Comparative Spring Habitat and Food Use by Two Arctic Nesting Geese

15 Pages·1999·6.8 MB·English

by  Suzanne Carrière

A
Wilson Bull., 111(2), 1999, pp. 166-180
COMPARATIVE SPRING HABITAT AND FOOD USE BY TWO
ARCTIC NESTING GEESE
SUZANNE CARRIERE,' 25 ROBERT G. BROMLEY,'^ AND GILLES GAUTHIER'
—
ABSTRACT. The timing of egg laying is generally constrained by female condition, which is partly deter-
mined by the food available to her before laying. Although it was generally believed that geese rely exclusively
on internal nutrient reserves for egg production, spring feeding is intensive in many populations of geese,
significantly adding nutrients necessary for egg production and incubation. We compared the spring feeding
ecology ofGreater White-fronted Geese {Anseralbifronsfrontalis) and Canada Geese {Brantci canadensis hutch-
NWT
insii) on a shared nesting ground on the Kent Peninsula, (68° N, 108° W), where pairs feed intensively
from arrival until incubation. Live plant biomass did not significantly increase within specific habitats during
preincubation, but the total available biomass was greater after snow melt because habitats with higher biomass
became available. Live plant biomass available in pond margins (30—60 g/m-) was 4-15 times higher than in
habitats that were available earlier, i.e., mud-flats and hummocks (4-8 g/m-). Before snow melt, both species
shared the 1-20% of the study area that was snow free (max. density 600 pairs/km-), opportunistically used the
only two available habitats, mud-flats and hummocks, and primarily ate (50-70%) tillers of Puccinellia spp.
During snow melt, pairs dispersed, pair density decreased (max. of 40 pairs/km-), and interspecific differences
in habitat and food use appeared. White-fronted Geese used pond margins and ponds more often than Canada
Geese. After snow melt. White-fronted Geese predominantly fed in ponds on Carex spp. and Dupontia fisheri
rhizomes and basal stems; Canada Geese continued feeding opportunistically, pecking leaves in all habitats and
grubbing rhizomes in pond margins and ponds. White-fronted Geese used the grubbing technique more often
than Canada Geese in all habitats and periods. Received 13 Feb. 1998. accepted 17 Nov. 1998.
Energy investment by females in reproduc- Strategy to facilitate early nesting is to carry
tion is highest during the period of egg for- nutrient reserves accumulated during migra-
mation in birds with precocial young, such as tion to the breeding grounds (Ankney and
geese (King 1973). Clutch size and timing of Macinnes 1978, Wypkema and Ankney 1979,
laying are potentially constrained by female Ankney 1984, Budeau et al. 1991, Bromley
condition, which is partly determined by the and Jarvis 1993, Choiniere and Gauthier
amount of energy and nutrients available to 1995). There is, however, an upper limit to the
her before egg formation (Drent and Daan amount of reserves that can be economically
1980, Winkler and Walters 1983). carried during migration (Lindstrom and Al-
Early nesting is critical for Arctic nesting erstam 1992).
geese because of the short summer and the In migratory birds, the timing of rapid fol-
rapid seasonal decline in components of re- licular development (RED) initiation with re-
productive success such as gosling growth and spect to spring migration may affect the rel-
probability of producing recruits (Barry 1962, ative contribution to egg production of nutri-
Cooke et al. 1984, Cooch et al. 1991, Sedinger ents acquired en route versus those acquired
and Flint 1991, Lindholm et al. 1994). One on nesting grounds. Timing of RED initiation
directly determines laying date of the first egg
(reviewed by Rohwer 1992). Because some
Uni'vD.epLta,vadle, QBuieobleogci,cQeCt,CGenItKre7dP’4E,tuCdaensadNao.rdiques, female geese in some locations typically nest
’ Present address: Wildlife and Fisheries Division, soon (3-6 days) after their arrival on the nest-
Dept, of Resources, Wildlife, and Economic Devel- ing ground {Anser rossii: Ryder 1970; Anser
opment, Government of the Northwest Territories, 600 caerulescens caerulescens: Ankney 1977, An-
5102-50 Avenue, Yellowknife, NT XIA 3,S8, Canada. kney and Macinnes 1978; Anser canagica:
’ Wildlife and Fisheries Division, Dept, of Resourc- Thompson and Raveling 1987; Branta berni-
es, Wildlife, and Economic Development, Government cla bernicla: Spaans et al. 1993), RED is ini-
of the Northwest Territories, 600 5102-50 Avenue,
Yellowknife, NT XIA 3S8, Canada. tiated before arrival, hence the date of nest
Present address: Box 177, Yellowknife, NT XI initiation is independent of food availability
1
2N8, Canada. on the nesting ground (Raveling 1978, Ank-
^ Corresponding author; ney 1984, Newton 1977; but see Prop and de
E-mail: [email protected] Vries 1993).
166
Carriere el al. • SPRING FEEDING BY ARCTIC GEESE 167
In other populations most female geese lay We compared the feeding ecology of Great-
at least 12 days after an'ival on the nesting er White-fronted Geese (Anser albifronsfron-
grounds, long enough for the completion of talis) and Canada Geese {Branta canadensis
RFD of the first egg [Branta bernicla nigri- hutchinsii) during preincubation. These spe-
cans: Raveling 1978; B. canadensis: Macln- cies have similai' body mass (White-fronted
nes et al. 1974, Bromley 1984; A. albifrons: Goose 8% > Canada Goose; R.G.B., unpubl.
Fox and Madsen 1981, Budeau et al. 1991; A. data), reproductive chronology, and share the
caenilescens caerulescens (at La Perouse same Arctic spring feeding and nesting
Bay): Findlay and Cooke 1982; A. c. atlantica: grounds on the Kent Peninsula, NWT, Canada.
Gauthier and Tardif 1991]. In this case, food Our objectives were to determine (1) how
availability on the nesting ground can affect snow melt affected the availability of feeding
the date of RFD initiation, the date of nest habitats and plant biomass, (2) whether
initiation, and potentially clutch size and con- White-fronted and Canada geese differed in
stancy of incubation. Most of the energy nec- their use of habitat and food during preincu-
essary for egg formation and laying was met bation on a shared nesting ground, and (3)
by food on the nesting grounds for A. albi- how changes in habitat and food availability
frons frontalis (Budeau et al. 1991), B. can- resulting from snow melt affected dispersal,
adensis occidentalis (Bromley and Jarvis habitat and food use, and the timing of nesting
1993), and A. caerulescens atlantica (Choin- in these two species of geese.
iere and Gauthier 1995). Intermediate cases
STUDY AREA AND METHODS
may occur where the time available for feed-
ing between arrival on the nesting ground and The study was conducted on the Walker Bay Study
laying varies greatly among females and/or Area (68° 22' N, 108° 04' W), southwest Kent Penin-
among years within populations (Raveling sula, Northwest Territories (Eig. 1), as part oflongterm
studies on the breeding ecology of White-fronted and
1978).
Canada geese (see Bromley et al. 1995). The shallow
Food availability in the Arctic in spring was plain of the river valley is a high density nesting area
traditionally thought to be so low that, al- for both species of geese (Bromley et al. 1995).
though female geese could feed, they could Studies of the feeding ecology during preincubation
not meet their energy requirements for daily were made on an intensive study area positioned to
maintenance or egg production (Barry 1962, permit semicontinuous observation of geese in spring
while minimizing disturbance caused by human move-
Ryder 1970; reviewed by Rohwer 1992). For
some species, body mass of females generally msietnest:ssi(tEeigA. 1()0..7T2hekma-r)eawawsasrefpurretsheenrtadtiivviedeodfitnhteohtawbo-
increases before or during egg production itats found all along the river and typical of areas in
(Wypkema and Ankney 1979, Budeau et al. which arriving geese concentrated until snow melt; site
1991, Bromley and Jarvis 1993, Choiniere B (4.33 km-) was representative of the rest of the gen-
and Gauthier 1995) indicating that energy in- eral study area where nesting typically occurred. Site
take during these periods could at least meet A, a raised levee paralleling the river, was drier than
site B. Habitats available to geese were classified from
requirements for daily maintenance (Ganter
dry to wet: hummock, mud-fiat, pond margin, and
and Cooke 1996, Carriere 1996). Further, var- pond (see plant list per habitat in Carriere 1996). Mud-
iation in timing of nesting can be related to fiat habitats were sparsely vegetated flats of exposed
variation in food availability prior to egg for- glacial marine sediments (ca 3000 yrs ago; Dyke and
mation (Prop and de Vries 1993). Thus, food Dredge 1989), largely saline clays and silts. Hummock
availability and use in the Arctic in spring habitats were formed by frost heaves (5-30 cm high)
and covered by thin soil where Salix spp. dominated.
clearly is significant. Pond margins were the edges of depressions that were
In the Arctic, food availability during pre- wet from snow melt to early June, had low salinity,
incubation is highly variable. This variation and formed meadows dominated by graminoids and
hinders interspecific comparisons of feeding forbs. Pond habitats were depressions 0.10-1.00 m
ecology during preincubation because we can- deep, inundated at least until early July, and dominated
not differentiate between factors that are site by hydrophilic forbs. All habitats formed a fine grained
specific (e.g., weather, snow melt patterns, hmaobsiatiatc) woifthvarpiaotucshessha(pie.es.., Mcoonsttinpuaotucshesarecaosveorfedsa5m0e-
plant phenology) and species specific (e.g., 900 m-, with some mud-flats outside sites A and B
body size, bill moiphology; Prevett et al. extending more than 1—km-.
1985, Fox et al. 1992). Generalphenology. We recorded the phenology of
—
168 THE WILSON BULLETIN • Vol. Ill, No. 2, June 1999
Nests
White-fronted geese
1993
1994
Canada geese
1993
*
1994
—
Drumlin
^
Lake/Pond
Transect
Tower
FIG. 1. Walker Bay Study Area is situated in a valley near Walker Bay on the Kent Peninsula, NWT,
Canada. A section selected for detailed study was divided into 2 sites: site A was snow-free first in spring and
was typical of habitats available along the river banks. Snow melt phenology in site B was typical of the rest
of the study area.
snow melt, goose arrival, and goose dispersal along 11% of site A (2 stations) and 7% of site B (18 sta-
four 1 km transects (Fig. 1). At 2-3 day intervals we tions). At each station, we used binoculars to count
visually estimated snow cover (±5%) in 200 X 200 m and locate all geese that could be identified to species.
areas, situated in pairs, one on each side of the transect Preincubation was divided into three periods defined
at each of five stations 200 m apart. Thus, we covered by snow melt phenology on site A: (1) before snow
Carhere el al. • SPRING FEEDING BY ARCTIC GEESE 169
melt (snow cover >80%). (2) during snow melt (snow between the observed and unobserved areas during
cover = 20-80%)-—a period of rapid change, and (3) preincubation minimized pseudoreplication. For ex-
after snow melt (snow cover <20%). ample, no individual with a coded neck collar (from
—
Nesting phenology. Nests were located by observ- 1987-1994 banding operations; Bromley et al. 1995)
ing nest building behavior from towers. Date of the was observed in more than six different scans (only
first egg laid (i.e., date of nest initiation) was estimated 30% of collared individuals were observed more than
only for nests found during laying by subtracting 1.3 twice).
d per egg (R.G.B., unpubl. data) already laid. Nests For each year and period, interspecific differences
outside site A and B were located during ground sur- in habitat use were analyzed without reference to hab-
veys of randomly selected 1 km- plots (Bromley et al. itat availability using G-tests of independence, fol-
1995). We compared median laying dates for combi- lowed, when significant differences were detected, by
nations of years and species using Kruskal-Wallis AN- pairwise unplanned comparison tests (Sokal and Rohlf
OVA
on Ranks tests, followed by non-parametric mul- 1981 using Excel 97).
;
tiple comparison tests using Excel 97 following Daniel Habitat use was compared to availability before and
(1978). — after snow melt, but not during melting, because avail-
Habitat availability. We measured habitat avail- ability changed too rapidly, i.e., from 20% to 80%
ability in the areas at two towers (see below) by map- snow-free area in <7 d. We used X" goodness-of-fit
ping habitat patches with a 20 X 20 m grid in the field tests, followed by Bonferroni simultaneous confidence
and using aerial photographs. Availability of a habitat interval tests (Sokal and Rohlf 1981, Neu et al. 1974;
was defined by the cumulative area of all patches of using Excel 97) to detect sources of significant differ-
that habitat as a proportion of the total snow-free area. ences (design 1 in Thomas and Taylor—1990).
Only snow-free areas were considered accessible to Plant availability within habitats. We estimated
feeding geese (Hall et al. 1997).— food plant availability in snow-free habitats by sam-
Use and selection ofhabitats. We observed goose pling randomly 20 X 20 cm quadrats within habitat
pairs throughout preincubation from two towers in patches in site A and B, 4 times between 17 May-14
1993 and one tower in 1994. Daily observations were June throughout preincubation (1993: n = 120; 1994:
conducted from one tower at a time depending on the n = 218). We collected all above and below ground
distribution of geese in the study area. We used the vegetation 0.1-3 cm deep then froze each sample for
scan sampling method (Altman 1974), with scans con- transportation. Ground vegetation below 3 cm was
ducted every 2-6 hr during the 24 hr cycle. During a never thawed and was considered unavailable to geese.
scan, we observed all pairs present within 400 m of In the laboratory, live above and below ground vege-
the observation tower. Sections of sites A and B were tation was sorted by species, dried at 45° C to constant
visible from both towers (Eig. 1). Eor each pair, we mass, and weighed. We pooled plant species according
noted sex, behavior, and habitat used by each pair to food plant categories used in the analysis of feces
member. Sex was determined using relative neck size (see below). Availability of each food plant category
(larger in males), abdominal profile (larger in females in each habitat was defined as the average proportion
with developing follicles; Owen 1981, Eox et al. of total dry biomass represented by that category in
1995), and alert position (male usually standing high- each habitat during each snow melt period (Eig. 2).
er). Pairs were recorded as feeding when either the We analyzed total (pooled species) above and below
female or both members were grubbing (on below- ground biomass separately. We first analyzed differ-
ground plant parts), pecking (on above-ground plant ences in total biomass among habitats and sampling
parts), searching for food (moving with head down), dates for each year separately using Kruskal-Wallis
ANOVA
or drinking. on Ranks tests, followed by multiple com-
We calculated habitat use for each scan as the pro- parison tests to detect pairwise differences (Daniel
portion of observed feeding pairs using each available 1978). We then pooled sampling dates and analyzed
habitat. Pond and pond margin use data were pooled differences in biomass among habitats and years with
as wet habitats to obtain sufficiently large samples for Two Way ANOVA using square-root transformed data
a C-test (Sokal and Rohlf 1981). For analysis, we (Sokal —and Rohlf 1981).
pooled habitat use data within snow melt period and Diet We determined diet using two complemen-
.
tower. Habitat use data were assumed to be indepen- tary methods: (I) microhistological analyses of feces
dent within and between scans. This seemed reason- and (2) detailed observations of feeding techniques.
able for two reasons. First, preliminary observations Additional data were available from the esophageal
on focal individuals indicated that pairs showed little content of 16 female Canada Geese collected in 1994.
synchronization in movements between habitat patches Throughout preincubation, we collected all feces
(i.e., no group behavior). Second, because of the ex- that we could assign to an individual bird (i.e., a bird
treme patchiness of habitats, pairs could use all avail- that was observed defecating). Feces were individually
able habitats within 2 hr (minimum time interval be- frozen for transportation, dried in the laboratory, and
tween scans); 58% ofCanada Geese (n = 96) and 43% analyzed using microhistological techniques (see John-
of White-fronted Geese (/; = 69) individuals observed son 1982). We sampled four slides per feces, with 20
in focals used more than habitat patch within 10 min observation fields per slide. We identified most plant
I
(S.C., unpubl. data). The constant movement of pairs fragments (80-100% per feces) to genus. We grouped
170 THE WILSON BULLETIN • Vol. Ill, No. 2, June 1999
(/)
CO
CT3
E
g
1q
40
O
20
^
0
^
20
^
40
60
40 Pond
20 A
0
20
40
60 IAfter(20)
/’ ^ #Q' i S' -3 d e
^ i Si <tr i s- §
0)
(3
's/ U7 S'
1 1 J 1 _l L
Mud-flat Hummock Margin Pond
FIG. 2. Relative availability ofplants in each snow-free habitat before, during, and after snow melt, measured
as the average percent food in dry biomass on the Walker Bay Study Area, NWT, May-June 1993-1994. Sample
sizes are given in parentheses, years pooled. Availability of aboveground plant parts is given above the zero
line and of below ground plant parts below the zero line.
some rare food plants of the same genus or family that within feces ranged from less than 5% for graminoids
were growing in the same habitat (Table 1, Fig. 2). to 10—20% for dicots. We defined diet as the average
The validity of the identification of plant fragments in percent of each food plant (% of fragments) present in
feces was assessed by analyzing plant mixtures of the feces (frequency of occurrence method; Johnson
known composition (Holechek and Gross 1982) and 1982). Diet was determined for each goose species and
by comparing fecal results to esophageal contents of snow melt period by pooling years, with individual
female Canada Geese (Carriere 1996). We could not feces representing sampling units.
easily differentiate Sali.x arctica from Potentilla nivea, We compared use ofeach food plant among all pos-
nor discriminate Dupontiafisheri and Eriophorum spp. sible combinations of goose species and snow melt
from some fragments of other Gramineae and Cyper- periods using Kruskall-Wallis ANOVA on Ranks tests
aceae, respectively. Potentilla spp. and Eriophorum followed, if significant, by multiple comparison tests
spp., however, were relatively rare on the study area (Daniel 1978) using Excel 97.
—
(Fig. 2, see other Dicots and Eriophorum spp.). Some Feeding techniques. Use of below ground plant
below ground plant parts could not be identified reli- parts was indexed by the proportion of feeding pairs
ably (Carriere 1996). Feces analyses consequently pro- grubbing in each habitat during scans. Conversely,
vided only an estimate of use of common above pairs were assumed to eat above ground plant parts
ground food plants on our study area. Coefficients of while pecking.
variation of the proportion of food plants among slides We used a Paired ?-test to determine if the propor-
Carriere et ui • SPRING FEEDING BY ARCTIC GEESE 171
^00
0—0 ^
sO
Study
incubating
'sO
Bay
the GN \n ^ — o
Walker so
and o
incubation. snow-melt,
SO so
Ov
_ _ n
to o m O (ON o OoI o
after o o o o O o o o
d d d d d d d d
grounds V A V V V
and
o
ro o^ ov vnO VnO
VO ot
during
nesting
U
CQ 02
< U < U
02 02
n
the females (N lo in in •rt
on Ov Urn o(vN m 1^ n n u IT)
arrival
m U
“pre-laying” m < u <
02 00
o — — — n
ro (N Q.
from £
o O
rt (N u spp.
r^i (N
Hippiiris
snow-melt, snow-melt,
02
U < <
m — — < < leaves. and
in
"3O
after m m 42 and sp..
before in u in (I u SO
r-
§•O Etymus
and shoots,
U of
U u
collected CQ CQ young
< < <
02 02 PP those
during, — — —
r't in in VO in
were in u cs o in in rhizomes, except
before, (N (^1
rhizomes
includes
geese females p<a U < <—PP (0<2J OP all
so r'
and
conges/us,
o
rn "00 On ri u ntn ro
Canada
“Arriving” 5. spp..
U sp.:
and U u Eriophorum
PP
— fn o ri A A < )5 ^ ' Senecio
1993—94. of
White-fronted rri- riin srio n os X- ; ^• Cl: -,S lelniphylla.dicots,
“S3
of
<u
NWT, c/) P ^ O. I Q I //.
of <CUJ 5N i5= at/5.2 or fragments
OX) ^5 V) . .
1Diet. Peninsula, snow-melt. 1CGC3) =“(u C5; S =>,:“ <on iS ^s^S£ --SSJ-vWulf.turisincludes
Kent after O ic: oE0u3 ocj da.^Si oU^«D S"-oO ; Os cL S S^' sp.:
TABLE Area, female a,k•)t: Oi:'t^: O'ij^Q0V^3S2-:GD"OOJ 5X.: Oo T3 Oy HfippiirisUnidentified 'ttr=acre.
172 THE WILSON BULLETIN • Vol. Ill, No. 2, June 1999
10
O
8 .2
c
6 <0
to
ca>
4
o
%
2
E
D
z
0
10
6
4
0)
2
E
3
Z
0
Date
LIG. 3. Number of individual White-fronted Geese (WL) and Canada Geese (CG) counted daily at each
station on sites A (/; — 2) and B (// = 18; see Lig. 1), from arrival to early incubation, and number of nests
initiated daily by each species on the Walker Bay Study Area, NWT, 1993-1994. Arrows indicate duration of
rapid follicular development (RED) for a first egg layed at the median laying date each year. Shaded areas
indicate periods of snow melt, defined as 80-20% snow cover. Snow melt pattern on site A was used to define
periods for all analyses.
tion of time spent grubbing differed between goose RESULTS
species, pairing observations within habitat-period- —
year combinations. Lor each species, we used linear Annual phenology. Upon our airival on
regre.ssion to analyze how the proportion (arcsine 20 May 1993 and 17 May 1994, sites A and
square-root transformed in degrees; Sokal and Rohlf B were 95% and 99% snow covered, respec-
1981) of time spent grubbing changed with the pro- tively. Hummock and mud-flat habitats locat-
portion of below ground biomass available in different ed along the river were the only habitats avail-
habitats, snow melt periods, and years. The short, rapid able. Relative to 1987-1996 (R.G.B., unpubl.
melting period in 1994 was combined with the after- data), snow melt was early in 1994 and av-
melt period.
Unless otherwise stated, statistical analyses were erage in 1993 (Fig. 3). In general, snow melt-
performed using SigmaStat® (version 1.0; Jandel Sci- ed first on dry habitats (mud-flat, hummock),
entific Software 1993) in the PC DOS and Microsoft® then on wet ones (pond margin, pond), and
Windows® operating system. Statistical significance earlier on site A than on site B (Fig. 3). The
was established at P < 0.05. periods before snow melt were 10 days (1993)
Carriere el al. • SPRING FEEDING BY ARCTIC GEESE 173
and 7 days (1994); melting periods were 7 and pond) during snow-melt, but White-
days (1993) and 3 days (1994), and periods fronted Geese used them more often than did
after snow melt [end of melting to onset of Canada Geese.
incubation (median laying date + 4 days)] Pairwise compaiison tests showed that in
were 9 days (1993) and 13 days (1994). The both years Canada Geese used hummock and
total length of the preincubation periods on mud-flat habitats significantly more often than
the nesting ground were thus 26 d in 1993 and White-fronted Geese and that White-fronted
23 d in 1994. Geese used wet habitats significantly more of-
Geese were present along the river (on site ten than Canada Geese (Fig. 4C, D).
A or outside the intensive study area) upon Similar interspecific differences in habitat
our aiTival in 1993 {n = 50-80 pairs) and use were observed after snow melt in both
= =
1994 {n 140-150 pairs), but major anivals years (G-test of independence: 1993: G^^j
occuned aiound 27 May 993 and on or prior 23.03, P < 0.001; 1994 sites pooled: G =
1
to 20 May 1994 (see transect surveys: Fig. 3, 69.44, P < 0.001). Pairwise comparison tests
site A). During snow melt, goose numbers de- showed that White-fronted Geese used ponds
creased on site A (and from other areas along (1993 and 1994) and pond margins (1994)
the river) and increased slightly on site B as significantly more often than Canada Geese
geese dispersed from areas along the river to (Fig. 4E, F, G).
the rest of the study area (Figs. 1, 3). In 1993, habitat selection (i.e., use vs avail-
We are confident that the pairs observed ability) by both species differed after snow
=
during this study were part of the locally nest- melt (x" Goodness-of-fit: Canada Goose: x^
ing population because about Vi of the collared 94.8, P < 0.001; White-fronted Goose: yf =
individuals we found nesting in the study area 117.9, P < 0.001). Canada Geese preferred
{n > 1 1 of each species per year) were ob- (i.e., use > available) mud-flat, pond margin,
served on site A and other areas along the and pond, and avoided hummock habitats
river. Individuals collared in other study areas (Fig. 4E). White-fronted Geese preferred pond
were never observed on Walker Bay Study and avoided hummock habitat (Eig. 4E). In
Area (R.G.B., pers. obs.). 1994, most geese fed neai' tower 1 after snow
The first nests were found on 5 June 1993 melt (Fig. 1), where the relative availability of
and on 28 May 1994. Median laying dates habitats differed greatly between site A and B
were 11 June 1993 (White-fronted Goose: n (Fig. 4). Consequently, we analyzed habitat
= 38, Canada Goose: /r = 35) and 2 June use in each site separately. Data in dry (mud-
=
1994 (White-fronted Goose: n 26, Canada flat/hummock) and wet (pond maigin/pond)
Goose: n = 21) for both species (Kruskal- habitats were pooled at site B to obtain suf-
Wallis ANOVA on Ranks: H = 77.4, P < ficient sample sizes for x^ tests. Neai' the river
0.001; medians were different between years (site A), Canada Geese used habitats accord-
only; Fig. 3). The minimum intervals between ing to their availability (x' Goodness-of-fit: x"
goose arrival and median laying date were 14 = 0.92, P > 0.05; Fig. 4F), while White-front-
days in 1993 and 13 days in 1994. — ed Geese prefeired pond maigin and pond
=
Use and selection of habitats. White- habitats and avoided mud-flat habitats (x“
fronted and Canada geese did not differ in 49.8, P < 0.001). On site B, Canada Geese
their use of habitats before snow melt in either again used habitats according to their avail-
year (G-tests of independence: 1993: G.,jj = ability (x^ = 0.22, P > 0.05; Fig. 4G) and
0.083, 1 df, F > 0.05; 1994: G,„ = 0.031, 1 White-fronted Geese still prefeired wet habi-
df, P > 0.05; Fig. 4A, B). Both species also tats (pond margin/pond) and avoided dry ones
used habitats according to their availability (mud-fl—at/hummock; x‘ = 23.4, P < 0.001).
during that period (y^ Goodness-of-fit: all Diet. Nine food types were recognized in
< 3.08, P > 0.05). feces (Table 1 ). The number of different food
Habitat use differed between species during types detected increased as snow melted, as
snow melt in both years (G-tests of indepen- expected because of the increase in available
dence: 1993: G,jj = 18.14, P < 0.001; 1994: habitats. A major food before snow melt was
Gajj = 39.26, P < 0.001). Both species fed in Puccinellia spp. tillers, which accounted for
newly available wet habitats (pond margin 52% and 73% of White-fronted and Canada
174 THE WILSON BULLETIN • Vol. HI, No. 2, June 1999
1993 1994
Mud Hummock Mud Hummock
>s
B
ro
C>D
CD
TD
C
(D
0)
(D0
ro 100
B
XCD
Mud Hummock Margin Pond Mud Hummock Margin Pond
Canada Geese
I I
HEl White-fronted Geese
Availability(expected use)
Mud/Hummock Margin/Pond
FIG. 4. Use (% of feeding pairs) of mud-flat, hummock, pond margin, and pond habitats by White-fronted
(WE) and Canada geese (CG), and availability of these habitats during preincubation on the Walker Bay Study
WArEe;a,nN=WT3,83)1.99(3c--1d)99D4u.ri(an-gb)snBoewformeeltsn1o9w93me(lCtG:19n93=(C5G32:;nW=F:33n2;=W1E3:7)na=nd22189)94an(dCG1:99n4=(C6G3:7;/;W=E:12n65=;
=1688)7;).ha(bfi-tga)t Aafvtaielrabsinliotwy cmoeultldinnot199b4e,essittiemaAted(,CG(:e)nAf=ter50s;nWoFw;menlt=at33s)iteanAd isnite19B93(C(GC;G:n/;==22;120W;F:WFn; =n
29). A -I- indicates use > availability, indicates use < availability and no symbol indicates use =
>
availability (P 0.05).
goose diet respectively. After snow melt, more Stellaria humifusa, Diipontiafisheri, and Carex
than 50% of the diets of White-fronted and seeds could be underestimated (see methods,
Canada geese were composed of Carex spp. Cairiere 1996). Young leaves and open buds
and Diipontia fisheri. For both species, most of Salix spp. were found only in female Can-
(85%) feces contained food plants represen- ada Geese collected during incubation.
—
tative of at least 2 habitats. Consequently, Available biomass Plant biomass varied
.
changes in diet reflected changes in both hab- among combinations of habitats and sampling
itat use and food use within habitats. dates for both above ground (Kruskal-Wallis
The greater diversity of the diet found in ANOVA on ranks: 1993; H = 46.0, P <
the feces of Canada Geese relative to esophagi 0.001; 1994: H = 152.1, P < 0.001) and be-
(Table 1 ) is probably caused by the accumu- low ground plant parts (1993: H = 25.7, P =
lation of food fragments in the digestive sys- 0.012; 1994: H = 58.7, P < 0.001; Fig. 5).
tem. Nevertheless, analyses of esophageal There was little seasonal increase in total dry
content indicated that some Gramineae (frag- biomass within each habitat, except after the
ments not identified at the genus level) could median laying date lor above ground biomass
be overestimated in fecal analyses, whereas in pond margins (1994 only) and below
Carriere et al. • SPRING FEEDING BY ARCTIC GEESE 175
EIG. 6. Relationship between below ground bio-
mass available and proportion of feeding time spent
grubbing by female White-fronted (WE) and Canada
geese (CG) during preincubation on the Walker Bay
21 28 'June 6 14 Study Area, NWT, 1993-1994. Each point is the pro-
MUD-FLAT HUMMOCK MARGIN POND portion of scanned pairs observed grubbing (arcsine
square-root transformed) in a habitat during a specific
FIG. 5. Live above and below ground dry biomass period and year. Closed symbols are Canada Geese,
(mean ± SE) available to geese in 4 habitats during open symbols are White-fronted Geese. Habitats are
preincubation on the Walker Bay Study Area, NWT, mud-flat (circles), hummock (squares), pond margin
1993-1994. Values with same letter within graphs do (triangles), and pond (diamonds). Linear regressions:
not significantly differ (multiple comparison tests after for WE: y = 0.78 -F 0.91x [0.50-1.32; 6(95%C1)], F
a Kruskall-Wallis ANOVA on Ranks test foreach year, = 18.0, P = 0.001; for CG: y = 0.28 + 0.72x [0.27-
above and below ground biomass tested separately, all 1.17; B(95%CI)], F = 9.9, P = 0.009.
tests P < 0.02). Grey areas indicate periods of snow
melt (80-20% snow cover on site A). Number ofsam-
pled 20 X 20 cm quadrats per sampling date were: between years {F — 1.53, P > 0.05; habitat-
(1993) mud-flat = 3, 5, 17, 14; hummock = 6, 9, 11, year interaction, F = 4.09, P = 0.00—7).
1 1; pond margin = NA, 3, 6, 6; pond = NA, NA, 3, Use ofbelow ground food plants. Canada
2160,a1n6d, (1169,941)6;mupdo-nfdlamtar=gi1n2,=16N,A2,4, 1273,; 1h6u,m1m6;ocpkon=d Goose pairs grubbed less often than White-
= NA, NA, 16, 20. NA = datum was not available, fronted Geese (Canada Goose: 12.4%, White-
—
under snow. fronted Goose: 56.9%; Paired f-test: t
— 14.2, P < 0.001; Fig. 6), which grubbed ex-
tensively even in habitats where below-ground
biomass was very low (i.e., in mud-flat/hum-
ground biomass in pond margins (1993) and mock), before widespread snow melt and
pond (1994). Seasonal changes in below thawing of the ground surface. Spatial distri-
ground biomass were mostly the result of a bution of below ground vegetation (mostly
We
gradual deepening of the active layer. Elymus sp. rhizomes) was clumped in these
pooled sampling dates and found differences habitats and available below ground biomass
in above ground biomass among habitats may have effectively been much higher in
(Two Way ANOVA: F = 1 12.1, P < 0.001) some patches used by foraging individuals. In
and years (F = 4.25, P = 0.04; habitat-year all habitats, before and during snow melt,
interaction, F = 7.25, P < 0.001). Above most of the below ground biomass was frozen
ground biomass in pond margins was higher under the active layer and hence was not
than in any other habitat, particularly in 1994. available to geese.
We found a tendency for below ground bio- There was a significant positive relationship
mass to be lower in dry (0-1.08 g/m^) than in between the proportion of below ground bio-
wet habitats (1.33-24.4 g/m-; Two Way AN- mass in different habitat-year-period combi-
OVA: F = 2.61, P = 0.05), but no difference nations and the proportion of feeding time