 8 (6) 2 (1) 8 (6) 2 (0) 20 (13)
Gl. Kirstineberg 3 (3) 4 (0) 3 (2) 1 (1) 11 (6)
Hjelm 4 (4) 4 (0) 4 (4) 2 (0) 14 (8)
Kalø 1 (1) 0 (0) 1 (1) 0 (0) 2 (0)
Klosterhede 2 (2) 0 (0) 3 (3) 0 (0) 5 (0)
Margrethe Kog 1 (1) 5 (0) 4 (3) 10 (2) 20(6)
Mommer, Tommerby Fjord 0 (0) 0 (0) 0 (0) 1(0) 1 (0)
Orebygård 11 (9) 16 (1) 6 (5) 9 (3) 42 (18)
Overgård 4 (3) 0 (1) 1(1) 1(0) 6 (5)
Pandebjerg 26 (24) 7 (0) 12 (12) 9 (0) 54 (36)
Salling planteskole 1 (1) 3 (0) 2 (3) 4 (1) 10 (5)
Ukendt (label bortkommet) 0 (0) 1 (0) 1 (0) 1 (0) 3 (0)
Vennerslund 30 (29) 11 (3) 22 (21) 11 (5) 74 (58)
Vildsbøl plantage, Thy 2 (2) 0 (0) 3 (3) 1 (0) 6 (5)
Total 138 (125 ) 79 (8 ) 103 (96 ) 70 (14 ) 390 (236 )
28
Tabel 4: Samle skema med indhentede oplysninger om de 11 lokaliteterne
Lokalitets navn Areal Opdyrket land Jagtindsats Hare-densitet Ræve-densitet Trafiktryk
Vennerslund 570 82,6 120 5,1 0,83 Højt
Borreby 600 75,0 150 4,6 0,13 Lavt
Pandebjerg 695 64,7 120 3,8 0,69 Lavt
Orebygård 830 58,4 225 5,2 0,40 Lavt
Bornholm 370 39,2 550 2,3 0,00 Lavt
Giesegård 3100 48,4 125 0,6 0,67 Medium
Margrethe Kog 302 0,0 292 5,7 0,30 Lavt
Hjelm 63 11,1 100 18,3 0,00 Lavt
Gl. Kirstineberg 193 96,0 73 10,5 4,06 Lavt
Salling Planteskole 500 20,0 200 4,4 0,40 Lavt
Borris 4700 0,3 712 0,0 0,02 Medium
Opdyrket land % Opdyrket jord (inklusiv græsarealer uden afgræsning) ha
Jagtindsats Antal jagtdage x antal timer per dag x antal jægere/år (dagextimerxjægerer)/år
Hare-densitet (Antal dyr nedlagt per år/jagtindsats/areal)*10000 ((stk/(dagextimerxjægerer))/år/areal)*10000
Ræve-densitet (Antal dyr nedlagt per år/jagtindsats/areal)*10000 ((stk/(dagextimerxjægerer))/år/areal)*10000
Trafiktryk Estimeret af kontaktperson lavt/medium/højt
29
FIGUR FORKLARINGER
Figur 1: Kort over europæisk hares udbredelse i Europa (Mitchell-Jones et al., 1999)
Figur 2: Årlig jagtudbytte af europæisk hare i Danmark i perioden 1941 til 2004
(http://vildtudbytte.dmu.dk/)
Figur 3: Kort over de lokaliteter hvor de indsamlede harer er nedlagt, lokaliteter der har bidraget
med mere end 9 harer er markeret med fed.
Figur 4: Forskellige grader af forbening af epifysebruske øverst på overarmsbenet (fra venstre mod
højre, helt åben epifysebruske til helt forbenet epifysebruske, uden synlig fure).
Figur 5: Juvenile individer, med tydelig epifysebruske ved både overarmsben og spoleben
Figur 6: Individer, med nylig forbenet epifysebruske synlig ved overarmsben
Figur 7: Voksne individer, uden epifysebruske eller spor efter sådanne
Bilag 1: Spørgeskema udsendt til kontaktpersoner fra hver lokalitet og gennemgået over telefonen.
30
FIGURER
Figur 1
31
Figur 2
År
32
Figur 3
Vennerslund
Pandebjerg
Gl. Kirstineberg Orebygård
Borreby
Bornholm
Hjelm Giesegård
Salling planteskole
Borris
Margrethe kog
Anholt
Kalø
Brattingsborg
Brønderslev
Feldborg
Frijsenborg
Vilsbøl
33
Figur 4
34
Figur 5
35
Figur 6
36
Figur 7
37
BILAG 1
Spørgeskema vedrørende arealer hvor indsendte harer er nedlagt
Revir
1) Om muligt vedlæg kort hvor jagtarealer er indtegnet.
2) Areal fordeling på jagttidspunktet (oktober –november 2003)
Biotoptype Areal (Ha) Evt. kommentar
Skov/Plantage
Græsarealer uden
afgræsning
Græsarealer med
afgræsning
Agerbrug
Brak
Eng
Sø/vandløb/mose
Småbiotoper
Andet sandørken
Biotoppleje
3) Er der foretaget biotoppleje med henblik på harer på lokaliteten
Plejetype Sæt X Evt. Kommentar
Vildtager
38
Anlæg af bredere læhegn
Spøjtefrie randzoner
Andet
Harer:
4) Estimat af tætheden af harer på reviret 1 oktober 2003:
Tætheder Individer per km2 Sæt X Evt. kommentar
Meget høj >20
Høj 11-20
Middel 6-10
Lav 2-5
Meget lav <2
5) Udviklingen i harebestanden på reviret:
Bestanden er: Sæt X Evt. kommentar
Faldende
Stabil
Stigende
39
Predation på harer:
6) Sæt X ved de arter som jævnligt observeres på arealerne (min. 1 gang per halve år):
Art Observeret (sæt X) Yngler i området
(sæt X)
Evt. kommentar
Duehøg
Musvåge
Ugle
Ravn
Krage
Husskade
Ræv
Mår
Kat
Andre (hvilke)
7) Antal kuld rævehvalpe i reviret (2003) __________stk.
8) Udviklingen i rævebestanden på reviret:
Bestanden er: Sæt X Evt. kommentar
Faldende
Stabil
Stigende
40
Trafikintensitet:
9) Vejnet i umiddelbar nærhed af revir består af:
Vejtype: Længde (km) Evt. kommentar
Motorvej
Motortrafikvej
2-sporet landevej
Mindre landevej
Grusvej
Markvej
10) Hvor ofte observeres der trafikdræbte harer på ovenstående veje:
Hyppighed Sæt X Evt. kommentar
1-2 gange per måned
1-2 gange per halve år
1-2 gange per år
Aldrig
Jagtintensitet:
11) Nedenstående skema udfyldes så detaljeret som muligt, i forhold til tilgængelig information.
Med hensyn til jagtdatoer, jagtintensitet og udbytte på reviret, i perioden efteråret 2000 til forår
2005 (ved manglende oplysninger for hver enkelt jagt noteres evt. gennemsnits tal for hver kolonne
for hvert år):
Antal
jagter
per år
Antal
jægere
Antal
jagttimer
Antal nedlagte
harer
Antal nedlagte
ræve
Evt. kommentarer (eks.
Jagtform)
41
12) Sker der regulering i afskydningen af harer på reviret:
Hvis ja,
hvordan:_________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
__________________
13) Andre generelle kommentarer omkring harebestanden på reviret (eksempelvis
trivsel/sygdomme):
42
MANUSKRIPT I
ESTIMATION OF AGE IN EUROPEAN BROWN HARES (Lepus europaeus),
BASED ON PERIOSTEAL GROWTH LINES.
Rikke Mørck Nielsen1, 2
1Department of Population Ecology, Institute of Biology, University of Copenhagen,
Universitetsparken 15, DK-2100 København Ø, Denmark.
2Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute,
Kalø, Grenåvej 12, DK-8410 Rønde, Denmark.
E-mail: [email protected]
Word count: Total: 2631
Text: 2093
Number of references: 16
Number of tables/figures: 1/6
43
Short communication
ESTIMATION OF AGE IN EUROPEAN BROWN HARES ( Lepus europaeus), BASED ON
PERIOSTEAL GROWTH LINES.
By RIKKE MØRCK NIELSEN
Institute of Biology University of Copenhagen, Copenhagen
Key words: Lepus europaeus, age determination, periosteal growth lines, lower mandible
Introduction:
When dealing with population ecology the ability to obtain a correct age distribution for the species
in question is often crucial. For decades researchers have argued which methods are best for the
purpose, when looking at long lived animals, such as many species of mammals (Morris, 1972). A
frequently used and well documented method is age determination based on annual growth lines in
teeth. Due to the continuous growth of the teeth in Langomorphs, annual formed lines in these can
not be used (Klewezal & Kleinenberg, 1967). In stead growth lines in bone tissue of the lower
mandible, have been use to determine age in several Langomorph species. Only a few studies have
included known age material (Ohataishi et al., 1976; Henderson & Bowen, 1979; Iason, 1988) and
even fewer have been published for the species Lepus europaeus (Frylestam & Schantz, 1977;
Broekhuizen & Maaskamp, 1979). In addition the number of animals of known age in these studies
are very limited (20 & 4). Growth lines are assumed to form during winter, caused by slower
metabolic rate causing slower growth of bone tissue. This results in thinner and more compact
growth layers than formed during summer (Klewezal & Kleinenberg, 1967). The process of growth
line formation is to this day, not fully understood. The aim of the present study was to evaluate the
accuracy of using periosteal growth lines to determine age in European brown hare (Lepus
europaeus). Additionally a detailed age structure of a recent Danish sample of culled hares is
presented, as an example of an application of this method in population biology.
44
Materials and methods:
The material consists of two parts: 1) 32 hares of known age (juvenile < X < 7 years) from a natural
population on the Island of Illumø, situated to the south of Funen (Denmark). The hares were
captured as leverets, marked and culled or collected at death during the years 1957-1965. Shortly
after collection the bones were treated with 3% hydrogen peroxide (H2O2) and afterwards stored in
cardboard boxes at the Museum of Natural History in Aarhus (Abildgård et al. 1972). In 2005 one
lower mandible from each of the 32 animals was retrieved and prepared as described below. 2) 390
hares of unknown age colleted in Denmark during 2003, mainly culled during the months of
October, November and December. The hares were separated into adult and juveniles determined
by presence of epiphyseal cartilage in juveniles (Walhovd 1966). At the Royal Dental College in
Aarhus, one lower mandible from all 242 adult and 16 juvenile animals was prepared as following.
A section between the first and second premolar was cut and the sections were decalcified for 24
hours in 10% formic acid (HCOOH), dehydrated over a period of 6 days, infiltrated and embedded
in methylmetacrylat (MMA). Transverse sections (approximately 7 mym) were cut on a freeze
microtome. The transverse sections were overstained for 10 min, with 0.1% toluidinblue. Different
dyes were tested among others the Weigerts haematoxylin used by Frylestam & Schantz (1977), but
the toluidinblue resulted in the most visible and distinct lines. Once dyed, the sections were viewed
in a microscope and the number of visible lines was counted. Two interpreters (interpreter A and B)
investigated the mandible sections of the hares of known age independently. The hares colleted in
2003 were only investigated by interpreter A.
Results:
Lines were found in all sections. The position of the best place to count varied within each section,
though most often lines were most easily counted on the central and upper lateral side of the
mandible (figure 1). As described in earlier studies (Klewezal & Kleinenberg, 1967; Ohtaishi et al.
1976; Frylestam & Schantz, 1977) three types of lines were observed. The resorption line (RL) was
visible in all hares from Illumø, as a weak and wavy line between the mesosteal and the periosteal
bone. However RL was absent in some of the young animals colleted in 2003. In hares more than 1
year of age, the RL often became less distinct. The adhesion lines (annual growth lines, AGL) were
visible in all hares 1 year of age or older. Often the AGL were only clear and distinct in one or at
few sections of each slide. The AGL in hares of more than 1 year of age were not always identical
45
in thickness and visibility (figure 1). The third type of line observed was the accessory lines (AL)
first described by Klewezal & Kleinenberg (1967). These lines are less distinct, often not as thick as
AGL and in most cases at some point they converge with an AGL (figure 1). The AL are thought to
emerge as a result of short-term disruptions in the animal’s life (Morris, 1972).
Figure 1: Right: section of lower mandible. Left: magnification of lower mandible from hare 2 years of age. Two
annual growth lines (AGL), one accessory line (AL) and the resoption line (RL)
are visible.
As illustrated in figure 2 there are no perfect agreement between the known age and the estimated
age. The interpreters had estimated the correct age for 15 and 16 animals each. Interpreter A could
not estimate age in one individuals and interpreter B could not estimate age in four individual (table
1). This is equivalent to 48.4 % and 57.1 % correct age estimates respectively. Within + 1 year of
known age the interpreters estimated the true age in 83.9% and 78.6 % of the hares respectively. No
systematic error for the different age-classes is obvious, when looking at proportion of animals
estimated to the correct age (figure 3). Therefore no adjustments for over- or underestimating have
been applied to the age determined for hares of unknown age. All hares aged 5 or more were
estimated to the exact age or younger (figure 2). This could be due the interpreters´ awareness that
few hares reach high ages.
AL
RL
1. AGL
2. AGL
46
01
23
45
67
8
0 1 2 3 4 5 6 7 8
True age
Est
imat
ed a
ge
1. interpreter 2. interpreter Expected
Figure 2: Estimated age plotted against true age
For the animals of known age, there were no significant difference in number of males (n=19) and
females (n=12) (χ2= 1.58, P=0.21, df =2) (χ2-test). Also there were no significant difference in
number of male (n= 8/8) and females (n= 7/8) that interpreters estimated to the correct age
(χ2=0.07, P=0.21, df =2 and χ2=0.00, P=1, df =2)( χ2-test).
With a Wilcoxon test for matched pairs, there is no significant difference between the true age and
the estimated age for either interpreter (T = 45.5, P < 0.05, df =30 and T = 35.5, P < 0.05, df =27).
Furthermore the estimated age did not differ significantly between interpreters (T = 77.5, P < 0.05,
df = 27). Confidence limits for both interpretations are shown in appendix figure 1 and 2.
Table 1: True and estimated age by the two interpreters.
Estimated age (first/second interpreter)
True age n Juv. 1 2 3 4 5 6 No Est. Juv. 1 1/1 1 5 0/3 4/0 0/1 1/0 0/1 2 5 1/0 4/2 0/1 0/2 3 5 1/0 3/3 1/2 4 5 0/1 2/0 3/1 0/2 0/1 5 5 2/1 3/4 6 5 1/1 1/0 1/1 1/2 1/1 7 1 0/1 1/0
47
0
0,2
0,4
0,6
0,8
1
1,2
0 1 2 3 4 5 6 7
True age
Pro
porti
on (
%)
Correct age +/- 1 year +/- 2 years
Figure 3: Proportion of aged animals estimated to the true age
Of the 390 hares colleted in 2003 age was determined for 372. The age of 18 animals was not
determined due to missing mandible or poor quality of sections. Less than 4% of the hares was
estimated to be >4 years of age (figure 4). The oldest animal was a female determined to be 8 years
of age. No males were found to be more then 5 years of age (figure 4).
0
10
20
30
40
50
0-1. 1-2. 2-3. 3-4. 4-5. 5-6. 6-7. >7
Estimated age
Fre
quen
cy (
%)
Females N=206 Males N=166
Figure 4: The age structure of 376 hares colleted in Denmark in 2003. X-axis represents percentage of individuals in
each sex.
48
Discussion:
The hares from Illumø showed weaker growth lines than the sampled hares from 2003. This is
likely to be a result of the treatment 4 decades ago with hydrogen peroxide (H2O2) (Frylestam &
Schantz, 1977) as well as ageing in general. It could also be due to differences in winter climate in
the years preceding the collection of the material. The known age material in Frylestam & Schantz
(1977) and this study originate from the same material from Illumø. Compared to Frylestam &
Schantz (1977) who found an 85% agreement between the true age and the estimated age, this study
generated a slightly smaller agreement. This could indicate a degeneration of the quality over time,
and/or is an effect of the interpreters experience in ageing.
In previous studies the known age material ranged from juvenile to 4 years of age (Frylestam &
Schantz, 1977). In the present study the material ranges from juvenile to hares 7 years of age. In
animals of more the 3 years of age, the interpreters underestimated the age for 53.3 % and 33.3 %
for the aged animals respectably. This could indicate that age is more likely to be underestimated in
old animals compared to young animals. Broekhuizen & Maaskamp (1979) were unable to reliably
distinguish between the AGL and AL. They explained this as an effect of the mild Atlantic winters
in the Netherlands, several years prior to their study. Another explanation could be their low
number of hares of known age and as a consequence, lack of experience. In the present study
interpreter A had no prior experience in looking at growth lines, while interpreter B had done
previous work with age determination in red fox (Vulpes vulpes).
The fact that age class 1-2 years showed a lower female frequency than expected is difficult to
explain. This age class was be expected to follow the trends of the neighbouring age classes. It can
not be explained by low recruitment in one year since the male frequency for the age class 1-2 years
is as expected. In the remaining age classes females showed a slightly higher frequency than males,
which is in accordance with previous studies from Denmark, where females (0.45) showed a
slightly higher survival rate then males (0.38) (Abildsgård et al. 1972). The opposite was found in a
resent study from France (Marboutin et al. 2003) where adult male survival (0.55) was higher than
adult female (0.50) survival. Marboutin et al, (2003) gave no further explanation to why the male
survival rates were higher than females, they only conclude that males usually survive better than
females.
49
It has been suggested that reproductive cycles could influence the formation of growth lines in
mammals (Grue & Jensen, 1979), but so far no investigations have been made on the variation in
number of periosteal lines in relation to sex in European hare. In the present study no evidence of
variation in number of lines or reliability of the method between sexes was found.
The found juvenile frequency (39.5%) is lower than Smith et al. 2005 found (48-52%). The results
in the present study could be biased due to the fact that most hares colleted were culled by hunters,
who might show a preference to avoid shooting leverets (personal comment from interviewed
hunters). Also juvenile mortality is expected to be higher than adult mortality (Hansen, 1994),
leaving the number of juveniles in autumn lower than expected, compared to studies based on the
number of juveniles born per adult animal (Mørck in prep).
The hares in the present study were collected from more than 20 different locations in Denmark.
Between locations there were large differences in land use, predation- and traffic-intensity as well
as hare-densities, all resulting in significant differences in age distribution among location (Mørck
in prep). Looking at all the collected hares as one population, would erase otherwise obvious
tendencies from each location, such as very high proportions of juveniles or the reverse. The
observed age distribution for hares collected in the present study may therefore only be regarded as
a rough estimate, without much explanatory value.
Other parameters for age determination of the European hare are body weight, eye lens weight,
length of hind foot and ear, ossification of the epiphyseal cartilage of the ulna and the radius
(Kauhala & Soveri, 2001; Suchentrunk et al. 1991; Andersen & Jensen, 1972; Broekhuizen &
Maaskamp, 1979). These methods only allow for separation into adult or juvenile age categories.
Therefore for the moment the only and best method for age determination for hares of more than 1
year of age, is counting growth lines in mandible sections. It is however crucial to be aware of the
uncertainties involved when using this method. A better understanding of why and when the growth
lines are generated would highly improve the technique.
Acknowledgment
Danmarks Miljøundersøgelser (NERI) for funding the project. The materials used in this study were
collected by Birger Jensen and kindly made available by the Museum of Natural History in Aarhus.
Gösta Nachman, Tommy Asferg and Trine-Lee Wincenzt Jensen, for criticism of previous drafts.
50
Preparation and sectioning of mandibles were done by Jette Barlach and Sussi Madsen, from the
Royal Dental College, Unviersity of Aarhus, to whom I am very grateful for their work.
References
Abildsgård, F., Andersen, J. & Barndorff- Nielsen, O. 1972. The hare population (Lepus
europaeus Pallas) of Illumø island, Denmark. A report on the analysis of the data from 1957-1970.
Danish Review of Game Biology 6(5): 1-32.
Andersen, J. & Jensen, B. 1972. The weight of the eye lens in European hare of known age. Acta
Theriologica 17: 87-92.
Broekhuizen, S. & Maaskamp, F. 1979. Age determination in the European hare (Lepus
europaeus Pallas) in The Netherlands. Z. Säugetierkunde 44: 162-175.
Frylestam, B. & Schantz, T. 1977. Age determination of European hares based on periosteal
growth lines. Mammel Review 7: 151-154.
Hansen, K. 1994. Unge harer i jagtudbyttet. Faglig Rapport fra DMU (30): 1-20.
Henderson, B.A. & Bowen, H.M. 1979. A short note: Estimating the age of European rabbit,
Oryctolagus cuniculus, by counting the adhesion lines in the periostreal zone of the lower mandible.
Journal of Applied Ecology 16: 393-396.
Iason, G.R. 1988. Age determination of mountain hares (Lepus timidus): A rapid method an when
to use it. Journal of Applied Ecology 25: 389-395.
Grue, H.& Jensen, B. 1979. Review of the formation of incremental lines in tooth cementum of
terrestrial mammals. Communication No 162 From Vildtbiologisk Station Kalø, Denmark:1-48.
Kauhala, K.& Soveri, T. 2001. An evaluation of methods for disguising between juvenile and
adult mountain hares Lepus timidus. Wildlife Biology 7: 295-300.
51
Klevezal, A.G. & Kleinenberg, S.E. 1967. Age determination of mammals by layered structure in
teeth and bones. Academic science of the USSR. Severtzov Institute of Animal Morphology.
Translated by Israel Program for Sciences Translations (1969): 1-128.
Marboutin, E., Bray, Y., Peroux, R., Mauvy, B. & Lartiges, A. 2003. Population dynamics in
European hare: breeding parameters and sustainable harvest rates. Journal of Applied Ecology 40:
580-591.
Morris, P. 1972. A review of mammalian age determination methods. Mammal Review 2: 69-
104.
Ohaishi, N., Hachiya, N. & Shibata, Y. 1976. Age determination of the hare from annual layers in
the mandibular bone. Acta Theriologica 21: 168-171.
Smith, R.K., Jennings, N.V. & Harris, S. 2005. A quantitative analysis of the abundance and
demography of European hares Lepus europaeus in relation to habitat type, intensity of agriculture
and climate. Mammal Review 35: 1-24.
Suckentrunk, F., Wiling, R. & Hartl, G.B. 1991. On eye lens weight and other age criteria of the
Brown hare (Lepus europaeus Pallas, 1778). Z. Saügertierkunde 56: 365-374.
Walhoved, H. (1966): Reliability of age criteria for Danish hares. Danish Review of Game Biology
4 (3): 105-128.
52
Appendix
Figure 1: 95 % confidence limits for interpreter A.
-2
0
2
4
6
8
10
0 2 4 6 8 10
True age
Est
imat
ed a
ge
Figure 2: 95 % confidence limits for interpreter B.
-2
0
2
4
6
8
10
0 2 4 6 8 10
True age
Est
imat
ed a
ge
53
MANUSKRIPT II
POPULATIONS DYNAMICS OF EUROPEAN HARE (Lepus europaeus) IN 11
DANSIH LOCATIONS.
Rikke Mørck Nielsen1, 2
1Department of Population Ecology, Institute of Biology, University of Copenhagen,
Universitetsparken 15, DK-2100 København Ø, Denmark.
2Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute,
Kalø, Grenåvej 12, DK-8410 Rønde, Denmark.
E-mail: [email protected]
Word count: Total: 7695
Abstract: 131
Text: 4140
Number of references: 36
Number of tables/figures: 21/2
54
POPULATIONS DYNAMICS OF EUROPEAN HARE ( Lepus europaeus) IN 11
DANSIH LOCATIONS.
By Rikke Mørck Nielsen Institute of Biology University of Copenhagen, Copenhagen
Abstract
Age, length, weight and reproductive success were determined in 320 European hares, collected at
11 different locations in Denmark. Life tables were constructed on the basis of the estimated
reproductive parameters and stage specific survival-rates were calculated. Significant difference in
weight, length and mean age were found between location. In adult 74.3% of the females were
found to be reproductively active, with a mean number of 7.4 leverets produced per adult female.
Juveniles made up 40.6% of the aged animals. No difference was found in mean age of female and
male hares. The mean survival-rate for juvenile hares was significantly higher than mean survival-
rate for leverets. No significant difference was found between adult and leveret mean survival-rate.
It was attempted to construct explanatory models for reproduction success and stage specific
survival-rates.
Keywords
European brown hare (Lepus europaeus), age determination and distribution, reproductive success,
explanatory models.
Introduction
Only a few decades ago, the European hare (Lepus europaeus) was the most abundant mammal
game species in Denmark, counting more then 350.000 animals culled a year. In 2000 the number
of hares culled was down to less then 84.000 (http://vildtudbytte.dmu.dk/dmu2.asp). Hunting
records from the rest of Europe show the same tendencies for the European hare (Broekhuizen,
1982; Michell-Jones et al, 1999; Smith et al, 2005, A). Even though the hunting bag record is not an
55
absolute measure of population size, it is regarded the best estimate available, when a direct
counting of animals is not an option (Tapper & Pearsons, 1984). As a result of the decline the E
uropean hare was included in the Danish Yellow list in 1997. The list consists of
plants and animals in Denmark not yet threatened by extinction, but requiring special attention
(Stoltze, 1997). Similar actions have been taken in other European countries (Bern Convension;
Michell-Jones et al. 1999).
The European hare thrives in cultural landscapes and are more abundant in arable farming areas
than in pasture, uplands and woodland (Tapper & Parsons, 1984; Klansek et al, 1998; Vaughan et
al, 2003). Preference for these habitats leave the European hare vulnerable to the massive changes
that have taken place in the agricultural sector within recent decades. Increased use of large
machinery has induced field-size to increase and the number of hedgerows to reduced. The
hedgerows provide the hares with cover during daytime. Increased use and efficiency of pesticides
have reduced the amount of herbs in crop-stands. In order to convert or as a minimum stop the
decline of the European hare it is crucial to know the underlying causes. The ultimate cause of the
decline is believed to be habitat change through intensification of agricultural practice (Vaughan et
al, 2003; Lundstöm-Gilliéron & Schlaepfer, 2003; Tapper & Barnes, 1986; Smith et al, 2005, A).
Despite several studies the proximate cause is still unclear. Low quality or scarcity of resources may
be the cause (Frylestam, 1980; Tapper & Barnes, 1986; Hansen et al, 1990; Reichlin et al, 2006).
Others have found predation to be the main factor (Reynolds & Tapper, 1995; Goszczýnski et al.,
1992; Schmidt et al, 2004). Parameters such as increased traffic, disease and climate have also been
suggested (Marboutin & Peroux, 1995; Hansen et al, 1989; Hackländer et al, 2002; Haerer et al,
2001).
The objectives of the present study are (i) to estimate ages of collected hares (ii) to examine
possible differences in weight, length, reproduction, age and survival-rates between local
populations (iii) to construct explanatory models for the observed differences between local
populations.
Material and methods
The National Environmental Research Institute (NERI) collected 333 carcasses of European hare
culled during the hunting season of 2003 (1/9- 31/12). The hares were culled by the local hunters at
11 different locations in Denmark (appendix 1, figure 1). The carcasses were stored at -18°C until
56
autopsied by veterinarians. Following samples were retrieved from each individual: skull, one front
leg, one hind leg as well as uterus from the females. The hares weight, length and fitness (rated on a
scale from 0-3 depending on fat layer) were recorded. The bones were cleaned free of flesh. Based
on a visual examination of epiphyses fusion on front leg (Morris 1972) the juvenile hares were
separated from the adult hares. Mandibles of 17 juvenile and 235 adult hares were prepared as
described by Mørck (in prep). For control purposes mandibles from 32 hares of known age were
included. No systematic error due to method was obvious for the known age material, therefore no
adjustments for over- or underestimating was applied to the age determined for the hares of
unknown age. The result of age-determination of hares of known age are presented in Mørck (in
prep).
Number of placental scars was counted following established procedures (Bray et al., 2003).
Data concerning proportion of area used for crop and pasture, predation-, hunting- and traffic-
intensity and estimates of hare and fox densities were gathered though telephone interviews with
contact-persons from each of the 11 locations.
Results
There was no significant difference in the proportion of females and males in the juveniles (χ2 =
0.63, P = 0.23, df = 1). However there was a significant difference between the proportion of adult
females and adult males (χ2 = 4.85, P = 0.023, df = 1) (appendix 1, table 1).
Using a Generalized Linear Model (GLM) the following differences were found for length and
weight. There was no significant difference in the mean length of adult females and males
(F = 0.40, P = 0.53, df = 185). The same is true for the juvenile females and males (F = 4.04, P =
0.05, df = 119).
The adult females were significantly heavier than the adult males (F = 8.32, P < 0.0001, df = 186).
However there were no significant difference between the weight of the juvenile females and males
(F = 6.32, P < 0.0001, df = 122).
Between locations following results were obtained from the GLM model. The mean length of adult
animals from Hjelm was significantly shorter than from the rest of the locations, except Borris and
Salling Planteskole. (F = 4.99, P < 0.0001, df = 196). The mean length of the juvenile animals from
Hjelm was also significantly shorter than the mean of the juvenile animals from the rest of the
locations, except Salling Planteskole (F = 6.50, P < 0.0001, df = 119). The juvenile hares from
57
Margrethe Kog, Hjelm and Salling Planteskole weighted significantly less then the juvenile hares
from Borris and Gl. Kirstineberg (F = 6.32, P < 0.0001 df = 119) (appendix 1, table 2-3). Also the
adult hares from Hjelm weighted significantly less than the adult hares from the rest of the locations
(F = 8.32, P < 0.0001, df = 186) (appendix 1, table 4-5).
There was a significant difference in the mean condition of the animals between locations (Kruskal
Wallis test: χ2 = 36.22, P < 0.0001). Using a Mann-Whitney U-test on condition (fat-deposition) for
each location no significant difference was found between female and male hares (13.5 < U <
433.5, 0.083 < P < 0.85).
Age-related productivity for the collected hares was as shown in table 3. From the 11 locations 59.8
% of the collected females (91.3 % of adult females) from the 11 locations were examined and scars
counted. Visible scars was found in 74.3 % of the examined adult females. The mean number of
scars in adult females was 7.4 resulting in 3.7 females produced per adult female (appendix 1, table
6). A significant difference in the number of scars per female was found between the 11 locations
(PROC GENMOD, Possion distribution: χ2 = 98.21, P < 0.0001) (appendix 1, table 7). An
explanatory model for number of scars was constructed (see below)
The age of 186 adult and 134 juvenile hares was determined (appendix 1, table 8). The age of 13
adults was not determined due to bad mandible cuts. Juveniles made up 40.6% of the aged animals.
No difference was found in mean age of female and male hares from each location (Mann-Whitney
U-test: 10.0<U<417.5, 0.11<P<1.00). However the mean age was significantly different between
the 11 locations (ANOVA: F=4.26, P<0.0001) (appendix 1, figure 2). The age distribution was
significantly different between locations (Kolmogorov-smirnov test) (appendix 1, table 9).
A life-table for each location was constructed. The expected number of leverets to be shoot at each
location, had hunting been executed during the reproduction period, was calculated. This was done
by dividing the number of shoot adult hares by 2 and multiplying with the average number of scars
counted (appendix 1, table 7) in adult females hares from each location. These values were used to
construct the life-tables for each location (appendix 1, table 10-21). In 6 locations “negative death”
occurs. This is of course a biologic impossibility, thus all the samples have been smoothed. Adult
mortality is assumed to be constant. Thus the proportion of survivors (lx) should decrease
exponentially with age. Regression between the variables age (x) and the natural logarithm to the
observed survivorship (ln(lx)) yields a linear relationship. The linear relationship was used to
58
construct the smoothed ln(lx). The age-classes 0 and 0,5 years were excluded as different mortality-
rates were expected as compared to adult hares. The mean survival-rates were as follows, leverets
(mean = 0.36, SD = 0.15), juveniles (mean = 0.55, SD = 0.25), adults (mean = 0.52, SD = 0.14).
The mean stage-specific survival-rate for juvenile hares was significantly higher than the mean
survival-rate for leverets (ANOVA: F = 4.22, P = 0.024). No significant difference in mean
survival-rate between adults and leverets was found. An explanatory model for stage specific
survival was constructed (see below).
The procedure PROC GENMOD in SAS was used to fit a multiple logistic regression model to
empirical data. This was done in order to identify possible factors influencing the number of
counted placenta scars. The collected data was presumed to follow a negative binomial distribution.
The following variables were used in the full model: age (years) of the female (X1), weight (g) of
the female (X2), percentage of area used for crop and pasture (X3) and hare density (number of
hares culled per hunter unit* per ha) (X4)(appendix 2). The weight (g) of the female, the percentage
of area used for crop and pasture and hare density were not included in the reduced model, due to
non-significant χ2 values (P< 0.05) (appendix 2).
The procedure Generalized linear Model (GLM) in SAS was used to fit a model to empirical data.
Juvenile animals were not included in the model. The following five predictor variables were used
to create a model for the calculated survival-rates a(x): Fox density at location (number of foxes
culled per ha per hunter unit* ) (X1), hare density at location (number of hares culled per ha per
hunter united*) (X2), percentage of area used for crop and pasture (X3), fat-deposition
(0,1,2,3)(X4,X5 X6 and X7), and traffic intensity at location (estimated to low/medium/high) (X8,X9
and X10). Full and reduced model presented in appendix 3. Fat-deposition and traffic intensity were
not included in the reduced model, due to non-significant F values (P < 0.05). The reduced mode
explains 13.6% of the observed differences in stage specific survival-rates between locations.
*hunter unit = (number of hunting days x number of hunters x number of hours spent hunting)/per
year.
59
Discussion
It is acceptable to assume a birth ratio of 50:50 of male and female leverets. The adult female
proportion of hares in the sample was significantly larger then the proportion of adult males.
Further, no males were determined to be more than 6 years of age, while the oldest female were
determined to be 8 years of age. The opposite were found in Abildegård et al. (1972), where the
majority of older animals was males. The hares from 1972 came from a small island population,
with no mammal-predators such as red fox (Vulpus vulpus) and pine martens (Martes martes). The
daily covered distances for males are larger than for females (Rühe & Hohman, 2004). If this
exposes the males to a higher predation-risk by mammal-predators, it could explain the observed
differences in the present study and Abildgård et al. (1972). A previous study in Poland has found
similar results as the present study, with no male hares of more than 6 years of age (Pielowski et al.,
1976).
The adult females were heavier than adult males, the same has been found in previous Danish study
(Hansen, 1991, A). The observed differences in weight and length between hares colleted from the
island Hjelm and the other locations could be a combined result of low predation rates and intra-
specific competition. There are no foxes on the island of Hjelm to remove less fit animals from the
population. The same is true for the hares collected on the island of Bornholm. The hares from
Bornholm do not show reduced weight or length. Therefore the absence of fox-predation on the
island of Hjelm can not be the sole factor causing the reduced weight observed. Compared to the
other locations population density (79.4 hares per km2) (Wincentzt, in prep) was extremely high at
Hjelm, combined with the confined area (63 ha) this may result in a high intra-specific competition
between hares on the island.
Compared to previous studies, a slightly lower percentage of the adult females were determined to
be reproductively active (Hansen, 1991, A; Peroux, 1995; Marboutin et al., 2003; Smith et al., 2005
, A). The mean number of leverets per adult female were low compared to what was found in
France (Marboutin & Peroux, 1995; Marboutin et al., 2003). A longer reproductive season and as a
result a higher number of litters could explain the observed differences. Hansen (1991, A) found the
number of leverets per female to be in the same range as present study.
60
The proportion of juveniles in the aged animals at the 11 locations, are comparable to previous
studies in Denmark (Abildsgård et al., 1972; Hansen, 1991, A; Hansen, 1994; Marboutin et al.,
2003; Smith et al., 2005, A). The low proportion of juveniles at Borris the juvenile, could be a result
of selective shooting, where hunters avoid shooting small individuals (personal comment, contact-
person from Borris). Also the Borris location had up to 20 fox-dens with fox-litters each year
(personal comment, contact-person from Borris). With a fox diet consisting of up to 50 % hares
(Goszcynski et al., 1992), this would result in a massive predation on leverets and juvenile hares.
Leaving a low number of juveniles available to hunters at the Borris population.
Studies from France have estimated the survival-rate of leverets from birth to the hunting season to
range from 25% to 50% (Pepin, 1989) and 14-29 % (Marboutin et al., 2003). The study areas that
Pepin (1989) investigated were all crop areas, while Marboutin et al. (2003) investigated both crop
and pasture farmland. The estimated leveret survival in the present study exceeded the leveret
survival estimated by Marboutin (2003).
The location with the highest leveret survival rate is Salling Planteskole, this area consists of
primarily small biotopes and fallow land, and some fields with crop. The mix of fields with crop
and many small biotopes, along with a minuscule use of agricultural machinery, could explain the
high estimated leveret survival-rate. At the other end of the scale is the Borris location with the
lowest leveret survival-rate. This location is a military training territory with no arable land. which
could result in a shortage of suitable food for the leverets, during summer (Hansen, 1991B).
Combined with the above mentioned high number of fox dens in the area, this could result in low
leveret survival. The adult survival-rates were expected to be higher than the juvenile survival-rates,
but this was not the case. An explanation could be the already mentioned human factor, that
hunters avoid shooting the obviously smaller hares. Thereby biasing the proportion of juvenile
animals in the hunting bag record.
Part of the data used in the generated models was gathered from questionnaires and telephone-
interviews with contact-persons from each location. One of the main disadvantages of
questionnaires is the potential lack of accurate detail in the collected data (Vaughan et al., 2003). In
the present fox, and hare densities were calculated from hunting records, and not from actually
counted numbers of fox and hares. Interpretations from hunting records are difficult (Marboutin et
61
al., 2003). The hunting records obtained in the present study were at times not elaborate enough to
give all wanted parameters, such as number of hunters, hours spent hunting and/or area covered by
the hunters. Also no measure of the hunters hunting skills (accuracy of fire) was provided. In future
studies it is recommended that game-density should be obtained by other means or accuracy of fire
should be obtained by the comparing number of shots fired to number the of game killed and
collected.
Several of the contact-persons stated that great effort was taken each year to keep the fox population
at a minimum. This was done not only by hunting but also by control actions, such as culling
juvenile foxes during summer or by destroying natural fox-dens in the area. The foxes removed
during summer were not recorded in hunting records, and therefore not included in the present
study. Not only the above distorts the calculated fox-densities, it could also mean that fox-density in
several of the locations are to low to have any impact on hare mortality.
Measurement of traffic intensity was estimated by contact-persons to be low, medium or high. It
would have been desirable to have the actual count of yearly traffic from the roads in question.
The percentage of area used for crop and pasture was considered an accurate measurement, as the
majority of contact-persons had the precious numbers on the local land use.
The age of females was included in the reduced model for reproductive success as expected.
European hare fertility has previously been found to be significantly higher in older females
compared to juveniles (Frylestam, 1980; Marboutin et al., 2003). In a resent study from Australia
the opposite was found, here juvenile females showed higher fertility-rates than females of more
than one year of age (Stott et al., 2006). The climate in Australia is profoundly different than the
climate in most of Europe, which might have induced the observed differences in reproduction
success. Weight can be an indicator of fitness, and the number of litters have been found to be
positively correlated to size and body weight of female hares (Fryletam, unpubl.). In the present
study, the weight was measured after the reproduction period. At this time of year a high number of
offspring may have reduced the female’s fat-deposition, possibly leaving females with high
reproduction success, weighing less than infertile females.
Fox predation have found been found to reduce up to 17 % of leverets during the spring season and
account for up to 53 % of total winter mortality in hares (Goszczynski et al., 1992). A high
population density of foxes therefore reduces the proportion of juvenile hares in the hunting bag. A
62
previous study has found the number of foxes culled in one year to have a marked negative effect
on number of hares culled the following year (Schmidt et al., 2004). The fox density values were
calculated as a mean of the years 2000-2005. Therefore a delayed affect as found in Schmidt et al.
(2004) would not be apparent in present study. Fox density were included in the reduced model for
leveret-survival as expected
The European hare diet mainly consist of cultivated crop and grasses (Hansen et al. 1990; Reichlin
et al., 2006) therefore % crop and pasture was included in the model, as expected. Several studies
have found the loss of crop, grasses and landscape diversity to be the main reason for a decline in
hare population (Edwards et al., 2000; Tapper & Barnes, 1986; Smith et al., 2004). Also hares
prefer to feed on short crops and their preference for cereal decline as crops developed beyond the
tillering stage (Tapper & Barnes, 1986). Leaving large areas with winter crops without nutritional
value for the hare during the summer. In the present study only the percentage of land-use was
known, no value for landscape diversity was available. Landscape diversity might prove to be a
more useful parameter than land-use, and thereby increase the models explanatory value. No
difference in food quality of pastural and arable landscape has been found (Smith et al., 2005, B). It
has been suggested that pastural landscape is more wet then arable, thereby increasing the hares
costs for thermoregulation and causing higher transmission of diseases (Smith et al., 2005, B).
Which would make hares in pastural landscape more vulnerable to predation than hares in arable
landscape.
During the last 4 decades more attention has been paid to wildlife road mortality. Traffic has been
concluded to overtake hunting as the leading direct cause of vertebrate mortality on land (Foreman
et al., 1998). Traffic intensity was therefore expected to be included in the reduced model, but this
was not the case, possible due to the lack of accurate data of traffic intensity at the locations. The
Danish traffic mortality in hares was quantified by Hansen (1982) for the years 1958, 1965 and
1980, during these years Hansen (1982) estimated the number of hares killed in traffic in Denmark
to have increased from around 17.000 to more than 77.000 per years. The number of hares killed in
traffic increased with traffic intensity, despite the reduction of hare-density found in hunting bag
records for the four decades. With an yearly increase of 3.9 % in Danish traffic intensity since 1980
(www.vejdiraktoratet.dk), the expected number of hares killed in traffic in 2003 would be around
146.500, more than twice the number recorded in the Danish bag records for 2003
63
(www.vildtudbytte.dk/dmu3.asp). It seems likely that road mortality for hares in Denmark in fact
can have an impact on population-level. Traffic should therefore be considered an area of concern,
on equal terms with agricultural intensification and increasing number of predators. Traffic intensity
was therefore expected to be included in the reduced model for stage specific survival, but this was
not the case.
No previous studies have been made on fat-depositions influence on survival. Therefore fat-
deposition will receive no further comment.
Conclusion The overall explanatory value of the reduced model for age was not as high as expected. With the
stochastic processes accounting for more than 80 %, the model can not be used for predicting
purposes. The failure of the model is expected to be a combination of inaccurate data and/or
variables not included in the model, such as food quality and precise numbers of predators besides
foxes at each location. Also the model would probably have been improved if locations with very
low hare-density had been included in the study.
There is no doubt that the European hares populations are experiencing a decline in numbers.
Several suggestions have been made on how to reverse the decline. Most studies agree that further
intensification of farming, resulting in homogeneity of the landscape is not the way to go about it
(Vaughan et al, 2003; Lundstöm-Gilliéron & Schlaepfer, 2003; Tapper & Barnes, 1986; Smith et al,
2005, A).
There is some doubt to the question of where the actual problem lies. Some have appointed low
recruitment levels, caused by low reproduction success (Hansen & Hartmann, 1994) to be the main
factor, others suggest that populations growth is more sensitive to adult survival (Marboutin &
Peroux, 1995). This suggests that declining populations are more sensitive to hunting than stable
populations (Smith et al., 2005, A). Others have found the decline to be mainly attributed to
predation by red fox (Schmidt et al., 2004).
Habitat management has been declared a possible solution to the problem, with implementation of
habitat diversity at all scales, within landscape, farms and fields. This could result in high-quality
64
resources in terms of food and cover from bad weather and predation throughout the year (Tapper &
Barnes, 1986; Smith et al., 2005, A). Creating more extensive livestock systems, e.g. with
traditional haymaking instead of frequently cutting grasses for silage, could reduce the number of
leverets killed in machinery.
In order to optimize landscape for hare populations, pastural landscapes should contain some
woodland and fields with arable crop (< 20 ha) and arable farmers should include wheat, beet and
fallow land in their rotations (Vaughan et al., 2003). Also a reduction of agricultural-areas used for
winter crop could increase the amount of food available to the European hare during mid- and late
summer.
At the same time it is suspected that an intrinsic factor not yet understood, may also drive the hares
population dynamics (Smith et al., 2004).
Acknowledgement
Danmarks Miljøundersøgelser (NERI) for funding the project. The contact-persons from each of the
11 locations for completing the questionnaire and telephone-interviews. Gösta Nachman and
Tommy Asferg for criticism on previous drafts. Trine-Lee Wincentz Jensen for general comments
on the project. Preparation and sectioning of mandibles were done by Jette Barlach and Sussi
Madsen, from the Royal Dental College, University of Aarhus, to whom I am grateful for their
work.
References
Abildsgård, F., Andersen, J. & Barndorff-Nielsen, O. 1972. The hare population (Lepus
europaeus Pallas) of Illumø island, Danmark. A report on the analysis of the data from 1957-1970.
Danish review of game biology, 6 (5): 1-32.
Bray, Y., Marboutin, E., Peroux, R. & Ferron, J. 2003. Reliability of stained placental scar
counts in European hare. Wildlife Society Bulletin, 31: 237-246.
65
Broekhuizen, S. 1982. Studies on the population ecology of hares in the Netherlands. Research
Institute for Nature management, Arnhem, Netherlands.
Edwards, P.J., Fletcher, M.R. & Berny, P. 2000. Review of the factors affecting the decline of
the European brown hare, Lepus europaeus (Pallas, 1778) and the use of wildlife incident data to
evaluate the significant of paraquat. Agriculture, Ecosystems and Environment, 79: 95-103.
Foreman, R. T., Sperling, D., Bissonette, J.A., Clevenger, A.P., Cutshall, C.D., Dale, V.H.,
Fahrig, L., France, R., Goldman, C.R., Heanue, K., Jones, J.A., Swanson, F.J., Turrentine, T.
& Winter, T.C. 2003. Road ecology. Science and Solutions. Island press, Washington: 1-481
Frylestam, B. 1980. Reproduction in the European hare in southern Sweden. Holarctic Ecology, 3:
74-80.
Goszczynski, J. & Wasilenwski, M. 1992. Predation of foxes on a hare population in central
Poland. Acta Theriologica, 37: 329-338.
Hackländer, K., Miedler, S., Berglböck, C. & Zenker, W. 2002. The assessment of female
reproduction and gestational age in European hares (Lepus europaeus) Using ultrasonography.
Mammalian biology, 68: 187-191.
Haerer, G., Nicolet, J., Barcciarini, L., Gottstein, B. & Giacometti, M. 2001. Causes of
mortality, zoonoses and reproductive performance in European brown hare in Switzerland.
Schweizer Archive für tierheillkunde, 143: 193-201.
Hansen, Sørensen & Daugård, 1989. Bestandstørrelse og afgrødevalg hos hare (Lepus
europaeus). Landbrugsministeriets Vildforvaltning. Rapport fra Vildtbiologisk Station : 1-12.
Hansen, K., Jessen Holm, M. & Simonsen, N.H. 1990. Harens (Lepus europaeus) fødevalg på
landbrugsarealer. Danmarks Miljøundersøgelser. Intern rapport afd. fra flora og faunaøkologi: 1-32.
66
Hansen, K. 1991 A. Overlevelse og reproduktion i en dansk harebestand. Danmarks
Miljøundersøgelser. Faglig rapport fra DMU, 30: 1-36.
Hansen, K. 1991 B. Impact of modern farming on food supply of hare (Lepus europaeus, Pallas)
during the summer period. Proceeding of the I European Congress of Mammalogy, Lisboa, March
1991: 1-13.
Hansen, K. & Hartmann, P. 1994. Unge harer i jagtudbyttet. Faglig rapport fra DMU, 125: 1-120.
Hansen, L. 1982. Trafikdræbte dyr i Denmark. Dansk Ornitologisk Forenings Tidsskrift, 76: 97-
110.
Klansek, E., Kalivodová, E., Simonovic, V. & Kürthy, A. 1998. Landscape-ecological evaluation
of the flood plain of the river March (Morava) with regard to hare (Lepus europaeus Pallas) and roe
dear (Capreolus capreolus L.). Ekológia (Bratislava), 17: 201-207.
Lundström-Gilierón, C. & Schlaepfer, R. 2003. Hare abundance as an indicator for urbanisation
and intensification of agriculture in Western Europe. Ecological Modelling, 168: 283-301.
Marboutin, E. & Peroux, R. 1995. Survival pattern of European hare in a decreasing population.
Journal of Applied Ecology, 32: 809-816.
Marboutin, E., Bray, Y., Peroux, R., Mauvy, B. & Lartiges, A. 2003. Population dynamics in
European hare: breeding parameters and sustainable harvest rates. Journal of Applied Ecology, 40:
580-591.
Mitchell-Jones, A.J., Amori, G., Bogdanowicz, W., Krystufek, B., Reijnders, P.J.,
Spitzenberger, F., Stubbe, M., Thissen, J.B.M., Vohralik, V. & Zima, J. 1999. The atlas of
European mammals. ACADEMIC PRESS. T & AD poyser Ltd.: 1-484.
Morris, P. 1972. A review of mammalian age determination methods. Mammal Review, 2: 69-
104.
67
Pepin, D. 1989. Variation in survival of brown hare (Lepus europaeus) leverets from different
farmland areas in the Paris basin. Journal of Applied Ecology, 26: 13-23.
Péroux, R. 1995. Speciale liévre d Èuropa. Lóffice National de la Chasse, Paris: 1-204.
Pielowski, Z. 1976. Number of young born and dynamics of European hare population. In: Ecology
and management of European hare populations. Polish Hunting association, Warsaw: 75-78.
Reichlin, T., Klansek, E. & Hackländer, K. 2006. Diet selection by hares (Lepus europaeus) in
arable land and its implication for habitat management. European Journal of Wildlife Research, 52:
109-118.
Reynolds, J.C. & Tapper, S.C. 1995. Predation by fox Vulpus vulpus o brown hares Lepus
europaeus in the central southern England, and its potential impact on annual population growth.
Wildlife Biology, 1(3): 145-158.
Rühe, F. & Hohmann, U. 2004. Seasonal locomotion and home range characteristics of European
hares (Lepus europaeus) in an arable region in central Germany. European Journal of Wildlife
Research, 50: 101-111.
Schmidt, N.M., Asferg, T. & Forchhammer, M.C. 2004. Long-term patterns in European brown
hare population dynamics in Denmark: Effects of agriculture, predation and climate. BMC Ecology,
4: 1-7.
Smith, R.K., Jennings, N.V., Robinson, A. & Harris, S. 2004. Conservation of European hares
Lepus europaeus in Britain: is increasing habitat heterogeneity in farmland the answer?. Journal of
Applied Ecology, 41: 1092-1102.
Smith, R.K., Jennings, N.V. & Harris, S. 2005, A. A quantitative analysis of the abundance and
demography of European hares Lepus europaeus in relation to habitat type, intensity of agriculture
and climate. Mammal Review. 35: 1-24.
68
Smith, R.K., Jenning, N.V., Tataruch, F., Hackländer, K. & Harris, S. 2005, B. Vegetation
quality and habitat selection by European hares Lepus europaeus in a pastural landscape. Acta
Theriologica, 50: 391-404.
Stoltze, M. 1997. Gulliste 1997 over plante og dyr I Danmark. Miljø og energiministeriet,
Danmarks Miljøundersøgelser og skov- og naturstyrelsen: 1-48.
Stott, P. & Harris, S. 2006. Demographical of European hare (Lepus europaeus) in the
Mediterranean climate zone of Australia. Mammalian Biology, 71: 21.-226.
Tapper, S.C. & Parsons N. 1984. The changing status of the Brown hare (Lepus capensis L.) in
Britain. Mammal review. 14: 57-70
Tapper, S.C. & Barnes, R.F. 1986. Influence of farming practice on the ecology of the brown hare
(Lepus europaeus). Journal of Applied Ecology, 23: 39-52.
Vaughan, N., Lucas, E., Harris, S. & White, P.C.L. 2003. Habitat association of European hares
Lepus europaeus in England and Wales: implications for farmland management. Journal of Applied
Ecology, 40: 163-175.
69
Appendix 1
Figure 1: Distribution of the 11 locations in Denmark were the hares were culled
Vennerslund
Pandebjerg
Gl. Kirstineberg Orebygård
Borreby
Bornholm
Hjelm Giesegård
Salling planteskole
Borris
Magrethe kog
70
Table 1: Sex distribution at the 11 locations Study area Juvenile Adult Total (N) Female Male Female Male Bornholm 7 5 5 4 21 Borreby 14 13 22 8 57 Borris 1 5 4 0 10 Giesegård 2 8 8 2 20 Gl. Kirstineberg 4 3 3 1 11 Hjelm 4 4 4 2 14 Margrethe kog 5 4 1 10 20 Orebygård 16 6 11 9 42 Pandebjerg 7 12 26 9 54 Salling plantes. 3 2 1 4 10 Vennerslund 11 21 30 11 73 Total (N) 74 83 115 60 332
71
Table 2: Weight distribution juvenile females (different letter indicate significant difference in mean weight) (αααα = 0.05) Name of study area
Juvenile females
(g) std N Tukey-test
Borris 3841.40 1 A Gl. Kirstineberg 3827.88 483.25 4 A Pandebjerg 3626.76 477.91 7 A Giesegård 3408.00 195.16 2 A Bornholm 3394.21 779.20 7 A Borreby 3257.36 482.98 14 A Orebygård 3226.14 707.99 16 A Vennerslund 3063.54 557.96 11 A Margrethe Kog 2774.84 729.64 5 AB Salling planteskole 2611.93 830.77 3 AB Hjelm 1652.88 285.70 4 B Table 3: Weight distribution juvenile males (different letter indicate significant difference in mean weight) (αααα = 0.05) Name of study area
Juvenile males
(g) std N Tukey-
test Gl. Kirstineberg 3856.00 1 A Orebygård 3505.21 618.03 9 A Borreby 3426.11 670.66 8 AB Vennerslund 3317.06 558.82 11 ABC Giesegård 3307.50 369.82 2 ABC Pandebjerg 3198.97 279.57 9 ABC Bornholm 3179.30 287.96 4 ABC Margrethe Kog 3077.96 283.52 10 ABC Salling planteskole 2443.38 656.65 4 C Hjelm 2298.25 274.29 2 BC Borris 0
72
Table 4: Weight distribution adult females (different letter indicate significant difference in mean weight) (αααα = 0.05) Name of study area
Adult Females
(g) std N Tukey-
test Gl. Kirstineberg 4306.43 341.86 3 A Borris 4296.18 274.58 4 A Bornholm 4221.34 393.82 5 A Salling planteskole 4213.00 1 A Orebygård 4147.66 287.44 11 A Vennerslund 4135.21 433.92 30 A Pandebjerg 4114.92 412.93 26 A Borreby 4103.63 450.84 22 A Giesegård 4094.13 231.05 8 AB Margrethe Kog 4030.60 1 AB Hjelm 3046.58 753.12 4 B Table 5: Weight distribution adult males (different letter indicate significant difference in mean weight) (αααα = 0.05) Name of study area
Adult males
(g) std N Tukey-
test Bornholm 3959.88 295.77 5 A Gl. Kirstineberg 3945.20 707.93 3 A Orebygård 3914.72 374.96 5 A Borris 3877.94 97.03 5 A Vennerslund 3842.07 259.23 22 A Borreby 3836.85 164.01 13 A Pandebjerg 3808.80 242.34 12 A Giesegård 3761.75 702.59 8 A Salling planteskole 3591.70 300.38 2 A Margrethe Kog 3488.56 497.19 4 A Hjelm 2731.15 646.06 4 B
73
Table 6: Age-related productivity (number of placental scar)
Age
Juv. 1-2. 2-3. 3-4. 4-5. 5-6. 6-7. <7 No age Total Total*
Examined (N) 8 24 29 22 12 6 3 2 7 113 105 Examined (%) 10.8 80 96.7 95.7 100 100 100 100 77.8 59.8 91.3 Females with scar (%) 12.5 79.2 75.9 68.2 100 66.7 66.7 100 28.6 69.9 74.3 Number of scars per examined female (N) 1.1 8.1 7.2 6.1 11.8 6.3 5.3 12.5 1.8 6.9 7.4 Number of scar per reproductivly active females (N) 9 10.5 10.3 9.6 11.8 12.5 8 12.5 11 10.5 10.6
Females produced per female (N) 0.6 4.1 3.6 3 5.9 3.1 2.7 6.3 0.9 3.4 3.7 * Age groups leveret and juvenile not included.
74
Table 7: Reproductive success at the 11 locations
Name of location N % Reproductively
active Leverets per
female Borris 3 100.0 14.0 Margrethe Kog 1 100.0 14.0 Pandebjerg 24 83.3 9.2 Vennerslund 27 96.3 8.7 Orebygård 11 72.7 8.7 Hjelm 2 100.0 8.5 Total 109 74.3 7.3 Overgård 4 75.0 5.8 Gl. Kirstineberg 3 100.0 5.5 Borreby 22 45.5 4.2 Giesegård 7 42.9 3.3 Bornholm 4 25.0 3.3 Salling planteskole 1 100.0 3.0
75
Table 8: Mean age and age distribution at the 11 locations
Name of location Mean age
Estimated age
distribution 0 1 2 3 4 5 6 >6 N Years Std N % N % N % N % N % N % N % N %
Vennerslund 74 1.7 1.12 22 29.7 17 23.0 14 18.9 12 16.2 4 5.4 3 4.1 1 1.4 1 1.4 Borreby 55 1.5 1.55 22 40.0 9 16.4 9 16.4 9 16.4 3 5.5 3 5.5
Pandebjerg 53 1.7 1.6 16 30.2 11 20.8 9 17,0 10 18.9 5 9.4 2 3.8 Orebygård 39 0.9 1.67 25 64.1 6 15.4 4 10.3 1 2.6 1 2.6 1 2.6 1 2.6
Margrethe kog 20 0.4 0.75 15 75.0 4 20.0 1 5.0 Bornholm 20 0.6 0.82 11 55.0 7 35.0 1 5.0 1 5.0 Giesegård 15 1.6 1.12 4 26.7 1 6.7 7 46.7 3 20,0
Hjelm 14 0.8 0.89 6 42.9 6 42.9 1 7.1 1 7.1 Gl. Kirstineberg 11 0.7 0.79 5 45.5 4 36.4 2 18.2
Salling pl. 10 0.7 1.25 7 70.0 1 10.0 2 20.0 Borris 9 2.0 1.12 1 11.1 1 11.1 5 55.6 1 11.1 1 11.1 Total 320 1.3 1.5 134 41.9 67 20.9 52 16.3 41 12.8 14 4.4 7 2.2 3 0.9 2 0.6
76
Figure 2: Mean age at the 11 locations, different letter indicate significant difference in mean age (αααα = 0.05).
Mean age
-2
-1
0
1
2
3
4
Borris Pandebjerg Vennerslund Giesegård Borreby Orebygård Hjelm Gl.Kirstineberg
Sallingplantes.
Bornholm Margrethekog
Name of study area
Age
(ye
ars)
ABABC A A ABC
BABC ABC ABC ABC
C
77
Table 9: P-value for Kolmogorov-smirnov test for difference in age distribution.
Name of location Vennerslund Borreby Pandebjerg Orebygård Bornholm Giesegård Margrethe Kog Hjelm Anholt Salling pl. Gl Kirstineberg
Vennerslund 0.491 0.971 0 0 0.399 0 0.006 0.052 0.002 0.02 Borreby 0.947 0.038 0.025 0.503 0.001 0.104 0.086 0.004 0.078 Pandebjerg 0.012 0.002 0.336 0 0.018 0.092 0.005 0.032 Orebygård 0.255 0.013 0.044 0.36 0.172 0.016 0.262 Bornholm 0.004 0.771 0.998 0.179 0.315 0.892 Giesegård 0.001 0.021 0.851 0.102 0.033 Margrethe kog 0.3 0.095 0.315 0.489 Hjelm 0.363 0.587 1 Anholt 0.675 0.574 Salling pl. 0.829
Gl. Kirstineberg
78
Table 10-21: Lifetables for the 11 locations Lifetable for Vennerslund Smoothed
Age Frequency Survivel Mortality Mortality rate Survival rate Survivel Mortality Mortality rate Survival ratex N ax lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) lx dx qx (dx/lx) px (1-qx) 0 226 300 1.00 0.75 0.75 0.25 0.00 0.00 1.00 0.75 0.75 0.25
0.5 22 74 0.25 0.07 0.30 0.70 -1.40 -1.40 0.25 0.07 0.30 0.70 1 17 52 0.17 0.06 0.33 0.67 -1.75 -1.52 0.22 0.11 0.49 0.51 2 14 35 0.12 0.05 0.40 0.60 -2.15 -2.20 0.11 0.05 0.49 0.51 3 12 21 0.07 0.04 0.57 0.43 -2.66 -2.87 0.06 0.03 0.49 0.51 4 4 9 0.03 0.01 0.44 0.56 -3.51 -3.55 0.03 0.01 0.49 0.51 5 3 5 0.02 0.01 0.60 0.40 -4.09 -4.23 0.01 0.01 0.49 0.51 6 1 2 0.01 0.00 0.50 0.50 -5.01 -4.91 0.01 0.00 0.49 0.51 7 1 1 0.00 0.00 1.00 0.00 -5.70 -5.59 0.00 0.00 1.00 0.00
I alt 300
Lifetable for Borreby Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival ratex N ax lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) lx dx qx (dx/lx) px (1-qx) 0 69 124 1.00 0.73 0.73 0.27 0.00 0.00 1.00 0.73 0.73 0.27
0.5 22 55 0.44 0.25 0.56 0.44 -0.81 -1.40 0.44 0.25 0.56 0.44 1 9 33 0.27 0.15 0.55 0.45 -1.32 -0.93 0.39 0.18 0.46 0.54 2 9 24 0.19 0.15 0.75 0.25 -1.64 -1.55 0.21 0.10 0.46 0.54 3 9 15 0.12 0.10 0.80 0.20 -2.11 -2.17 0.11 0.05 0.46 0.54 4 3 6 0.05 0.05 1.00 0.00 -3.03 -2.79 0.06 0.03 0.46 0.54 5 3 3 0.02 0.02 1.00 0.00 -3.72 -3.41 0.03 0.03 1.00 0.00
I alt 124
79
Lifetable for Pandebjerg Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival ratex N ax lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 170 223 1.00 0.76 0.76 0.24 0.00 0.00 1.00 0.76 0.76 0.24
0.5 16 53 0.24 0.07 0.30 0.70 -1.44 -1.40 0.24 0.07 0.30 0.70 1 11 37 0.17 0.05 0.30 0.70 -1.80 -1.51 0.22 0.11 0.48 0.52 2 9 26 0.12 0.04 0.35 0.65 -2.15 -2.17 0.11 0.06 0.48 0.52 3 10 17 0.08 0.04 0.59 0.41 -2.57 -2.83 0.06 0.03 0.48 0.52 4 5 7 0.03 0.02 0.71 0.29 -3.46 -3.49 0.03 0.01 0.48 0.52 5 0 2 0.01 0.00 0.00 1.00 -4.71 -4.15 0.02 0.01 0.48 0.52 6 2 2 0.01 0.01 1.00 0.00 -4.71 -4.82 0.01 0.01 1.00 0.00
I alt 223
Lifetable for Orebygård Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) lx dx qx (dx/lx) px (1-qx) 0 61 100 1.00 0.61 0.61 0.39 0.00 0.00 1.00 0.61 0.61 0.39
0.5 25 39 0.39 0.25 0.64 0.36 -0.94 -1.40 0.39 0.25 0.64 0.36 1 6 14 0.14 0.06 0.43 0.57 -1.97 -1.94 0.14 0.05 0.33 0.67 2 4 8 0.08 0.04 0.50 0.50 -2.53 -2.34 0.10 0.03 0.33 0.67 3 1 4 0.04 0.01 0.25 0.75 -3.22 -2.73 0.07 0.02 0.33 0.67 4 1 3 0.03 0.01 0.33 0.67 -3.51 -3.13 0.04 0.01 0.33 0.67 5 1 2 0.02 0.01 0.50 0.50 -3.91 -3.53 0.03 0.01 0.33 0.67 6 0 1 0.01 0.00 0.00 1.00 -4.61 -3.93 0.02 0.01 0.33 0.67 7 0 1 0.01 0.01 1.00 0.00 -4.61 -4.33 0.01 0.00 0.33 0.67 8 1 1 0.01 0.01 1.00 0.00 -4.61 -4.72 0.01 0.01 1.00 0.00
I alt 100
80
Lifetable for Margrethe kog Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 35 55 1.00 0.64 0.64 0.36 0.00 0.00 1.00 0.64 0.64 0.36
0.5 15 20 0.36 0.27 0.75 0.25 -1.01 -1.40 0.36 0.27 0.75 0.25 1 4 5 0.09 0.07 0.80 0.20 -2.40 -2.67 0.07 0.04 0.55 0.45 2 0 1 0.02 0.00 0.00 1.00 -4.01 -3.47 0.03 0.02 0.55 0.45 3 1 1 0.02 0.02 1.00 0.00 -4.01 -4.28 0.01 0.01 1.00 0.00
I alt 55
Lifetable for Bornholm Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 15 35 1.00 0.43 0.43 0.57 0.00 0.00 1.00 0.42 0.42 0.58
0.5 11 20 0.57 0.31 0.55 0.45 -0.56 -0.54 0.58 0.31 0.52 0.48 1 7 9 0.26 0.20 0.78 0.22 -1.36 -1.49 0.22 0.15 0.67 0.33 2 1 2 0.06 0.03 0.50 0.50 -2.86 -2.59 0.07 0.05 0.67 0.33 3 1 1 0.03 0.03 1.00 0.00 -3.56 -3.69 0.02 0.02 1.00 0.00
I alt 35
81
Lifetable for Giesegård
Smoothed Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate
x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 23 38 1.00 0.61 0.61 0.39 0.00 0.00 1.00 0.61 0.61 0.39
0.5 4 15 0.39 0.11 0.27 0.73 -0.93 -0.93 0.39 0.11 0.27 0.73 1 1 11 0.29 0.03 0.09 0.91 -1.24 -1.05 0.35 0.17 0.48 0.52 2 7 10 0.26 0.18 0.70 0.30 -1.34 -1.70 0.18 0.09 0.48 0.52 3 3 3 0.08 0.08 1.00 0.00 -2.54 -2.35 0.09 0.09 1.00 0.00
I alt 38
Lifetable for Hjelm
Smoothed Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate
x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 34 50 1.00 0.68 0.68 0.32 0.00 0.00 1.00 0.68 0.68 0.32
0.5 6 16 0.32 0.12 0.38 0.63 -1.14 -1.14 0.32 0.12 0.38 0.63 1 6 10 0.20 0.12 0.60 0.40 -1.61 -1.71 0.18 0.08 0.45 0.55 2 1 4 0.08 0.02 0.25 0.75 -2.53 -2.32 0.10 0.04 0.45 0.55 3 3 3 0.06 0.06 1.00 0.00 -2.81 -2.92 0.05 0.05 1.00 0.00
I alt 50
Lifetable for Gl. Kirstineberg Smoothed
Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 23 34 1.00 0.68 0.68 0.32 0.00 0.00 1.00 0.68 0.68 0.32
0.5 5 11 0.32 0.15 0.45 0.55 -1.13 -1.13 0.32 0.15 0.45 0.55 1 4 6 0.18 0.12 0.67 0.33 -1.73 -1.73 0.18 0.12 0.67 0.33 2 2 2 0.06 0.06 1.00 0.00 -2.83 -2.83 0.06 0.06 1.00 0.00
I alt 34
82
Lifetable for Salling pl. Skole
Smoothed Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate
x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 5 15 1.00 0.33 0.33 0.67 0.00 0.00 1.00 0.33 0.33 0.67
0.5 7 10 0.67 0.47 0.70 0.30 -0.41 -0.41 0.67 0.47 0.70 0.30 1 1 3 0.20 0.07 0.33 0.67 -1.61 -1.68 0.19 0.03 0.18 0.82 2 0 2 0.13 0.00 0.00 1.00 -2.01 -1.88 0.15 0.03 0.18 0.82 3 2 2 0.13 0.13 1.00 0.00 -2.01 -2.08 0.12 0.12 1.00 0.00
I alt 15
Lifetable for Borris
Smoothed Age Frequency Survival Mortality Mortality rate Survival rate Survival Mortality Mortality rate Survival rate
x N ax Lx dx qx (dx/lx) px (1-qx) ln(lx) ln(lx) Lx dx qx (dx/lx) px (1-qx) 0 63 72 1.00 0.88 0.88 0.13 0.00 0.00 1.00 0.88 0.88 0.13
0.5 1 9 0.13 0.01 0.11 0.89 -2.08 -2.08 0.13 0.01 0.11 0.89 1 1 8 0.11 0.01 0.13 0.88 -2.20 -1.97 0.14 0.07 0.53 0.47 2 5 7 0.10 0.07 0.71 0.29 -2.33 -2.72 0.07 0.03 0.53 0.47 3 1 2 0.03 0.01 0.50 0.50 -3.58 -3.47 0.03 0.02 0.53 0.47 4 1 1 0.01 0.01 1.00 0.00 -4.28 -4.22 0.01 0.01 1.00 0.00
I alt 72
83
Appendix 2
GENMOD model for number of placental scars Parameters included in the model; Number of scars g(x): quantitative Age (A): quantitative Weight (W): quantitative Percentage of area used for crop and pasture (% Crop and pasture): quantitative Full model; Type III Analysis Source df Chi-square Pr>chisq Age 1 14.11 **0.0002 Weight 1 7.55 **0.0060 % Crop and pasture
1 0.86 0.3548
Reduced model; Type III Analysis Source df Chi-square Pr>chisq Age 1 15.26 ***<.0001
84
Appendix 3
GLM model for stage specific survival-rates Parameters in the model; Age specific survival-rate f(x) Fox desity (X5): quantitative Hare desity (X6): quantitative % Crop and pasture without stock (X7): quantitative Fat-deposition (X8. X9 X10 and X11): qualitative Traffic intensity (X12. X13 and X14): qualitative Full model; R2 = 0.152 Source Type III SS df MS F P Model 1.373 8 0.172 ***6.79 <.0001
Fox density 0.182 1 0.182 ***8.92 0.007
Hare density 0.023 1 0.226 **8.92 0.003 % Crop and pasture
0.509 1 0.509 ***20.12 <.0001
Fat-deposition 0.015 3 0.005 0.20 0.895 Traffic intensity
0.130 2 0.065 2.58 0.065
Error 7.664 303 0.025 Total 9.039 311
85
Reduced model; R2 = 0.136 Source Type III SS df MS F P Model 1.230 3 0.410 ***16.17 <.0001 Fox density 0.183 1 0.183 **7.21 0.008 Hare density 0.259 1 0.259 **10.22 0.0015 % Crop and pasture
1.094 1 1.094 ***43.16 <.0001
Error 7.809 308 0.025 Total 9.039 311
![Dynamik sozialer Produktion [II]](https://img.dokumen.tips/doc/110x75/577d38d01a28ab3a6b988be2/dynamik-sozialer-produktion-ii.jpg)
