Overwintering Ecology of Wood Turtles (Glyptemys Insculpta) at the Species' Northern Range Limit

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Overwintering Ecology of Wood Turtles (Glyptemys Insculpta)at the Species Northern Range LimitAuthor(s) William F Greaves and Jacqueline D LitzgusSource Journal of Herpetology 41(1)32-40 2007Published By The Society for the Study of Amphibians and ReptilesDOI httpdxdoiorg1016700022-1511(2007)41[32OEOWTG]20CO2URL httpwwwbiooneorgdoifull1016700022-151128200729415B323AOEOWTG5D20CO3B2

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Overwintering Ecology of Wood Turtles (Glyptemys insculpta) at theSpeciesrsquo Northern Range Limit

WILLIAM F GREAVES AND JACQUELINE D LITZGUS1

Department of Biology Laurentian University Sudbury Ontario P3E 2C6 Canada

ABSTRACTmdashSeasonal variation in activity patterns of reptiles is accompanied by physiological and

behavioral adjustments that influence their ecology and life history and overwinter survival may be an

important factor limiting a speciesrsquo northern range extension A northern population of Wood Turtles

(Glyptemys insculpta) in Ontario Canada was surveyed in fall 2004 and a subset of adults was radio-tracked

every 7ndash12 days during the winter of 2004ndash2005 to examine thermal aspects of overwintering We predicted

that Wood Turtles would use hibernacula that protect them from freezing and predation Temperature data

loggers indicated that turtle body temperatures and hibernacula temperatures remained near 0uC from 2

December 2004 until 3 April 2005 During the same period air temperatures fluctuated substantially and

reached a maximum of 105uC (on 30 March 2005) and a minimum of less than 240uC (on 21 January 2005)

with a mean of 283uC Turtles did not select specific water temperatures nor did they use distinct structures

(eg root hollows logjams and holes in the riverbank) for overwintering but instead rested relatively

exposed on the riverbed at a depth of approximately 1 m and at a mean distance of 10 m from the riverbank

Surprisingly turtles made small movements during winter (01ndash100 m between radiolocations) typically

against the river current and in a direction parallel to the riverbank Average winter home-range size was

71 m2 Our findings raise questions about why turtles move during winter we suggest possible answers and

future lines of investigation to address these questions

Seasonal variation in activity patterns ofreptiles requires physiological and behavioraladjustments that influence both their ecologyand life history (Crawford 1991) This isespecially true for reptiles at northern latitudeswhere winter imposes harsh and unfavourableconditions for extended periods of time (StClair and Gregory 1990) The unpredictableconditions associated with seasonality at north-ern latitudes contribute to the observed de-crease in species diversity with increasinglatitude (Cloudsley-Thompson 1971) Mostreptiles tolerate cold winter temperatures andavoid mortality from freezing by overwinteringin thermally stable refugia (Gregory 1982Ultsch 1989) Aquatic turtles typically utilizesome form of aquatic medium as their thermalrefuge in winter (Brown and Brooks 1994Ultsch 2006) however temperatures withinhibernacula in northern climates can still ap-proach 0uC Because of decreased mobility fromlow temperatures turtles are at risk of mortalityfrom the inability to flee dangerous circum-stances such as predators or exposure toextreme temperatures from fluctuating waterlevels during overwintering (Brooks et al1991) Therefore the thermal suitability ofa turtle to its hibernaculum may be the most

important factor affecting the speciesrsquo over-wintering success (Gregory 1982) Thus turtlesmust use hibernacula with characteristics thatwill promote overwinter survival (Ultsch 19852006) including protection from predators andfreezing temperatures (Brown and Brooks1994)

Although the winter ecology of Wood Turtles(Glyptemys insculpta) has been described insouthern populations (eg Ernst 1986 Grahamand Forsberg 1991) there are no published dataon the overwintering ecology at the northernextreme of the speciesrsquo range Previous studieshave found that Wood Turtles in southernlocales overwinter in slow-moving streams thatdo not freeze over (Ernst et al 1994) Depend-ing on geographical region Wood Turtles beginoverwintering between late October and thefirst week of November (Harding and Bloomer1979 Ernst et al 1994) At the most northernlatitude studied to date (Quebec Canada46u389N) most turtles entered hibernation bythe first week of November (Arvisais et al2002) Hibernacula in more southern localesinclude deep pools under overhanging roots orlogs along a river muskrat burrows and inbeaver ponds (Ernst 1986) Generally WoodTurtles prefer streams with relatively highoxygen concentrations that do not freeze (Gra-ham and Forsberg 1991 Ernst et al 1994)which decreases the need for anaerobic activityduring overwintering (Ultsch and Jackson 19821 Corresponding Author E-mail jlitzguslaurentianca

Journal of Herpetology Vol 41 No 1 pp 32ndash40 2007Copyright 2007 Society for the Study of Amphibians and Reptiles

1985) In Massachusetts Wood Turtles havebeen observed resting on the bottom of streamsin 03ndash06 m deep water during winter (Grahamand Forsberg 1991) In New Jersey groups aslarge as 70 turtles overwintered together it wasspeculated that Wood Turtles in this locationwere hibernating communally as a result ofsocial structure and not because suitable hiber-nacula were a limited resource (Bloomer 1978)In Pennsylvania turtles used rivers that did notfreeze over and were 10ndash23 m deep (Ernst1986) The overwintering ecology of WoodTurtles at northern latitudes has not yet beendescribed despite the fact that overwintersurvival may be an important factor limitingthe northern range extent for the species

The objectives of the current study were todescribe hibernacula winter thermal ecologyand winter activity of Wood Turtles at thespeciesrsquo northern range limit We hypothesizedthat Wood Turtles would use hibernacula thatwould protect them from freezing and pre-dation We predicted that Wood Turtles woulduse the main river during winter to protectthem from freezing because the river would notfreeze because of the current as opposed toadjacent water bodies found at the study sitethat likely freeze over completely (eg beaverponds oxbows) We predicted that turtleswould use structures to protect them frompredation (eg root hollows log jams) Finallybecause the field site is at the northern extremeof the speciesrsquo range we predicted that turtleswould overwinter communally because suitablehibernacula are a limiting resource We exam-ined turtle body temperatures physical proper-ties of hibernacula (eg distance from shorewater depth temperatures duration of icecover) and communal hibernation and wemonitored overwinter survival Behavior andmovements during winter were examined usingradiotelemetry Description of habitat and ther-mal requirements during winter may helpunderstand factors limiting the speciesrsquo north-ern range extent (Ultsch and Jackson 1982 1985Ultsch 2006) Such data will also assist in thecreation and implementation of conservationprograms that set aside areas to help maintainviable populations of Wood Turtles which aredeclining in numbers throughout their range(Klemens 2000)

MATERIALS AND METHODS

Study SpeciesmdashThe Wood Turtle is a medium-sized (maximum shell length 234 cm) semi-aquatic freshwater turtle that is sparsely dis-tributed throughout its range in eastern NorthAmerica (Harding and Bloomer 1979 Ernst etal 1994) In Canada it is found in small

relatively isolated populations in Nova ScotiaNew Brunswick Quebec and Ontario (Ernst etal 1994) In Ontario Wood Turtle populationsare restricted primarily to Algonquin ProvincialPark (Brooks et al 1991) Huron County(Foscarini 1994) the Sault Ste Marie District (JTrottier pers comm 2005) and the SudburyDistrict (this study) In Canada Wood Turtlesare designated as a Species of Special Concernby the Committee of the Status of EndangeredWildlife in Canada (Litzgus and Brooks 1996)and as Endangered in Ontario by the Ministryof Natural Resources Wood Turtle populationsare declining as a result of habitat loss andcollection for the pet trade (Harding andBloomer 1979 Ernst et al 1994 Litzgus andBrooks 1996)

Study SitemdashThe study site is located ina relatively remote area of the Sudbury Districtof Ontario Canada (46uN 81uW) Winters aretypically long and cold lasting 5ndash6 months witha mean temperature of 283uC from Novemberto the end of March Summers are short andwarm lasting from late June to the end ofAugust with a mean temperature of 173uC(Environment Canada) Temperatures begindecreasing in September with the first snowfallusually occurring in October (W F Greavespers obs) Ice-off from most lakes in theSudbury District can occur from mid-April toearly May (W F Greaves pers obs)

The study site includes a 15-km section ofriver that flows through the Great Lakes-StLawrence forest region The name and exactlocation of the river is not given herein toprotect the Wood Turtle population frompoaching (Litzgus and Brooks 1996) Themeandering river ranges from 10ndash20 m in widthand is generally less than 2 m in depth Theriverbed substrate includes clay silt cobblesand boulders however sand is the mostprevalent substrate There are some humandisturbances along the river including smallresidences that may only be used in summeraccess roads and power lines The riverextending from the study site passes throughtownships aggregate extraction pits and log-ging areas hunting also occurs in the vicinity ofthe study site

SamplingmdashWe surveyed for Wood Turtlesfrom September to October 2004 Turtles werelocated and captured as researchers walked theriver and visually searched the riverbed log-jams root hollows and shorelines Three malesand two females were outfitted with 10-g radiotransmitters (Holohil Systems Ltd Carp ON)Radio tracking at the site in winter was difficultand constrained because of severe weathershort daylight hours and limited access to theremote site therefore only five turtles were

WINTER ECOLOGY OF WOOD TURTLES 33

outfitted with transmitters Radio transmitterswere wired and epoxied onto the rear of thecarapace and the turtles were returned to theircapture location within one hour To estimatebody temperature during winter a small tem-perature data logger (6 05uC iButton Maxim-Dallas Semiconductor Sunnyvale CA) wasepoxied to the carapace adjacent to the trans-mitter (four turtles outfitted on 23 October 2004one on 29 October 2004) Many studies havefound that turtle body temperatures in generalare highly related to environmental tempera-tures (Ernst 1982 1986 Peterson 1987 Ernst etal 1989) and Wood Turtles are described astemperature conformers (Ernst 1986) Thus weassumed that data logger temperatures repre-sented accurate measurements of body tem-peratures especially because turtles were inwater during winter

Tracking of radio-tagged turtles was carriedout on foot using a Telonics (Mesa AZ) receiverand a three-element Yagi antenna (WildlifeMaterials Inc Murphysboro IL) From Novem-ber 2004 through March 2005 four turtles wereradio-located 14 times and one turtle was radio-located 13 times The study site was visited twoto three times per week from October throughNovember 2004 at which time turtle activitywas relatively high For each fall radio locationwe recorded air and water temperaturesriverbed substrate (eg sand cobble leaf litter)as well as turtle behavior and movements sincelast sighting From December 2004 to March2005 at which time turtle activity was relativelylow the study site was visited every seven to12 days The site was accessed using crosscountry skis and snow shoes therefore thefrequency of site visits depended on severity ofwinter weather For each winter radio locationwe recorded distance moved since last trackingair and water temperatures and physicalchanges to the river as well as turtle behaviorAfter the river surface became covered with icethe behavior of turtles could not be observed

Turtle movements were recorded in winter byresearchers who stood on the ice surface aboveeach turtle When a turtle was located a circlewas spray-painted onto the ice above the turtlewith the size of the circle (20ndash40 cm diameter)depending on the area where the strongestsignal was perceived At the next radio-trackingdate the distances between the edges of thecircles and centers of the circles were recordedusing a 60-m fiberglass measuring tape Home-range size was estimated using the center pointsof each circle and movements were measuredusing the edges of the circles to incorporateerror from radio-tracking We also recorded theangle at which the turtle moved from theprevious location Winter home-range size was

then estimated using the minimum convexpolygon (MCP) method by mapping center-to-center measurements on graph paper Distancefrom shore for each turtle was measured usingthe shoreline or the edge of the ice as the zeropoint On 5 February 2005 holes were drilledthrough the ice using an auger at two locationsin an attempt to visualize overwintering turtlesone turtle was observed

Temperature stations were established alongthe river Two air temperature stations werepositioned in areas used by the study animalsduring fall Air temperature stations recordedambient environmental temperature fluctua-tions along the river Four water temperaturestations were placed in areas where turtles withtransmitters had been located for week-longperiods in late fall We had assumed these areaswould be used for overwintering because theyresembled hibernacula described in the litera-ture (eg Ernst 1986 Ernst et al 1994) Wedeployed two types of water temperaturestations (1) bricks (N 5 2) to which data loggerswere epoxied at turtle carapace height (8 cm)thus serving as rough models of Wood Turtlebody temperature in water and (2) cinderblocks (N 5 2) to which data loggers wereepoxied at various distances from the basesediment temperature (0 cm from base) turtlecarapace height temperature (8 cm) and watercolumn temperature (30 cm) Data loggers werelaunched to synchronously and continuouslyrecord temperatures at 3-h intervals for theduration of winter We compared estimatedturtle body temperatures to air and watertemperatures to examine temperature profilesduring winter temperature selection and ther-mal triggers for certain behaviors (eg entranceintoexit from hibernation movements duringwinter)

Statistical AnalysesmdashAll analyses were con-ducted using Statistica 60 (StatSoft Tulsa OK)Differences between males and females indistance from shore and home-range size weretested using Mann Whitney U-tests (lack ofnormality was confirmed using K-S tests)Temperature data for the winter (1 Decemberthrough 30 March) were divided into 10-dayperiods (N 5 80 temperature records in eachperiod) which ensured equal sample sizes forthe statistical analyses Differences in air andwater temperatures among stations and fromturtle body temperatures were tested usingrepeated measures ANOVAs on the means forthe 10-day periods Duncanrsquos multiple rangetests were used for post hoc analyses A Pearsoncorrelation analysis was used to test for a re-lationship between variation in body tempera-ture and distance moved between tracking

34 W F GREAVES AND J D LITZGUS

dates to determine whether movements wererelated to changes in body temperature

RESULTS

HibernaculamdashWe identified five areas whereWood Turtles overwintered at the study siteeach area was occupied by a single Wood Turtleoutfitted with a transmitter All hibernaculawere within the river on sandy substrate ata mean distance of 10 m from shore (Fig 1)and in relatively shallow water (1 m deep)There was no significant difference betweenmales and females with respect to distance fromshore (U 5 7 N 5 5 P 010) No hibernaculawere located in the readily available roothollows oxbows beaver lodges muskrat holesor within hollowed-out areas of the riverbank

Three turtles overwintered exposed on theriverbed without the use of a protective struc-ture or cover The other two turtles also over-wintered on the riverbed however they werewithin close proximity to a log or resting onleaf litter that could have been used for coverOne of the latter two turtles used a deep pool( 15 m water depth) however the rest didnot There was no evidence of communaloverwintering Two turtles that were engagedin mating behavior from 5 October until 6November separated and overwintered approx-imately 15 m apart The ice-cover period wasapproximately 116 days (9 December to 4April) although ice had formed and thawedon the river as well as on adjacent water bodies(eg tributaries oxbows beaver ponds) before27 November The river was completely frozenover by 15 December

TemperaturemdashAir and water temperaturesgradually decreased throughout fall (Table 1)The last known turtle basking date was 30October when the air temperature was 85uCand water temperature was 50uC Two turtleswere observed mating on 6 November at a watertemperature of 50uC After this date watertemperatures and movements decreased andremained low for the rest of the winter Watertemperatures dropped to 05uC by 11 Novem-ber however an unseasonable warm spelloccurred during November and no ice formedon the river until approximately 9 DecemberWater temperatures during the month of Octo-ber and November averaged 74uC and 25uCrespectively from December through Marchwater temperatures averaged 206uC (Table 1)Temperatures at different water depths (0 cm8 cm 30 cm) showed little variation (6 05uCTable 1) and these variations were not largerthan the error of the data loggers (6 05uC) Thefirst emergence was on 16 April at an air

FIG 1 Box plot of mean (horizontal line) standarderror (box) 95 confidence interval (vertical line) andextreme points (squares) distance from shore (m)recorded from center of the strongest telemetry signalto water or ice edge for five radio-tagged WoodTurtles (Glyptemys insculpta) in the Sudbury DistrictOntario from 9 November 2004 to 19 March 2005N 5 14 radiolocations for each turtle

TABLE 1 Mean 6 SE (N) monthly temperatures (uC) recorded by data loggers (iButtons) from 24 October 2004to 30 March 2005 at a Wood Turtle (Glyptemys insculpta) site in the Sudbury District Ontario lsquolsquo0 cm 8 cm and30 cmrsquorsquo represent water column temperatures at the stated heights from the riverbed substrate lsquolsquoTurtlersquorsquorepresents the mean estimated body temperature of N 5 5 radio-tagged Wood Turtles lsquolsquo0 cm 30 cmrsquorsquo andlsquolsquoAirrsquorsquo each represent the means of N 5 2 temperature stations lsquolsquo8 cmrsquorsquo represents the mean of N 5 4temperature stations (two bricks and two cinder blocks see Materials and Methods for details) Sample sizesvary in October because two data loggers were launched five days after the others Note that the statisticalanalyses comparing among temperature stations were conducted using repeated-measures ANOVAs on meansgenerated for 10-day periods for winter only (1 December through 30 March) thus values and sample sizesdiffer between Table 1 and the statistical results in the text

Station October November December January February March

0 cm 74 6 01 (128) 24 6 01 (480) 205 6 00 (496) 205 6 00 (496) 205 6 00 (448) 206 6 00 (480)8 cm 74 6 01 (256) 25 6 01 (960) 206 6 00 (992) 206 6 00 (992) 206 6 00 (896) 207 6 00 (960)30 cm 74 6 01 (128) 25 6 01 (480) 205 6 00 (496) 205 6 00 (496) 207 6 00 (448) 208 6 00 (480)Air 62 6 04 (83) 208 6 02 (480) 2106 6 04 (496) 2150 6 04 (496) 287 6 04 (448) 260 6 04 (480)Turtle 77 6 01 (274) 26 6 01 (1200) 204 6 00 (1240) 205 6 00 (1240) 205 6 00 (1120) 205 6 00 (1200)


temperature of 135uC and a water temperatureof 45uC Average water temperature at firstemergence was 50uC and varied from 45ndash55uCAll turtles emerged from hibernation by 19April

Temperature records from data loggers al-lowed us to compare among and betweenenvironmental and turtle body temperaturesThe mean body temperature of the five over-wintering turtles was 205uC 6 0004 (range210 to 10uC N 5 4800 for all five turtlescombined) from 1 December to 30 MarchDuring the same period air temperaturesfluctuated substantially reaching a maximumof 105uC (30 March 2005) and reaching theminimum temperature recording limit of thedata logger 2400uC (21 January 2005) averageair temperature was 283uC The grand modelcomparing temperatures among all turtles andall stations during winter (1 December through30 March) indicated significant differencesamong temperatures (F12168 5 255 P laquo00001) There were significant differencesamong turtle body temperatures during thiswinter period (F624 5 1694 P laquo 00001) Twoturtles had significantly different mean bodytemperatures from each other (210uC and00uC respectively) and from the other threeturtles (205uC) (Duncanrsquos post hoc test P 00001) However because the accuracy of thedata loggers was 6 05uC the statistical signif-icance may not be biologically meaningfulbecause the variation between individual turtlebody temperatures is within the degree of errorof the data loggers

We compared turtle body temperatures to airtemperatures and to the 8 cm water tempera-tures (a rough turtle model) to examine thedegree of thermal buffering provided by theriver Turtle body temperatures and air tem-peratures differed from each other throughoutthe winter (F1272 5 285 P laquo 00001) turtle bodytemperatures were always significantly warmerthan air temperatures (Duncanrsquos post hoc test P 00001 in all cases) Turtle body temperaturegenerally decreased from October to Novemberbut then remained low and unchanged fromDecember through March (Table 1) Althoughthe water temperature at one 8-cm station(turtle model) was significantly different fromall other water temperature stations (F963 5380 P laquo 00001 Duncanrsquos post hoc test P 00001) there were no significant differencesamong the other 30- 8- or 0-cm stations(Duncanrsquos post hoc tests P 005 in all cases)Four of five turtlesrsquo body temperatures differedfrom the 8-cm water temperature station notedabove (F1188 5 388 P laquo 00001 Duncanrsquos posthoc test P 00001) however no other 8-cmstations differed from turtle body temperatures

(Duncans post hoc test P 005 in pairwisecomparisons of individual turtles and 8-cmstations)

ActivitymdashTurtles made small movementsduring winter One individual moved 10 mbetween radio locations (Fig 2) when the watertemperature was 205uC There was no correla-tion between changes in body temperature anddistance moved between radiolocations (r 5

20068 N 5 69 P 5 076 y 5 117 2 080x) from9 November to 19 March Many of the wintermovements were parallel to the shoreline of theriver and most were upstream in directionOnly 8 of the movements between radioloca-tions were 5 m and movements 1 mcomprised 41 of the total observations 7 ofthe movements were between 30 m and 49 mand 44 were between 10 m and 29 m Winterhome-range size averaged 71 m2 (6 15 SE) forthe five Wood Turtles outfitted with transmit-ters There was no significant difference be-tween male and female home-range sizes (U 51 N 5 5 P 5 010) All five turtles withtransmitters successfully emerged after winter

DISCUSSION

Hibernacula and BehaviormdashIn the SudburyDistrict Wood Turtles overwintered aquaticallyin a sand-bottom slow-moving meanderingriver that was completely frozen over by 15December Wood Turtles remained in relativelyexposed areas on the river bottom throughoutthe winter period Thus Wood Turtles in ourstudy did not appear to use sites that wouldoffer protection against predation We obtainedpictures and video of one female overwintering

FIG 2 Box plot of mean (horizontal line) standarderror (box) 95 confidence interval (vertical line) andextreme points (squares) distance moved betweenradiolocations for five radio-tagged Wood Turtles(Glyptemys insculpta) in the Sudbury District Ontariofrom 9 November 2004 to 19 March 2005 N 5 14radiolocations for each turtle


under the ice The female was resting exposedon the river bottom with her marginals un-covered After the hole was drilled through theice she extended her head and limbs from hershell and moved approximately 5 cm awayfrom the light and then retreated back insideher shell Similarly Graham and Forsberg(1991) observed turtles overwintering adjacentto structures such as logs or rocks but not usingthem for protection In other studies to thesouth hibernacula used by Wood Turtles wereusually deep pools under overhanging roots orlog jams in a stream beaver lodges or muskratburrows (Ernst et al 1994) Other studies inCanada have noted hibernacula that were in theriver bank or in a sand bottom river but give nofurther details (Foscarini 1994 Arvisais et al2004) Without cover turtles make themselvesvulnerable to visual predators such as riverotters (Lutra canadensis) Otter tracks and slidesand entrance holes under the ice were observedat our study site Although ice-cover may act asa sufficient barrier to predation during hiber-nation (Taylor and Nol 1989) river otters canstill depredate overwintering turtles (Brooks etal 1991) It is likely that before and after ice-cover turtles are most vulnerable to predationTurtles may be vulnerable before ice-coverwhen they are lethargic because of low watertemperatures Turtles can also be lethargic andvulnerable to predation upon emergence fromoverwintering because of prolonged hypoxiaand metabolic acidosis (Sexton 1959 Wilbur1975 Litzgus et al 1999 Ultsch 2006) Turtlesin our study used concealed areas in Septemberand October however by November (before ice-cover) turtles had moved away from theseprotective sites nonetheless we found nowinter mortality from predation

Wood Turtles in the Sudbury District did notoverwinter communally as previously docu-mented in southern populations of the species(Bloomer 1978) Movements during winter didnot appear to be directed toward other WoodTurtles In fact a male and female engaged inmating behavior on 6 November 2005 gradual-ly moved away from one another throughoutthe winter In light of the Wood Turtlersquoshierarchical social structure (Kaufmann 1992)it has been hypothesized that Wood Turtleshibernate communally as a result of socialinteractions and not because optimal hibernac-ula are limited (Bloomer 1978) The degree ofcommunal hibernation may also be related topopulation density such that in denser popula-tions there is a greater tendency towardcommunal overwintering simply as a result ofa greater number of individuals at the site Lackof suitable hibernacula at the northern extremeof a speciesrsquo range may result in communal

overwintering (Gregory 1982) however com-munal overwintering was not seen at ournorthern site Communal overwintering mayalso occur to facilitate mating by increasingopportunities to find mates or improve fitnessby synchronizing emergence (Gregory 1982Ultsch 1989) Mating attempts between twoindividuals were observed before ice-cover (6November) however no other turtles were seenmating in the areas used for overwintering It ismore probable that the return of females to theriver in the fall and slow movement of femalesaway from the river prior to nesting providemore opportunities for mating than would beavailable in communal hibernacula Additionalwinter studies with larger sample sizes areneeded to examine whether communal over-wintering occurs at the northern extreme of theWood Turtlersquos range

Wood Turtles overwintered at a mean riverdepth of 1 m and a mean distance of 10 mfrom shore By remaining 10 m from shoreturtles may ensure they remain away from thestrong current in the middle of the river and arenot subsequently swept away and accidentallyrelocated If hibernacula are a limiting factor innorthern populations accidental relocations inmidwinter from an area used for overwinteringmay be hazardous By remaining in a depth of1 m Wood Turtles are protected from surfaceice Ice thickness particularly in areas close toshore was observed to be over 50 cm exposureto ice during winter would most likely causedeath (Storey and Storey 1989) Riverine hiber-nacula may increase the chance of turtlemortality from freezing because of fluctuatingwater levels which may leave the turtleexposed to ice or air (Brown and Brooks1994) At our study site water levels fluctuatedduring rare rain occurrences in late Decemberand early February as well as after the onset ofice however no Wood Turtle mortality wasobserved Overwintering turtles may be re-stricted to water that is deep enough to avoiddanger from overhead ice but in areas closeenough to shore to be away from strongcurrents that could carry them downstream

TemperaturemdashAquatic hibernacula providea buffered thermal refuge from fluctuating airtemperatures during the long cold northernwinters Air temperatures at our site reachedbelow 2400uC whereas water temperaturesremained near 0uC during ice-cover Similarlywater temperatures near 0uC have been re-corded in other winter ecology studies of turtles(eg Crawford 1991 Brown and Brooks 1994)Most laboratory studies related to turtle over-wintering have used temperatures of 30uC (egUltsch and Jackson 1982 1985 Ultsch andCochran 1994) because stratification in ponds


tends to keep temperatures warmer than thefreezing point of water However small riversand streams do not stratify and typically remainuniform in temperature because of mixing(Allan 1995) The entire water column of a riverwill approach 0uC before ice begins to form(Sheridan 1961) Thus by using a riverinehabitat Wood Turtles may have to overwinterin colder environments for longer periods oftime than other chelonians that use ponds suchas Snapping Turtles (Chelydra serpentina Ultsch1983 Brown and Brooks 1994) and PaintedTurtles (Chrysemys picta Peterson 1987 Taylorand Nol 1989 St Clair and Gregory 1990) Theability of Wood Turtles in northern environ-ments to choose sites with low environmentaltemperatures during winter may be advanta-geous Given that turtles are ectotherms expo-sure to temperatures close to 0uC should reducemetabolic rates thereby conserving energywhich may be especially important at northernlatitudes where turtles are subjected to extreme-ly long dormancy periods without access tofood (Gregory 1982) Perhaps Wood Turtles inthe far north can not afford to overwinter attemperatures above 0uC because they will burnup their energy reserves before winter endsthus northern turtles must use cooler hibernac-ula than their southern conspecifics In additionreptiles in northern latitudes generally havelower critical minimum temperatures thansouthern reptiles this is presumably an adap-tation to endure low temperatures duringwinter and cold episodes during the activityperiod (Saint Girons and Saint Girons 1956)Alternatively Wood Turtles at our site mayoverwinter in colder habitats simply becausethe environment is colder relative to moresouthern latitudes

During winter Wood Turtles did not appearto select specific water temperatures Ourcomparison of estimated turtle body tempera-tures with turtle model temperatures (dataloggers at 8 cm from river substrate) generallyshowed no differences We had only four 8-cmdata loggers (two on bricks two on cinderblocks) deployed in the river future work willinclude multiple data loggers in the river so thatvarious depths and substrates are monitored inan effort to determine whether Wood Turtlesare selecting or avoiding certain temperaturesduring hibernation

The specific environmental cues stimulatingentrance into or exit from hibernation in turtlesremain unknown (Crawford 1991) Circannualrhythms are most likely not the stimulusbecause emergence and entrance times aresubject to weather which is highly variable(Ultsch 1989) We documented mating andbasking behaviors until water temperatures

dropped below 5uC Basking was not witnessedagain until spring when water temperaturesreached between 4uC and 5uC Thus WoodTurtles may have a thermal trigger for entranceinto and exit from hibernation between 4uC and5uC If temperature is not the stimulus foremergence other possibilities may be thesudden increase in dissolved oxygen after ice-off photostimulation or rising water levels(Crawford 1991 Allan 1995) In March turtlesshowed an increase in movements perhapschanging ice conditions and increased dissolvedoxygen were the causes

ActivitymdashActivity patterns of Wood Turtleslike those of other ectotherms are generallyhighly influenced by environmental tempera-tures Surprisingly we found that in winterturtles moved and that this activity was notrelated to temperature as water temperaturesvaried little throughout the winter and therelationship between distance moved andchange in body temperature was not significantMost previous studies ceased radio-tracking inthe fall reported that turtles had minimalmovements or that turtles were inactive fromNovember to May (eg Foscarini 1994 Arvisaiset al 2002) Ours was not the first study to findthat turtles moved during winter this phenom-enon has also been documented in studies ofother turtle species at more southern locales (egCarr 1952 Sexton 1959 Gibbons 1968 Conant1975 Taylor and Nol 1989) Because mostmovements were parallel to the shoreline winterhome ranges for our Wood Turtles were longand narrow and winter home-range size wasabout 7 m2 Similarly in Massachusetts eachhibernating Wood Turtle remained in an area of6ndash8 m2 (Graham and Forsberg 1991) Interest-ingly the turtle (a male) in our study thatoverwintered with the warmest body tempera-ture (mean 5 00uC from 2 December to 3 April)had the smallest home-range size (21 m2)

ConclusionsmdashOur hypotheses were not fullysupported Although Wood Turtles used aquat-ic sites for overwintering which provideda buffered thermal environment and preventedexposure to lethal freezing temperatures theydid not use sites with cover or structure toprotect from predation In addition WoodTurtles were active during winter and did notoverwinter communally even though suitablehibernacula may be a limiting resource at ournorthern site Future work will include a largersample size and will try to quantify specificvariables that Wood Turtles may select foroverwintering such as dissolved oxygen tem-perature substrate type depth and physicalstructure Our winter research provides newdata that will help identify critical habitats thatare important for overwintering as well as help


to locate new populations in northern habitatsthat meet the speciesrsquo specific overwinteringrequirements

AcknowledgmentsmdashFinancial support for thisresearch came from NSERC Laurentian Uni-versity and the Ontario Ministry of NaturalResources Species at Risk Fund WFG wassupported by scholarships and bursaries fromthe Niagara Conservation Authority HBPAand the CIBC Wood GundyFranklin G TPickard Memorial fund while conducting thisresearch for his Honours Thesis at LaurentianUniversity The study was conducted under theguidelines of the Canadian Council on AnimalCare and the Laurentian University AnimalCare Committee (protocol 2004-09-01) T Mer-ritt provided comments on an earlier draft ofthe manuscript We would like to thank variouspeople for help with field data collection BBeaton J Dick J Enneson M Hall J Hamr LKeable T Merritt D Reeves L Vine andespecially J Beaton who helped collect dataeven on the 240uC days

LITERATURE CITED

ALLAN J D 1995 Stream Ecology Structure andFunction of Running Waters Chapman and HallLondon

ARVISAIS M J C BOURGEOIS E LEVESQUE C DAIGLE DMASSE AND J JUTRAS 2002 Home range andmovements of a Wood Turtle (Clemmys insculpta)population at the northern limit of its rangeCanadian Journal of Zoology 80402ndash408

ARVISAIS M E LEVESQUE J C BOURGEOIS C DAIGLE DMASSE AND J JUTRAS 2004 Habitat selection by theWood Turtle (Clemmys insculpta) at the northernlimit of its range Canadian Journal of Zoology82391ndash398

BLOOMER T J 1978 Hibernacula congregating in theClemmys genus Journal of the Northern OhioAssociation of Herpetologists 437ndash42

BROOKS R J G P BROWN AND D A GALBRAITH 1991Effects of a sudden increase in natural mortality ofadults on a population of the common SnappingTurtle (Chelydra serpentina) Canadian Journal ofZoology 691314ndash1320

BROWN G P AND R J BROOKS 1994 Characteristics ofand fidelity to hibernacula in a northern popula-tion of Snapping Turtles Chelydra serpentinaCopeia 1994222ndash226

CARR A F 1952 Handbook of Turtles CornellUniversity Press Ithaca NY

CLOUDSLEY-THOMPSON J L 1971 The Temperature andWater Relations of Reptiles Merrow PublishingCo Ltd Watford Herts UK

CONANT R 1975 A Field Guide to the Reptiles andAmphibians of Eastern and Central North Amer-ica 2nd ed Houghton and Mifflin Boston MA

CRAWFORD K M 1991 The winter environments ofPainted Turtles Chrysemys picta temperaturedissolved oxygen and potential cues for emer-gence Canadian Journal of Zoology 692493ndash2498

ERNST C H 1982 Environmental temperatures andactivities in wild Spotted Turtles Clemmys guttataJournal of Herpetology 16112ndash120

mdashmdashmdash 1986 Environmental temperatures and activ-ities in the Wood Turtle Clemmys insculpta Journalof Herpetology 20222ndash229

ERNST C H J E ZAPPALORTI AND J E LOVICH 1989Overwintering sites and thermal relations ofhibernating Bog Turtles Clemmys muhlenbergiiCopeia 1989761ndash764

ERNST C H J E LOVICH AND R W BARBOUR 1994Turtles of the United States and Canada Smithso-nian Institution Press Washington DC

FOSCARINI D A 1994 Demography of the Wood Turtle(Clemmys insculpta) and Habitat Selection in theMaitland River Valley Unpubl masterrsquos thesisUniversity of Guelph Guelph Ontario Canada

GIBBONS J W 1968 Reproductive potential activityand cycles in the Painted Rurtle Chrysemys pictaEcology 49399ndash409

GRAHAM T E AND J E FORSBERG 1991 Aquaticoxygen uptake by naturally wintering WoodTurtles Clemmys insculpta Copeia 1991836ndash838

GREGORY P T 1982 Reptilian hibernation In C Gansand F H Pough (eds) Biology of the ReptiliaVol 13 Physiology D pp 53ndash154 Academic PressLondon

HARDING J H AND T J BLOOMER 1979 The WoodTurtle Clemmys insculpta hellip a natural historyBulletin of New York Herpetological Society 159ndash26

KAUFMANN J H 1992 The social behavior of WoodTurtles Clemmys insculpta in central PennsylvaniaHerpetologcal Monographs 61ndash25

KLEMENS M W 2000 Turtle Conservation Smithso-nian Institution Press Washington DC

LITZGUS J D AND R J BROOKS 1996 Status of theWood Turtle Clemmys insculpta in CanadaCommittee of the Status of Endangered Wildlifein Canada (COSEWIC) Canadian Wildlife ServiceOttawa Ontario Canada

LITZGUS J D J P COSTANZO R J BROOKS AND R E LEE1999 Phenology and ecology of hibernation inSpotted Turtles (Clemmys guttata) near the north-ern limit of their range Canadian Journal ofZoology 771348ndash1357

PETERSON C C 1987 Thermal relations of hibernatingPainted Turtles Chrysemy picta Journal of Herpe-tology 2116ndash20

SAINT GIRONS H AND M C SAINT GIRONS 1956 Cycledrsquoactivite et thermoregulation chez les reptiles(lezards et serpents) Vie Milieu 7133ndash226

SEXTON O J 1959 Spatial and temporal movements ofa population of the Painted Turtle Chrysemys-picta-marginata (Agassiz) Ecological Monographs29113ndash140

SHERIDAN W L 1961 Temperature relationships ina pink salmon stream in Alaska Ecology 4291ndash98

ST CLAIR R C AND P T GREGORY 1990 Factorsaffecting the northern range limit of PaintedTurtles (Chrysemys picta) winter acidosis or freez-ing Copeia 19901085ndash1089

STOREY K B AND J M STOREY 1989 Freeze toleranceand freeze avoidance in ectotherms In L C Wang(ed) Advances in Comparative and Environmen-tal Physiology Vol 4 pp 51ndash82 Springer-VerlagBerlin Germany


TAYLOR G M AND E NOL 1989 Movements andhibernation sites of overwintering Painted Turtlesin southern Ontario Canadian Journal of Zoology671877ndash1881

ULTSCH G R 1983 Radiotelemetric observations ofwintering Snapping Turtles (Chelydra serpentina) inRhode Island Journal of the Alabama Academy ofScience 54200ndash206

mdashmdashmdash 1985 The viability of nearctic freshwaterturtles submerged in anoxia and normoxia at 3and 10uC Comparative Biochemistry and Physiol-ogy 130331ndash340

mdashmdashmdash 1989 Ecology and physiology of hibernationand overwintering among fresh-water fishesturtles and snakes Biological Reviews of theCambridge Philosophical Society 64435ndash1989

mdashmdashmdash 2006 The ecology of overwintering amongturtles where turtles overwinter and its conse-quences Biological Reviews 81339ndash367

ULTSCH G R AND B M COCHRAN 1994 Physiology ofnorthern and Southern Musk Turtles (Sternotherusodoratus) during simulated hibernation Physiolog-ical Zoology 67263ndash281

ULTSCH G R AND D C JACKSON 1982 Long-termsubmergence at 3uC of the turtle Chrysemys pictabellii in normoxic and severely hypoxic water ISurvival gas exchange and acid-base statusJournal of Experimental Biology 9611ndash28

mdashmdashmdash 1985 Acid-base status and ion balance duringstimulated hibernation in freshwater turtles fromthe northern portions of their ranges Journal ofExperimental Zoology 273482ndash493

WILBUR H M 1975 The evolutionary and mathemat-ical demography of the turtle Chysemys pictaEcology 5664ndash77

Accepted 17 September 2006


Overwintering Ecology of Wood Turtles (Glyptemys insculpta) at theSpeciesrsquo Northern Range Limit

WILLIAM F GREAVES AND JACQUELINE D LITZGUS1

Department of Biology Laurentian University Sudbury Ontario P3E 2C6 Canada

ABSTRACTmdashSeasonal variation in activity patterns of reptiles is accompanied by physiological and

behavioral adjustments that influence their ecology and life history and overwinter survival may be an

important factor limiting a speciesrsquo northern range extension A northern population of Wood Turtles

(Glyptemys insculpta) in Ontario Canada was surveyed in fall 2004 and a subset of adults was radio-tracked

every 7ndash12 days during the winter of 2004ndash2005 to examine thermal aspects of overwintering We predicted

that Wood Turtles would use hibernacula that protect them from freezing and predation Temperature data

loggers indicated that turtle body temperatures and hibernacula temperatures remained near 0uC from 2

December 2004 until 3 April 2005 During the same period air temperatures fluctuated substantially and

reached a maximum of 105uC (on 30 March 2005) and a minimum of less than 240uC (on 21 January 2005)

with a mean of 283uC Turtles did not select specific water temperatures nor did they use distinct structures

(eg root hollows logjams and holes in the riverbank) for overwintering but instead rested relatively

exposed on the riverbed at a depth of approximately 1 m and at a mean distance of 10 m from the riverbank

Surprisingly turtles made small movements during winter (01ndash100 m between radiolocations) typically

against the river current and in a direction parallel to the riverbank Average winter home-range size was

71 m2 Our findings raise questions about why turtles move during winter we suggest possible answers and

future lines of investigation to address these questions

Seasonal variation in activity patterns ofreptiles requires physiological and behavioraladjustments that influence both their ecologyand life history (Crawford 1991) This isespecially true for reptiles at northern latitudeswhere winter imposes harsh and unfavourableconditions for extended periods of time (StClair and Gregory 1990) The unpredictableconditions associated with seasonality at north-ern latitudes contribute to the observed de-crease in species diversity with increasinglatitude (Cloudsley-Thompson 1971) Mostreptiles tolerate cold winter temperatures andavoid mortality from freezing by overwinteringin thermally stable refugia (Gregory 1982Ultsch 1989) Aquatic turtles typically utilizesome form of aquatic medium as their thermalrefuge in winter (Brown and Brooks 1994Ultsch 2006) however temperatures withinhibernacula in northern climates can still ap-proach 0uC Because of decreased mobility fromlow temperatures turtles are at risk of mortalityfrom the inability to flee dangerous circum-stances such as predators or exposure toextreme temperatures from fluctuating waterlevels during overwintering (Brooks et al1991) Therefore the thermal suitability ofa turtle to its hibernaculum may be the most

important factor affecting the speciesrsquo over-wintering success (Gregory 1982) Thus turtlesmust use hibernacula with characteristics thatwill promote overwinter survival (Ultsch 19852006) including protection from predators andfreezing temperatures (Brown and Brooks1994)

Although the winter ecology of Wood Turtles(Glyptemys insculpta) has been described insouthern populations (eg Ernst 1986 Grahamand Forsberg 1991) there are no published dataon the overwintering ecology at the northernextreme of the speciesrsquo range Previous studieshave found that Wood Turtles in southernlocales overwinter in slow-moving streams thatdo not freeze over (Ernst et al 1994) Depend-ing on geographical region Wood Turtles beginoverwintering between late October and thefirst week of November (Harding and Bloomer1979 Ernst et al 1994) At the most northernlatitude studied to date (Quebec Canada46u389N) most turtles entered hibernation bythe first week of November (Arvisais et al2002) Hibernacula in more southern localesinclude deep pools under overhanging roots orlogs along a river muskrat burrows and inbeaver ponds (Ernst 1986) Generally WoodTurtles prefer streams with relatively highoxygen concentrations that do not freeze (Gra-ham and Forsberg 1991 Ernst et al 1994)which decreases the need for anaerobic activityduring overwintering (Ultsch and Jackson 19821 Corresponding Author E-mail jlitzguslaurentianca

Journal of Herpetology Vol 41 No 1 pp 32ndash40 2007Copyright 2007 Society for the Study of Amphibians and Reptiles


















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Documents

Overwintering Ecology of Wood Turtles (Glyptemys Insculpta) at the Species' Northern Range Limit