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ORIGINAL ARTICLE
Diurnal variation in the behaviour of the Pink-footed Goose(Anser brachyrhynchus) during the spring stopoverin Trøndelag, Norway
Magda Chudzinska • Jesper Madsen •
Jacob Nabe-Nielsen
Received: 19 June 2012 / Revised: 1 December 2012 / Accepted: 19 December 2012 / Published online: 10 January 2013
� Dt. Ornithologen-Gesellschaft e.V. 2013
Abstract During the spring migration, the Pink-footed
Goose Anser brachyrhynchus stops in mid-Norway to refuel
before continuing its flight to the Svalbard breeding grounds.
While in mid-Norway the geese feed on pasture, stubble
and newly sown grain fields. Here, we describe the diurnal
variation in goose behaviour at a staging site and assess the
extent to which behavioural patterns are attributable to
physiological factors (digestibility of the food) and environ-
mental conditions (flock size, type and frequency of distur-
bance and distance to roost). We found that feeding activity
peaked at mid-day, whereas the birds were most alert in the
morning and afternoon. The behaviour of Pink-footed Goose
also varied with habitat type, disturbance level and distance to
roost. The diurnal variation in feeding activity differed from
behaviour reported for geese on the wintering grounds, indi-
cating that the birds have different energetic and nutrient
demands when at spring staging sites. Seasonal changes in
habitat availability as well as density dependence may also
affect the birds’ behavioural patterns. A sporadic, unpredict-
able disturbance reduced the proportion of geese feeding to a
greater extent than a predictable, recurrent disturbance, but
feeding activity was highest under undisturbed conditions.
Keywords Activity patterns � Disturbance �Foraging behaviour � Stopover site
Zusammenfassung
Veranderungen im Verhalten von Kurzschnabelgansen
(Anser brachyrhynchus) im Tagesverlauf wahrend ihrer
Fruhlingsrast in Trøndelag, Norwegen
Wahrend des Fruhjahrszuges rasten Kurzschnabelganse
in Mittelnorwegen, um vor ihrem Weiterflug in die
Brutgebiete in Spitzbergen nochmals Nahrung aufzuneh-
men. In Mittelnorwegen fressen diese Ganse auf Wei-
deland, Stoppelfeldern und frischer Getreidesaat. Diese
Untersuchung beschreibt die tageszeitlichen Veranderun-
gen im Verhalten der Ganse an einem Rastplatz und
beurteilt, inwieweit Verhaltensmuster mit physiologischen
Faktoren (Verdaubarkeit des Futters) und Umweltbe-
dingungen (Gruppengroße, Art und Haufigkeit von Storun-
gen und Entfernung vom Schlafplatz) in Verbindung
gebracht werden konnen. Die Futteraufnahme hatte ihren
Hohepunkt um Mittag, wahrend die Vogel am Morgen
und Nachmittag am wachsamsten waren. Das Verhalten
der Kurzschnabelganse unterschied sich auch in Abhan-
gigkeit von Habitat, Ausmaß von Storungen und der
Entfernung vom Schlafplatz. Die tageszeitlichen Veran-
derungen in der Nahrungsaufnahme unterschieden sich
von denen, die uber Ganse im Winterquartier berichtet
wurden, was darauf hindeutet, dass die Vogel wahrend
ihrer Fruhjahrsrast unterschiedliche energetische und
Nahrstoff-Anforderungen haben. Auch saisonale Veran-
derungen in der Habitatverfugbarkeit und Dich-
teabhangigkeit konnten die Verhaltensmuster der Vogel
beeinflussen. Sporadische, unvorhersehbare Storungen
verringerten den Anteil an fressenden Gansen in starke-
rem Maße als vorhersagbare, wiederkehrende Storungen,
aber die Fraßaktivitat war am hochsten unter ungestorten
Bedingungen.
Communicated by F. Bairlein.
M. Chudzinska (&) � J. Nabe-Nielsen
Department of Bioscience, Aarhus University,
Frederiksborgvej 399, 4000 Roskilde, Denmark
e-mail: [email protected]
J. Madsen
Department of Bioscience, Arctic Research Centre,
Aarhus University, C.F. Møllers Alle 8, 8000 Aarhus, Denmark
123
J Ornithol (2013) 154:645–654
DOI 10.1007/s10336-012-0927-y
Introduction
Migratory birds are expected to optimise their foraging
behaviour at spring staging sites and their timing of arrival
at the breeding grounds in order to maximise reproductive
output (Alerstam and Lindstrom 1990; Prop et al. 2003).
For birds migrating in steps, stopover sites allow for
refuelling and should provide sufficient food during the
birds’ stay (Bauer et al. 2006). The optimal conditions for
the birds are limited in time and space, and migration
phenology is therefore governed by a chain of individual
decisions, such as when to arrive at and leave a stopover
site (Duriez et al. 2009) and when and how intensively to
forage. Such decision-making suggests that during stop-
overs birds have to adapt their behaviour to maximize
energy and nutrient intake while minimizing energy
expenditure and predation risk such that food can be
ingested and processed at maximum capacity (Hedenstrom
2008).
Energy intake rates in wild animals are limited by the
rate at which food can be processed in the digestive tract
(Kvist and Lindstrom 2000). The quality of the consumed
food may therefore influence animal behaviour. For her-
bivores, the amount of energy extracted from the food
depends on the nature of the digestible component and by
the digestion rate while the food is in the alimentary tract
(Demment and Soest 1985). In order to maximise their
energy intake rate, herbivores must select high-quality
plant parts containing easily metabolisable materials, such
as proteins and soluble carbohydrates (Karasov 1990).
However, in order to meet both energetic and nutritional
demands, geese must also feed on lower energy food types.
Such foods usually contain more cellulose or hemicellu-
lose, both of which require longer retention times in the gut
to be digested. A prolonged retention time has a cost, since
it is inversely proportional to the amount of food that can
be processed per unit time (Prop and Vulink 1992). In order
to increase the retention time and gain more energy, geese
feeding on low-energy food are forced to interrupt feeding
with rest periods to allow the ingested food to pass through
the alimentary tract (Prop and Vulink 1992; Owen 1972).
Due to physiological constraints, the diurnal feeding
activity of geese may therefore vary with the food source as
a result of differences in the digestion rate (Kvist and
Lindstrom 2000; Therkildsen and Madsen 2000a). In
Trøndelag, mid-Norway, the migratory Pink-footed Goose
feeds on both pasture, stubble and newly sown barley grain
(Madsen et al. 1997). Barley grain is digested twice as fast
as grass because of its lower cellulose content (Madsen
1985). Geese feeding on grain can therefore increase their
daily net energy intake more easily than those feeding
exclusively on pasture (Madsen 1985). Although grain is
more energy rich than grass, it contains fewer of the amino
acids essential for building muscles and for egg production
(McDonald et al. 1973), so geese in mid-Norway have to
forage on both food types in preparation for onward
migration and the breeding season.
Taking into account the digestibility and retention time
of each food type along with the need to maximise the
amount of energy and nutrients acquired during the stop-
over, we would expect geese feeding on pasture and
stubble fields to switch between periods of feeding and
periods of digestion, with the latter being associated with
bouts of resting. In contrast, geese feeding on grain may
forage more or less continuously. Furthermore, since geese
are most vulnerable to predation while feeding (Prop and
Vulink 1992) and since they do not feed during the night
(Madsen et al. 1997), we would expect the number of geese
feeding on grass and stubble to peak during the morning
and afternoon, with a minimum around noon when birds
will likely be digesting at the relatively predator-safe and
undisturbed roosting sites. This U-shaped response has
already been shown for other wildfowl species, such as the
Whooper Swan Cygnus cygnus (Rees et al. 2005), Swan
G\goose Anser cygnoides (Fox et al. 2008b), Lesser White-
fronted Goose Anser erythropus (Fox et al. 2008a), White-
fronted Goose Anser albifrons (Owen 1972) and Pink-
footed Goose feeding on winter wheat (Therkildsen and
Madsen 2000b).
Other factors, such as distance between the roost and the
foraging habitat, disturbance and flock size can also
influence goose behaviour (Ladin et al. 2011; Madsen et al.
2009; Therkildsen and Madsen 2000b; Tombre et al. 2005).
The combination of different independent variables may
also have a significant effect on feeding activity (Rees et al.
2005). The aim of this study was to analyse the activity
patterns of the Pink-footed Goose in relation to potential
explanatory variables. We hypothesised that the proportion
of geese feeding in a flock would increase with proximity
to the roost, which is considered to be a relatively undis-
turbed and safe refuge from predators. We also assessed
whether geese exposed to a sporadic and unpredictable
disturbance (e.g. intentional scaring, dogs or passing trac-
tors) differ significantly in their behavioural responses to
those subjected to a more consistent, predictable distur-
bance (e.g. constant traffic at a fixed distance from the
flock) and those in undisturbed conditions. In particular, we
hypothesised that geese would become less readily habit-
uated to the unpredictable conditions and expected an
increase in the proportion of vigilant geese in areas sub-
jected to a sporadic disturbance, combined with a lower
proportion of feeding individuals. Due to shared vigilance,
the proportion of vigilant individuals was expected to be
smaller in larger flocks.
When taking into account the fact that digestion rates
differ for different food types and that geese need to gain
646 J Ornithol (2013) 154:645–654
123
enough energy and nutrients before they continue their
migration, we hypothesised that: (1) there is diurnal vari-
ation in the number of geese feeding on grass and stubble
fields, with peaks in the morning and the afternoon; (2)
there is no diurnal variation in feeding activity for geese
feeding on grain; (3) the proportion of feeding geese
decreases with distance to roost; (4) the proportion of
vigilant geese is higher when disturbance is less
predictable.
Methods
Study population and area
The Svalbard Pink-footed Goose breeding population
overwinters in Belgium, The Netherlands and Denmark.
During their migration to their breeding grounds the geese
stop in mid-Norway (Trøndelag) and northern Norway
(Vesteralen) (Madsen et al. 1999), with the first arrivals
appearing in Trøndelag in early April, reaching a peak
during late April–early May (Madsen et al. 1999). The
geese stay in Trøndelag for an average of 20 days before
migrating further north (Bauer et al. 2008). The popula-
tion has grown from 15,000 individuals in the 1960s to
80,000 in 2012 (Fox et al. 2005; J. Madsen, unpublished
data).
Trøndelag is a semi-mountainous area that is charac-
terised by a mosaic of agricultural fields and forests. The
area is rich in lakes and fjords, both of which serve as
roosting sites for the geese (Fig. 1). Pink-footed Geese
spend the night at roost sites and feed in fields during the
day. Around midday the majority of the staging popula-
tion returns to the roosts (Madsen et al. 1997). However,
small numbers are observed on the roosts all day long.
Pastures are widely available throughout the stopover
season, whereas stubble fields are gradually ploughed in
late April–early May and subsequently sown with spring
cereals (Madsen et al. 1997). Geese arriving from the
wintering grounds at the beginning of the stopover season
therefore forage on pasture (including undersown barley
stubble) and barley stubble from the preceding autumn,
whereas newly sown barley and germinating grains
become an increasingly important food source towards the
end of the stopover season. Hereafter we refer to these
habitats as grass, stubble and grain, respectively. It is not
known whether geese foraging on stubble mainly feed on
waste/spilt grain from the previous year and/or germi-
nating grain and weeds, so we decided to keep stubble as
a separate habitat type. Geese are also occasionally
observed on waste potato fields and ploughed barley
stubble, where they probably feed on leftover potatoes
and grain, respectively.
Behavioural observations
Field observations were conducted between 15 April and
15 May 2011. A total of 171 independent half-hour scans
of flock activities were carried out between 0500 and
2100 hours, using standard flock scanning methods (Alt-
mann 1974), as described below. All scans were performed
during hours of daylight. Flocks were observed on roosts
and in three different field habitats: grass, stubble and
grain. On the fields we recorded agonistic, watching (goose
with head up, either standing or sitting, believed to reflect
number of vigilant individuals), feeding, flying, preening,
resting (goose with head under wing) and walking activi-
ties. On the roosts we recorded agonistic, watching, flying,
preening, resting, walking, swimming, courtship and
drinking activities. For each scan a group of 45–70 indi-
viduals was selected at random from the flock and observed
for 30 min. Within each half-hour scan the number of
individuals engaged in the different activities was recorded
at 5-min intervals. Our aim was to observe the same
individuals throughout the scan; therefore, to keep track of
the same birds we picked a distinct environmental feature
(big stone, tree, terrain, distinct feature in the background,
etc.) as a starting point for the scan. As the observations
made in the consecutive 5-min intervals were not inde-
pendent, those recorded within each half-hour observation
Fig. 1 Study area showing the location of flock scans (black dots)
and roosting areas (black squares). Light-grey area Water
J Ornithol (2013) 154:645–654 647
123
period were averaged to avoid pseudoreplication in the data
(Ladin et al. 2011). The number of observed individuals
was independent of the time of day, date and flock size (all
scanned flocks consisted of[60 individuals). For as long as
each specific habitat was present in the area, the observa-
tion effort was evenly distributed between the three main
habitats used by the geese to ensure that they were
observed equally throughout the day and over the season.
The observation effort was also distributed evenly over the
study area. With these exceptions, the observed flocks were
selected at random. Scans were considered to be indepen-
dent when the interval between consecutive scans was at
least 1 h or scans were conducted in two different loca-
tions. For each scan the size of the entire flock and the
disturbance level at the site were also recorded. The dis-
turbance level was categorised as unpredictable (at least
one disturbing event taking place \200 m from the flock:
people or dogs passing, cars, trains or bikes passing at
irregular intervals, loud engine noise, predators, active
scaring by farmers), predictable (cars passing continuously
on a road\200 m from the flock and none of the disturbing
events from the ‘unpredictable’ category present during the
scan) and no disturbance (no disturbing events within
200 m from the flock). Distances to the closest roost site
and distances to roads were measured using ArcGIS ver. 10
(ESRI 2010).
Statistical analyses
In order to examine the activity pattern of the geese, we
constructed a generalised linear model (GLM) for each
behavioural activity. We used the proportion of scanned
birds performing that behaviour as the dependent variable
to correct for non-equal numbers of observed birds during
the 5-min records. For birds in the fields, each full model
included the following independent variables: time of day
(1st–4th order polynomials), flock size, distance to the
closest roost site, habitat type (excluding roost) and dis-
turbance level. The inclusion of polynomials allowed for
non-linear relationships between number of geese and time
of day. Each full model also included all two-way inter-
actions between each of the categorical variables (habitat
type and disturbance) and the continuous variables (time of
day, distance to roost, flock size). Prior to analysis, distance
to roost was log10-transformed to obtain a linear relation-
ship with the dependent variables. Time of day was
z-transformed to achieve a mean of zero and a standard
deviation of 1 (Schielzeth 2010). Each full model was
simplified by removing the least significant terms until
deletion of the next term did not result in a decrease in the
Akaike information criterion of [2 (Anderson et al. 2000;
Crawley 2007). Main terms were only removed if all
interaction terms that they were part of had been removed.
Various diagnostics of model validity and stability were
checked (variance homogeneity and normality of residuals,
collinearity and influence of outliers). The comparison
between categorical variables in the reduced models was
done based on a priori contrasts as described by Crawley
(2007). The ‘no disturbance’ category and grain habitat
were chosen as reference points for the models because
these factors were considered likely to differ from the
others for reasons described in the ‘‘Introduction’’.
We applied a similar method to examine the diurnal
activity pattern of geese at roost sites. Here, the full models
included the independent variables flock size, disturbance
level, time of day (1st–4th order polynomials) and the two-
way interactions between disturbance level and other pre-
dictors. One model was run for each activity. All statistical
analyses were performed in R 2.13.1� (Development Core
Team 2011).
Results
Diurnal behaviour in fields
In total, 128 half-hour scans were analysed. For geese in
the fields only the models for feeding and watching could
be further analysed, as the others did not fulfil the
assumptions of the GLM (residuals were not normally
distributed). However, geese observed in fields were pre-
dominately engaged in feeding and watching (feeding:
71 %, watching: 21 % of the time).
The proportion of geese seen feeding was highest on grain
and in undisturbed areas and lowest on grass and in areas
where there was an unpredictable disturbance (Fig. 2a, b).
Overall, habitat and disturbance level explained 27 % of the
variance in the model (Table 1, model a). The proportion of
feeding geese was highest around noon for all three habitats
and lowest during the morning and afternoon (Fig. 3). The
proportion of geese feeding was significantly negatively
correlated with distance to roost but not correlated with
flock size (Pearson’s correlation: r = -0.35, p \ 0.001;
r = 0.11, p = 0.24, respectively). Overall, the most parsi-
monious model describing diurnal variation in the propor-
tion of geese feeding (F10,117 = 6.76, p \ 0.001) accounted
for 41 % of the variance (Table 1, model a).
The proportion of geese watching was related to the
time of day, with peaks in the morning and afternoon for
those geese foraging on grass and stubble but with a rela-
tively stable response for geese foraging on grain (Sq. time
of day 9 habitat; Table 1, model b; Fig. 4). The proportion
of watching birds was lower for those foraging on grain
than for those foraging in other habitats (Figs. 2c, 4). The
proportion of watching geese was largest in areas exposed
to an unpredictable disturbance and smallest on
648 J Ornithol (2013) 154:645–654
123
undisturbed fields (Fig. 2d). Overall, the predictors had a
significant effect on diurnal variation in the proportion of
watching geese (F8,119 = 7.75, p \ 0.001) and the model
explained 34 % of the total variance.
Diurnal behaviour on roost sites
In total, 43 half-hour scans were analysed. For geese on
roost sites the models for resting, watching, preening and
walking all fulfilled the assumptions of the GLM. In the
models for preening and walking all terms could be
removed during model simplification, and these models are
therefore not discussed further.
The proportion of resting geese was highest around noon
(Fig. 5a; Table 1, model c). The most parsimonious model
explained 51 % of the variance (F2,41 = 6.83, p = 0.003).
The proportion of watching geese was lowest around noon
(Fig. 5b; Table 1, model d). Overall, the model explained
54 % of the variance (F2,41 = 19.33, p \ 0.001). Distur-
bance was not a significant predictor for any of the
behavioural categories for roosts (Table 1, models c, d).
Changes in flock size according to distance to roost,
disturbance and time of day
For fields, goose flocks were largest and closest to the roost
in the early afternoon (Table 1, model e; Fig. 6a; Pearson’s
correlation: p = 0.01, r = 0.23). The largest flocks were
found foraging under a predictable disturbance; however,
the flock size did not differ between unpredictably dis-
turbed and undisturbed fields (Fig. 6b). Flock size was not
correlated with the proportion of feeding (Pearson’s cor-
relation: r = 0.11, p = 0.24) or watching (r = 0.23,
p = 0.37) geese.
Discussion
The behaviour of the observed Pink-footed Goose varied
with time of day, habitat type, distance to roost and dis-
turbance level. Contrary to expectation and in contrast to
the results of other studies, the proportion of feeding geese
peaked around noon for all three studied field habitats.
0.0
0.2
0.4
0.6
0.8
1.0 *** r **
0.0
0.2
0.4
0.6
0.8
1.0 *** * r
0.0
0.2
0.4
0.6
0.8
1.0
grass grain stubble
** r **
0.0
0.2
0.4
0.6
0.8
1.0
unpredictable predictable no disturbance
* * r
0.2
0.4
0.6
0.8
1.0
Pro
port
ion
of fe
edin
g ge
ese
(a)
grass grain stubble
*** r **
0.0
0.2
0.4
0.6
0.8
1.0
(b)
unpredictable predictable no disturbance
*** * r
0.0
0.2
0.4
0.6
0.8
1.0
Pro
port
ion
of w
atch
ing
gees
e (c) ** r **
0.0
0.2
0.4
0.6
0.8
1.0
(d) * * r
Fig. 2 Mean proportion of Pink-footed Goose Anser brachyrhynchusindividuals feeding and watching in different habitats (a, c) and under
different disturbance levels (b, d). Horizontal bold lines Mean values
in the proportion of geese in a given behavioural category, vertical
dashed lines 1.5-fold the interquartile (IQR) range of data, circlesoutliers outside IQR. The results of the analysis of variance:
*p \ 0.05, **p \ 0.01, ***p \ 0.001, r reference
J Ornithol (2013) 154:645–654 649
123
Therkildsen and Madsen (2000b) found only slight diurnal
changes in the proportion of feeding Pink-footed Goose,
with a noon peak on grass and morning/afternoon peaks on
winter wheat. Studies on other goose species have found
U-shaped feeding patterns (Fox et al. 2008a, b; Owen
1972). However, all of these studies deal with the behav-
iour of geese in wintering areas or during the early spring
before migration to the breeding grounds. One explanation
for the opposite pattern in our study could be that geese
change from a wintering behaviour, when staying lean is
more convenient due to decreased predation risk and
reduced cost of flying, to a pre-breeding behaviour, when
sufficient reserves have to be obtained over a short period
to facilitate migration to the breeding grounds and the
beginning of reproduction (Drent et al. 2003).
The observed pattern in proportion of feeding birds also
suggests that goose feeding behaviour is not solely driven
by the physiology of digestion but, according to our model,
is also influenced by disturbance, distance to the roost and
flock size. Disturbance is often viewed as a factor that
prevents birds from foraging on particular fields, and some
studies have shown that birds in disturbed areas have
reduced fitness (Klaassen et al. 2006; Madsen 1994). Our
results suggest that even a disturbance that does not force
the geese to flee can have an effect on their behaviour.
Furthermore, we found that a sporadic and unpredictable
disturbance reduced the proportion of birds feeding com-
pared with undisturbed geese or those exposed to a pre-
dictable disturbance. Geese that are frequently forced to
feed under conditions of sporadic disturbances may there-
fore experience a reduction in fitness. We also found a
difference in the proportion of birds feeding under a con-
dition of no disturbance and a condition of predictable
disturbance. Birds are believed to habituate more easily to
a frequent and directional disturbance than to an unpre-
dictable and sporadic one (Madsen et al. 2009; Rees et al.
2005). Assessing habituation was not an aim of this study,
and our data did not enable us to test this directly, but the
finding that the proportion of watching birds was lower for
undisturbed fields than for fields exposed to a predictable
disturbance suggests that constant road traffic is still an
important disturbing factor, despite larger flocks occurring
in the latter case. As expected, the proportion of feeding
geese was inversely related to distance to roost. In addition,
foraging next to the roost maximizes the time spent feeding
by avoiding lengthy flights to distant areas.
During the mornings and afternoons, few flocks were
observed at roost sites as most of the geese were foraging
in the fields. The opposite pattern was observed around
noon, when most of the geese abandoned the fields for
roost sites (M. Chudzinska, personal observation; Madsen
et al. 1997). The observed peak in the proportion of geese
feeding around noon therefore relates to a relatively small
subset of the geese that stage in Trøndelag. We found the
largest flocks in the middle of the day and close to the
roosts. Due to increased foraging pressure in the vicinity of
roosts, habitats next to roosts may be the first to become
depleted. The large local concentration of almost the entire
Pink-footed Goose population may force birds to fly further
and feed in smaller and more dispersed flocks in the
morning and afternoon when most of the geese are forag-
ing. Therefore, because geese have to fly for longer periods
of time at the cost of lost feeding time and increased energy
expenditure, density dependence may indirectly mediate
the foraging pattern observed in Trøndelag.
Table 1 The final reduced models describing both diurnal variations
in the behaviour of the Pink-footed Goose Anser brachyrhynchus and
diurnal variations in observed flock size
Final reduced models df Sum of
squares
F p value DR2
Model a: Response—proportion of geese feeding in fields
Time of day 1 0.03 1.4 0.23 0
Sq. time of day 1 0.07 3.6 0.06 0.05
Habitat 2 0.47 12.2 \0.001 0.14
Disturbance 2 0.50 12.8 \0.001 0.13
Distance to roost 1 0.07 3.6 0.06 0.03
Flock size 1 0.04 1.9 0.17 0.02
Time of
day 9 habitat
2 0.14 3.6 0.03 0.04
Residuals 117 2.26 R0.41
Model b: Response—proportion of watching geese in fields
Time of day 1 0.01 0.02 0.91 0.01
Sq. time of day 1 0.23 16.5 \0.001 0.10
Habitat 2 0.32 11.0 \0.001 0.13
Disturbance 2 0.22 7.7 \0.001 0.10
Sq. time of
day 9 habitat
2 0.12 4.1 0.02 0.01
Residuals 119 1.70 R0.34
Model c: Response—proportion of resting geese at roost sites
Time of day 1 0.06 1.0 0.33 0.00
Sq. time of day 1 0.77 12.7 \0.001 0.51
Residuals 41 2.45 R0.51
Model d: Response—proportion of watching geese at roost sites
Time of day 1 0.01 0.01 0.99 0.00
Sq. time of day 1 0.96 38.7 \0.001 0.54
Residuals 41 0.99 R0.54
Model e: Response—flock size
Time of day 1 284 9.44 0.01 0.06
Sq. time of day 1 176 5.85 0.02 0.03
Disturbance 2 221 3.67 0.03 0.06
Distance to roost 1 257 8.53 0.01 0.06
Residuals 122 3,675 R0.20
650 J Ornithol (2013) 154:645–654
123
Seasonal changes in habitat availability may also influ-
ence the feeding behaviour of the geese. Grass is accessible
throughout the entire staging period, whereas stubble fields
are almost completely replaced by newly sown grain fields
about 1 week before the geese leave the area. By then,
geese may be under stronger pressure to find high-quality
food and may therefore increase the amount of time they
spend feeding on the high-energy grain fields prior to
departure. Since it was impossible to follow the same flock
of geese throughout the day and season and to know when
they arrived in Trøndelag, we cannot establish a diurnal
activity budget for individual birds. This can only be done
by keeping track of individually marked birds (by collars or
transmitters), and this will be addressed in a subsequent
study. Detailed data on diurnal variation in the spatial
distribution of geese and habitat availability are necessary
to further study the effect of variation in population density
and the effect of seasonal habitat changes.
Contrary to expectation, we found no relationship
between the proportion of watching birds and flock size, as
was reported by Inglis and Lazarus (1981). Our results
indicate that disturbance level may have a higher influ-
ence on the proportion of vigilant birds than flock size
itself.
The proportion of birds resting at roost sites peaked at
noon as predicted, in agreement with Fox et al. (2008b).
We did not find any diurnal changes in the proportion of
resting geese on fields, whereas such changes were found
by Therkildsen and Madsen (2000b) who observed noon
resting peaks for grass and winter wheat. Due to the high
number of fjords and lakes that provide roost sites in the
study area, we presume that geese choose roosts rather than
0.0
0.2
0.4
0.6
0.8
1.0
Unpredictable
Gra
ss
0.0
0.2
0.4
0.6
0.8
1.0
Pro
port
ion
of fe
edin
g ge
ese
Gra
in
0.0
0.2
0.4
0.6
0.8
1.0
5 7 9 11 13 15 17 19 21
Stu
bb
le
Predictable
5 7 9 11 13 15 17 19 21
Time of day
No disturbance
5 7 9 11 13 15 17 19 21
Fig. 3 Diurnal changes in the proportion of feeding geese on different field habitats and exposed to different disturbance levels. Circles Mean
values for flock scans, curves model predictions (solid lines) with 95 % confidence intervals (CI; dashed lines)
J Ornithol (2013) 154:645–654 651
123
0.0
0.2
0.4
0.6
0.8
1.0
Unpredictable
Gra
ss
0.0
0.2
0.4
0.6
0.8
1.0
Pro
port
ion
of w
atch
ing
gees
eG
rain
0.0
0.2
0.4
0.6
0.8
1.0
5 7 9 11 13 15 17 19 21
Stu
bb
le
Predictable
5 7 9 11 13 15 17 19 21
Time of day
No disturbance
5 7 9 11 13 15 17 19 21
Fig. 4 Diurnal changes in the proportion of watching geese on different field habitats and exposed to different disturbance levels. Circles Mean
values for flock scans, curves model predictions (solid lines) with 95 % CI (dashed lines)
0.0
0.2
0.4
0.6
0.8
1.0
Pro
port
ion
of r
estin
g ge
ese
5 7 9 11 13 15 17 19 21
Time of day
(a)
0.0
0.2
0.4
0.6
0.8
1.0
5 7 9 11 13 15 17 19 21
Time of day
Pro
port
ion
of w
atch
ing
gees
e
(b)
Fig. 5 Diurnal changes in the proportion of geese resting (a) and watching (b) on roost sites with predicted values (solid lines) and 95 % CI
(dashed lines). Circles Mean values for flock scans
652 J Ornithol (2013) 154:645–654
123
fields for resting as they may be affected by disturbance
and predators in the latter. Roost sites are usually located in
undisturbed areas, further away from traffic.
In conclusion, we showed that there is diurnal variation
in the behaviour of the Pink-footed Goose on fields and at
roost sites. This variation may be explained by a combi-
nation of high physiological demands, anthropogenic dis-
turbance and environmental factors. The results of this
study, combined with a planned follow-up study on diurnal
changes in habitat choice and the local movements of
flocks and individuals, provides us with the necessary input
for establishing a diurnal energy budget. This variable is
necessary for investigating the behavioural trade-offs in
habitat and site selection that geese make along their
migratory route to optimise their fitness. Our findings
suggest that the design of protected areas should consider
the predictability of disturbance rather than just the pres-
ence/absence of possible disturbing factors.
Acknowledgments This study was part of M.C.’s PhD project
funded by Aarhus University. The fieldwork was supported by the
Norwegian Research Council project MIGRAPOP. We would like to
thank Per Ivar Nicolaisen and Flemming Hansen for help during the
data collection. We also thank Eileen Rees and an anonymous
reviewer for valuable comments on the manuscript. All field methods
used in this study comply with the current laws of the country in
which they were performed.
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