Trumpeter swan behaviour at spring-migration stopover areas in southern Alberta

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1 2036 Trumpeter swan behaviour at spring-migration stopover areas in southern Alberta Jalene M. LaMontagne, Robert M.R. Barclay, and Leland J. Jackson Abstract: The use of breeding and wintering areas has been a focus of studies on trumpeter swans (Cygnus buccinator), but the importance of migration stopover areas has been overlooked. We conducted a behavioural study to assess trumpeter swans use of spring-migration stopover areas in southern Alberta, Canada. Adult swans foraged for 48% of the day, preened for 12%, rested for 26%, and were involved in locomotion for 14% of the time. Cygnets foraged for 49% of the day, preened for 15%, rested for 19%, and were involved in locomotion for 18% of their time. Temperature had a significant effect on the time budget of trumpeter swans: below 4 C, foraging diminished and sleeping was the dominant activity. The dominant activity of trumpeter swans in spring-migration stopover areas was foraging. We therefore suggest that these stopover areas are important for building the energy reserves required for successful migration and breeding. Résumé : L utilisation des aires de reproduction et des zones d hivernage par le Cygne trompette (Cygnus buccinator) a fait l objet de plusieurs études, mais l importance des aires de repos au cours de la migration n a jamais été déterminée. Nous avons procédé à une étude comportementale afin d évaluer l utilisation des aires de repos par le Cygne trompette pendant sa migration de printemps, dans le sud de l Alberta, Canada. Les cygnes adultes consacrent 48 % de leur journée à la quête de nourriture, 12 % au toilettage, 26 % au repos et ils sont en mouvement 14 % de leur temps. Les juvéniles cherchent leur nourriture pendant 49 % de leur journée, font du toilettage pendant 15 % et se reposent pendant 19 et 18 % de leur temps passe à la locomotion. La température a une influence considérable sur le bilan des activités; en dessous de 4 C, la quête de nourriture diminue et le sommeil devient la principale activité. L activité dominante dans les zones de repos pendant la migration est la quête de nourriture. Nous croyons que les aires de repos utilisées au cours de la migration permettent aux cygnes de se faire des réserves énergétiques en vue du succès de la migration et de la reproduction. [Traduit par la Rédaction] 2042 Introduction Many waterfowl gather energy reserves for continued migration and reproduction while at spring-migration stopover areas (Krapu 1981; LaGrange and Dinsmore 1988; Alisauskas and Ankney 1992). A positive relationship exists between reproductive output and energy-, protein-, and nutrient-reserve status upon arrival at breeding areas (Ankney and MacInnes 1978; Raveling 1979; Krapu 1981; Gammonley and Heitmeyer 1990). Studies that document the pattern of energy gain by waterfowl thus help to identify habitats that enhance the reproductive output of waterfowl (LaGrange and Dinsmore Received April 18, Accepted September 7, Published on the NRC Research Press Web site at on November 9, J.M. LaMontagne, 1,2 R.M.R. Barclay, and L.J. Jackson. Ecology Division, Department of Biological Sciences, University of Calgary, 2500 University Drive N.W., Calgary, AB T2N 1N4, Canada. 1 Corresponding author ( jalene.lamontagne@ualberta.ca). 2 Present address: Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. 3 R.H. Mackay Status report on Trumpeter Swan (Olor buccinator) in Canada. In Status reports on endangered wildlife in Canada. Vol. 1. Committee on the Status of Endangered Wildlife in Canada, Canadian Wildlife Service, Ottawa, Ont. (unpublished). LaMontagne et al. 1988). Investigators traditionally sample individuals, thereby removing them from the population (e.g., Raveling 1979; Krapu 1981; LaGrange and Dinsmore 1988). Trumpeter swans (Cygnus buccinator) were once reduced in number and classified as endangered (Mackay ), but since the middle of the twentieth century their numbers have increased. Although the biology of trumpeter swans in their wintering and breeding areas has been investigated (Shea 1979; Holton 1982; Maj 1983; Squires 1991), little is known of their biology during spring migration. During spring, most trumpeter swans in the Rocky Mountain Population migrate ~1400 km from overwintering areas in Montana, Idaho, and Wyoming (Tri-State area) through southern Alberta to breeding grounds in Grande Prairie, Alberta, or the Yukon (Mackay ). Observations of neckbanded birds suggest that many swans use the same ponds in discrete stopover areas year after year (G. Beyersbergen, personal communication). Trumpeter swans typically arrive at breeding lakes 2 3 weeks prior to thaw (Shandruk 1991). Nesting occurs as soon as nesting sites become ice-free (Pinel et al. 1991), and trumpeter swans have a high incubation constancy (Banko 1960; Mitchell 1994). Therefore, individuals likely arrive at breeding areas with endogenous energy reserves that are used during the reproductive period. Where trumpeter swans gain these energy reserves has not been identified. Body condition of trumpeter swans has not been thoroughly assessed because biologists have been reluctant to Can. J. Zool. 79: (2001) DOI: /cjz

2 LaMontagne et al use removal sampling (Weaver 1990; Krapu and Reinecke 1992). To identify important habitats, an alternative nondestructive technique is time-budget analysis (Grant et al. 1997). This technique allows key habitats to be identified, and their role in providing energy reserves can be established by comparing time budgets in different areas (i.e., migrationstopover habitats versus wintering or breeding habitats). The goals of our study were thus to document the behaviours of adult and cygnet trumpeter swans during spring migration in southern Alberta and to investigate the influence of ageclass (cygnets versus older swans) and external factors (ambient temperature, time of day) on time-budget allocation. If trumpeter swans use stopover areas to gain energy reserves for migration and breeding, an examination of their time budgets should demonstrate this. We hypothesized that foraging would be the dominant activity in stopover areas and that adults would forage more than cygnets to gain the additional energy reserves required for breeding. Methods Study area We studied trumpeter swan behaviour at two locations in Alberta, one approximately 50 km west of Calgary (51 05 N, W to N, W) and the other in the Cardston Mountain View area (49 02 N, W and N, W to W). These areas were identified as traditional stopover areas for trumpeter swans during spring migration, and are separated by approximately 250 km on the flyway (G. Beyersbergen, personal communication; D. Brown, personal communication). Both areas are located in the foothills of the Rocky Mountains; ranching is the main land use. West of Calgary we studied 13 ponds that ranged in size from 0.6 to 9.2 ha and had areas <1 m deep (and therefore available to foraging trumpeter swans; Scott 1972) that were between 0.3 and 4.1 ha (LaMontagne 2000). In the Cardston Mountain View area we focused on six ponds that varied in size from 0.4 to 18.2 ha, with areas <1 m deep ranging in size from 0.4 to 17.6 ha. The dominant macrophyte species in the study ponds were Potamogeton pectinatus, P. richardsonii, P. zosteriformis, Chara spp., Myriophyllum exalbescens, and Utricularia vulgaris (LaMontagne 2000). Cygnets and older swans were found on all ponds where swans occurred. We identified cygnets by their grey plumage, whereas older swans, which included both adults and subadults, had white plumage. Habitat use and time budgets We conducted daily counts and diurnal observations of trumpeter swans in the Calgary area from 7 April to 21 May 1999 (referred to as Calgary in 1999) and from 12 April to 11 May 2000 (Calgary in 2000). In the Cardston Mountain View area we made weekly counts from 4 March to 27 March 2000 and daily counts from 29 March to 11 April 2000 (Cardston Mountain View in 2000). We used focal-animal techniques (Martin and Bateson 1986) to quantify behaviours of 10 randomly selected individuals from each pond each day if swans were present. If fewer than 10 swans were present, all were observed. We did not discriminate between cygnets and adults while randomly selecting individuals for observation, but we did record age-class (cygnet or adult) for each observation. In trumpeter swans, no distinction between the sexes can be made at a distance, therefore we did not record sex differences. Each observation lasted 10 min. Individuals on a pond did not synchronize their behaviours, therefore we assumed that observations were independent for statistical purposes. We discarded observations of individuals that disappeared from view during the 10-min observation because of the possibility of bias (Baldassarre et al. 1988). We used binoculars and spotting telescopes to observe trumpeter swans from a distance of m. We checked all study ponds for the presence of trumpeter swans and conducted observations each day for the entire period when swans were present for Calgary in 1999 and for Cardston Mountain View ponds in In 2000, observations in the Calgary area began approximately 5 days after the first trumpeter swans arrived. With a stopwatch we timed the total duration of activities from 10-min focal-animal observations. We defined the activities as follows: locomotion (swimming, walking on ice or shoreline, flying), sleeping (head curled onto back or tucked under wing), head-up (either alert or relaxed), preening, and foraging. We also recorded the number of times foraging swans used tip-ups and rocking. Rocking was defined as a side-to-side motion associated with paddling the feet to expose food (Grant et al. 1997). Flying was recorded only when a swan flew from the study pond and returned during the 10-min observation or remained in sight during the whole observation. We also recorded the time (Mountain Standard Time) that each observation session began and the ambient temperature. To contrast cygnet and adult foraging behaviour we examined foraging bouts of 40 individuals (13 cygnets, 27 adults) at Calgary in We recorded the total duration of foraging (maximum of 15 tip-ups) and the duration of submergence for each tip-up in the foraging bout. Data analysis Prior to multivariate analysis (SYSTAT, version 7.0), we replaced values of 0 with We then ln-ratio-transformed the raw behavioural data (ratio of time spent in one behaviour to time spent in another behaviour), a standard procedure for compositional data analysis (Aitchison 1986; Aebischer et al. 1993). We did this to make the analyses more robust to problems associated with the lack of independence of dependent variables within a single observation, which violates assumptions of most statistical tests (Aebischer et al. 1993). This violation occurs in our data because the proportion of time an individual allocates to one behaviour is linked to the proportions spent in the other behaviours. Conducting a ln-ratio transformation of the data makes the ln-ratio variables independent, and statistical tests can then be applied (Aitchison 1986). Positive ln-ratio values indicate that the value of the numerator is greater than that of the denominator, while negative values are the opposite. The data did not follow a normal distribution (Kolmogorov Smirnov test, P < 0.05) and this could not be rectified with the arcsine transformation typically applied to behavioural data (Zar 1984). However, multivariate tests are robust against the assumption of normality provided the sample is large. We used Pillai s trace, as it is the most robust against violations of assumptions (Olson 1974; Lindman 1992). To analyse behaviours we combined sleeping and head-up into a single category ( rest ). We conducted multivariate analysis of variance (MANOVA) on ln-ratio-transformed behaviour data to determine variables that significantly influence trumpeter swan behaviour, with age-class (cygnet or adult), site (Calgary in 1999, Cardston Mountain View in 2000, Calgary in 2000), and the interaction of age-class and site as independent variables, and the ln-ratio-transformed behaviours as dependent variables. We used the three year-location combinations ( sites ) to control for withinyear (between stopover sites) and between-year variation in trumpeter swan behaviour. We conducted univariate tests when the MANOVA returned a significant result and we completed multiplecomparison tests on significant univariate tests. We compared the foraging behaviour of cygnets and adults (e.g., rate of tip-ups and rocking) by means of Mann Whitney U tests.

3 2038 Can. J. Zool. Vol. 79, 2001 Table 1. Proportions of time spent in various activities by adult and cygnet trumpeter swans in Calgary in 1999, Cardston Mountain View in 2000, and Calgary in Activity Calgary 1999 Cardston Mountain View 2000 Calgary 2000 Adults (n = 409) Cygnets (n = 133) Adults (n = 158) Cygnets (n = 33) Table 2. Univariate test statistics for ln-ratio behaviours included in a MANOVA. Adults (n = 431) Age effect Site effect Age site effect Ln-ratio behaviour df F P F P F P Foraging/preening 2, Foraging/resting 2, < Foraging/locomotion 2, < Locomotion/preening 2, Locomotion/resting 2, Preening/resting 2, < Cygnets (n = 174) Foraging (0.021) (0.035) (0.033) (0.073) (0.021) (0.032) Preening (0.012) (0.023) (0.016) (0.057) (0.011) (0.020) Head-up a (0.004) (0.007) (0.005) (0.005) (0.005) (0.007) Sleeping a (0.017) (0.020) (0.031) (0.059) (0.019) (0.029) Flying/walking b (0.001) (0.000) (0.006) (0.010) (0.002) (0.002) Swimming b (0.010) (0.021) (0.014) (0.031) (0.011) (0.020) Note: Values are given as the mean, with SE in parentheses. Sample sizes are the number of 10-min observations completed on individual swans. a Combined into a single category, rest, for data analysis. b Combined into a single category, locomotion, for data analysis. We used Spearman s rank correlation to determine the influence of ambient temperature on the proportion of time allocated to foraging and sleeping, the dominant behaviours. We did not differentiate between age-classes or sites for correlation analysis. We calculated an average value for foraging and sleeping at each temperature and conducted the correlation on the average values. We also compared the average daily minimum temperatures in April 1999 and 2000 for the Calgary area to assess whether conditions differed between years. We examined time-of-day effects on proportions of time allocated to different activities using five time intervals: early morning (05:00 07:59), late morning (08:00 10:59), early afternoon (11:00 13:59), late afternoon (14:00 16:59), and evening (17:00 19:59). We combined all sites for this analysis, although we conducted separate analyses for adults and cygnets using a Kruskal Wallis test for each behaviour. We conducted nonparametric pairwise comparisons on significant results (Siegel and Castellan 1988). Means and standard errors are reported throughout, and a 0.05 probability level was used to determine significance. Results In both study areas swans spent more time foraging than any other activity, and flew/walked the least (Table 1). The proportion of time spent foraging was greater in Calgary in 1999 than at either location in 2000, whereas the proportion of time spent sleeping/head-up was greater in 2000 than in The overall activity budgets were similar for adults and cygnets in Cardston Mountain View in 2000 and Calgary in Our results derive from 1338 behavioural observations conducted over h. We conducted 542 ten-min observations (409 adults and 133 cygnets) at the Calgary 1999 site, 605 observations (431 adults and 174 cygnets) at Calgary in 2000, and 191 observations (158 adults and 33 cygnets) at Cardston Mountain View in Age of the swans significantly influenced the proportion of time allocated to behaviours (Pillai s trace = 0.061, df = 12 and 2656, P < 0.001), as did site (Pillai s trace = 0.011, df = 12 and 2656, P < 0.05) and age site (Pillai s trace = 0.018, df = 12 and 2656, P < 0.05). Age-class explained a significant component of the variation in ln(preen/rest) (Tables 2 and 3), as cygnets at Cardston Mountain View preened significantly more and rested significantly less than adults (Table 1). There was no significant difference between adults and cygnets for any behaviours that included foraging (Table 2). There was a site (year-location) effect for all behaviours (Table 2). Generally, behaviours at Cardston Mountain View in 2000 and Calgary in 2000 were not significantly different, while behaviours in Calgary in 1999 were significantly different from 2000 data (Table 3). As no significant difference was detected in the time allocated to foraging by adults versus cygnets, we examined foraging in more detail in Calgary ponds in 2000 to determine whether there were differences in the way adults and cygnets foraged. There was no significant difference in the tip-up rates of adults (3.41 ± 0.04/min) from those of cygnets (3.35 ± 0.07/min; U = 77389, n = 638 and 233, P > 0.05), nor in the average time spent submerged during a tip-up (12.61 ± 0.34 s for adults and ± 0.46 s for cygnets; U = , n = 323 and 156, P > 0.05). The proportion of foraging time spent submerged also did not differ significantly between adults (0.70 ± 0.03) and cygnets (0.73 ± 0.03; U = 149, n = 27 and 13, P > 0.05). However, adults had a significantly higher rate of rocking (0.86 ± 0.03/min) than cygnets (0.68 ± 0.05/min; U = 84451, n = 638 and 233, P < 0.005). This difference was also evident in the proportion of time during which tip-ups were preceded by rocking. Adults rocked before ± of their tip-ups, while

4 LaMontagne et al Fig. 1. Influence of ambient temperature on the proportion of time trumpeter swans spent foraging (A) and sleeping (B). Each point represents the average proportion of time the behaviour occurred at each temperature. 1.0 (A) 1.0 (B) Proportion of time Proportion of time Ambient temperature ( C) Ambient temperature ( C) Table 3. Tukey s post hoc comparisons of ln-ratio behaviour values included in the MANOVA following significant univariate tests. Adults Ln-ratio behaviour Calgary 1999 Cygnets Cardston Mountain View 2000 Calgary 2000 Calgary 1999 Cardston Mountain View 2000 Calgary 2000 Foraging/preening 3.24 (0.47)a 2.66 (0.74)b 2.57 (0.45)b 4.17 (0.81)a 0.65 (1.91)b 2.84 (0.73)b Foraging/resting 4.96 (0.56)a 1.47 (0.90)b 1.31 (0.56)b 7.20 (0.81)a 1.79 (2.02)b 2.53 (0.87)b Foraging/locomotion 2.61 (0.37)a 1.40 (0.52)b 1.15 (0.34)b 3.92 (0.67)a 1.24 (0.87)b 0.11 (0.51)b Locomotion/preening 0.64 (0.37)ab 1.26 (0.58)ab 1.33 (0.36)ab 0.25 (0.62)ab 1.89 (1.57)a 2.52 (0.55)b Locomotion/resting 2.34 (0.45)a 0.07 (0.73)b 0.11 (0.47)b 3.28 (0.69)a 0.55 (1.74)b 2.05 (0.74)b Preening/resting 1.71 (0.37)a 1.19 (0.54)b 1.21 (0.38)b 3.03 (0.59)a 2.44 (1.09)ab 0.23 (0.57)b Note: Values are given as the mean, with SE in parentheses. Values followed by the same letter across site and age-class are statistically similar (P > 0.05). cygnets rocked before ± of their tip-ups (U = 83792, n = 638 and 233, P < 0.005). Ambient temperature had a significant effect on the proportion of time trumpeter swans allocated to foraging (r = 0.268, n = 30, P < 0.05) and sleeping (r = 0.331, n = 30, P < 0.05), the two major activities. Trumpeter swans restricted their activities at lower temperatures (below 4 C); sleeping was the dominant activity and foraging levels decreased (Fig. 1). At temperatures higher than 4 C, trumpeter swans allocated ~55% of their time to foraging, while the proportion of time allocated to sleeping decreased rapidly and remained low (0 20%) with further increases in temperature. The average daily minimum temperatures in April 2000 ( 3.9 ± 1.1 C) were significantly lower (T = 1.69, df = 23, P = 0.05) than in April 1999 ( 1.8 ± 1.0 C). In 1999 the lowest daily minimum temperature was 13 C, while on the coldest day in 2000 the temperature was 17 C. Time of day significantly affected the proportion of time adults allocated to preening (T = 20.26, n = 999, P < 0.001) and locomotion (T = 20.85, n = 999, P < 0.001) but not foraging (T = 8.34, n = 999, P > 0.05) or resting (T = 7.59, n = 999, P > 0.05). Preening was least common in the morning, with higher levels during late afternoon. The proportion of time adults spent in locomotor activities was almost uniform throughout the day, but increased into the evening, although no significant difference was detected with pairwise comparisons. Foraging remained high throughout the day, while resting was highest from early morning to early afternoon and decreased into the evening (Fig. 2). The proportion of time cygnets foraged was the only behaviour significantly affected by time of day (T = 10.35, n = 339, P < 0.05). Cygnets fed most from early morning to early afternoon (Fig. 2). Discussion It has been postulated that trumpeter swans derive a significant proportion of the energy required for breeding from

5 2040 Can. J. Zool. Vol. 79, 2001 Fig. 2. Proportions of time (mean ± SE) allocated by adults (A) and cygnets (B) to foraging, preening, resting, and locomotion, according to time-of-day interval: early morning (05:00 07:59), late morning (08:00 10:59), early afternoon (11:00 13:59), late afternoon (14:00 16:59), and evening (17:00 19:59). Values with the same letter do not differ significantly in proportion of time allocated to a behaviour between time-of-day intervals according to multiple-comparison tests. 0.6 (A) 0.6 a ac a (B) c Proportion of time b Proportion of time b 0.1 a a ab ab :00-07:59 08:00-10:59 11:00-13:59 Time of day 14:00-16:59 17:00-19: :00-07:59 08:00-10:59 11:00-13:59 Time of day 14:00-16:59 17:00-19:59 Foraging Preening Resting Locomotion wintering grounds and (or) spring-migration stopover areas (Krapu and Reinecke 1992). However, this hypothesis remains untested because biologists are reluctant to harvest trumpeter swans to assess body condition (Weaver 1990), therefore the only viable method for determining where trumpeter swans gather energy reserves is time-budget studies (Grant et al. 1997). Trumpeter swans migrating through southern Alberta allocated the greatest proportion of their time to foraging while at the two stopover areas we examined. The average proportion of time spent foraging (0.486 ± 0.012) was much higher than that reported for wintering areas (0.296 ± 0.027; Squires and Anderson 1997) but similar to the proportion recorded for nonmigratory individuals of the Rocky Mountain population in spring (0.445 ± 0.021) (Squires and Anderson 1997). The proportions of time allocated to the other primary behaviours (swimming, preening, sleeping) by our migratory subpopulation and the nonmigratory subpopulation were similar (Squires and Anderson 1997). The dominance of foraging in the spring time budgets of migratory and nonmigratory trumpeter swans compared with winter activity indicates that swans likely build up energy reserves before breeding. Trumpeter swans in the Canadian subpopulation take up to 2 months to complete their relatively short migration of ~1400 km, which allows considerable time for foraging (Mackay ; Mitchell 1994). This suggests that stopover sites are rich in food (Shea 1979) and are energetically profitable stops and (or) that swans must stay longer to recoup energy reserves lost while flying between stopover areas. Some other species of migrating waterfowl display similar behavioural patterns (Paulus 1988). Trumpeter swans arrive at breeding lakes to reclaim previous territories prior to ice-out (Banko 1960; Shandruk 1991; Mitchell 1994), and breeding activities begin as soon as nesting sites become ice-free in late April or early May (Pinel et al. 1991; Squires 1991). Therefore, little opportunity exists at breeding areas for individuals to gather the reserves required to lay eggs (Holton 1982; Maj 1983). During the incubation period (32 34 days), females spend 95 96% of their day on the nest (Cooper 1979; Holton 1982), and high incubation constancy is important for reproductive success (Shea 1979; Squires 1991). Therefore, female swans essentially fast during the incubation period and must rely on endogenous energy reserves for survival (Bacon and Anderson- Harild 1989). Although male trumpeter swans do not incubate the eggs (Holton 1982), they are active in territorial defence and nest maintenance (Shea 1979; Henson and Cooper 1992). Foraging levels of females and males increase after eggs hatch (Squires 1991). The high spring foraging effort we observed is consistent

6 LaMontagne et al with the hypothesis that spring-migration stopover areas provide important reserves required for migration and subsequent breeding, as observed in some species of arctic-nesting geese (Ankney and MacInnis 1978; Raveling 1979; McLandress and Raveling 1981). These patterns are in contrast to those of trumpeter swans of the Pacific population that breed in Alaska and have the opportunity to exploit local resources during the prenesting and incubation periods (Grant et al. 1994). Little is known of the migration patterns and time budgets of trumpeter swans en route to Alaskan breeding grounds. Breeding adult swans might be expected to forage more than cygnets because of greater energy and nutrient requirements, yet the proportions of time allocated to foraging did not differ significantly. This was also found during winter and spring for Tri-State trumpeter swans (Squires 1991). Over-winter mortality is higher for cygnets than for adults (R. Shea, personal communication), and surviving cygnets may leave wintering areas in poorer condition than adults. Therefore, cygnets may need to allocate a large proportion of their time to foraging at spring-migration stopover areas. Because trumpeter swans typically begin breeding at 5 years of age (Brechtel 1982) but gain white feathers after their second summer (Mitchell 1994), we could not distinguish nonbreeding subadults from breeding adults. This may have contributed to the lack of a significant difference in the behaviours of cygnets and adults. Adults exhibited a greater rate of rocking than cygnets, and rocked before tipping a greater proportion of the time. The foot action associated with rocking exposes and dislodges food items from the sediment (Hampton 1981). Therefore, although foraging times were similar, our results suggest that adults may be more efficient foragers than cygnets because of their experience, and hence have a higher net gain of energy (Woodrey and Moore 1997). Decreased foraging and increased sleeping are correlated with decreasing temperature (Squires and Anderson 1997), and air temperature affects trumpeter swan behaviour (Squires 1991; this study). Foraging activity of other waterfowl typically increases as temperature decreases to 0 C (Paulus 1988), but at lower temperatures, energetic costs may exceed benefits gained from foraging (Brodsky and Weatherhead 1984; Paulus 1988), and sleeping becomes the dominant activity (Squires 1991). In our study, foraging decreased at temperatures below 4 C. At temperatures above 4 C, foraging time was not related to temperature and sleeping was uncommon. This may explain the decrease in foraging and increase in resting in 2000, as the spring was colder than in The timing of activities and movement of waterfowl are typically cued by dawn and dusk (Paulus 1988). We observed minor variation in trumpeter swan behaviour during the day, but overall time budgets were not strongly influenced by time of day, as is also the case for nonmigratory trumpeter swans (Squires and Anderson 1997). Other studies showed that trumpeter swans are active throughout the night, with little deviation in their time budgets from during the day (Squires and Anderson 1997). Our results indicate that migrating trumpeter swans of all ages spend most of their time foraging while at stopover areas. As less time is spent foraging prior to migration (Squires and Anderson 1997) or when the birds arrive at breeding areas (Holton 1982), we suggest that ponds at migration stopover areas represent critical habitat that is key to successful migration and breeding. As the population of migrating trumpeter swans increases and reintroduction programs lead to the establishment of new populations (e.g., Beyersbergen and Kaye 2000; Gillette 2000), ensuring the availability of sufficient high-quality stopover habitat will remain essential. Acknowledgements We thank G. Beyersbergen, D. Brown, V. Romeril, and L. Hills for information used in selecting study ponds; C. Solohub, A. Dennis, C. Friedrich for fieldwork assistance; D. Lybbert and N. Copithorne for field support; and E. Crone, C. Chinnappa, C. Gates, D. Hill, and R. Shea for comments. We also thank the many landowners who permitted access to study ponds; Alberta Environmental Protection (Cardston office) and E. Crone for providing field housing; and E. Crone for giving valuable statistical advice. This study was supported financially by Natural Sciences and Engineering Research Council of Canada grants to R.M.R.B. and L.J.J., the Challenge Grants in Biodiversity Program, and a University of Calgary Thesis Research Grant to J.M.L. References Aebischer, N.J., Robertson, P.A., and Kenward, R.E Compositional analysis of habitat use from animal radio-tracking data. Ecology, 74: Aitchison, J The statistical analysis of compositional data. Chapman and Hall, London. Alisauskas, R.T., and Ankney, C.D The cost of egg laying and its relationship to nutrient reserves in waterfowl. In Ecology and management of breeding waterfowl. Edited by B.D.J. Batt, A.D. Afton, M.G. Anderson, C.D. Ankney, D.H. Johnson, J.A. Kadlec, and G.L. Krapu. University of Minnesota Press, Minneapolis. pp Ankney, C.D., and MacInnes, C.D Nutrient reserves and reproductive performance of female Lesser Snow Geese. Auk, 95: Bacon, P.J., and Anderson-Harild, P Mute swan. In Lifetime reproduction in birds. Edited by I. 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