Greater Snow Geese Research Articles

Scale-dependent effects of herbivory on moss communities in Arctic wetlands: A 25-year experiment.

Arctic ecosystems are undergoing rapid changes, including increasing disturbance by herbivore populations, which can affect plant species coexistence and community assemblages. Although the significance of mosses in Arctic wetlands is well recognized, the long-term influence of medium-sized herbivores on the composition of moss communities has received limited attention. We used data from a long-term (25 years) Greater Snow Goose (Anser caerulescens atlanticus) exclusion experiment in Arctic tundra wetlands to assess changes in the composition of moss communities at multiple spatial scales (cell, 4 cm2; quadrat, 100 cm2; exclosure, 16 m2). We investigated how snow goose grazing and grubbing can alter the composition of the moss community by measuring changes in alpha and beta diversity, as well as in the strength of plant interspecific interactions between moss species. Our results indicate that goose foraging significantly increased species diversity (richness, evenness, and inverse Simpson index) of moss communities at the cell and quadrat scales but not the exclosure scale. Goose foraging reduced the dissimilarity (beta diversity) of moss communities at all three scales, mainly due to decreased species turnover. Furthermore, goose foraging increased positive interaction between moss species pairs. These findings emphasize the critical role of geese in promoting moss species coexistence and increasing homogeneity in Arctic wetlands. This study illustrates how top-down regulation by herbivores can alter plant communities in Arctic wetlands and highlights the importance of considering herbivores when examining the response of Arctic plant biodiversity to future climate change.

Can arctic migrants adjust their phenology based on temperature encountered during the spring migration? The case of the greater snow goose

The reproductive phenology of many long-distance migrants breeding at high latitudes remains unresponsive or responds only slightly to climate warming. In order to adjust migration speed and arrival time on the breeding grounds, environmental cues encountered during the migration must be related to conditions prevailing at the breeding site. However, heterogeneity in rate of climate warming across latitudes may hamper the ability of birds to adjust their migration speed adequately. We examined to what extent temperatures encountered at stopovers were a good predictor of temperatures at subsequent stopovers and at the breeding site in greater snow geese (Anser caerulescens atlanticus), an Arctic species that showed little change in its breeding phenology over the past 3 decades. We also examined temperature trends at various stopovers used by geese and at the breeding site over a 40-year period. We found that warming was stronger at the Arctic stopovers and the breeding site than at southern staging areas. The mean temperature and rate of temperature change encountered at the southern stopover, where this species accumulates most of its body reserves, was weakly correlated to temperatures prevailing at more northern stopovers and the breeding site located 3,000 km further north. Correlations in temperatures between stopovers and the breeding site increased with decreasing distance between sites and as geese moved further north. Lastly, laying date was strongly related to temperature during the arrival and pre-laying period on the breeding grounds but not to temperatures encountered at stopovers during migration. Temperatures encountered along the migratory route are thus a poor predictor of temperatures prevailing at the breeding site in any given year except when geese are getting close to their breeding grounds. This may be a major constraint preventing geese from adjusting their migratory schedule to conditions on their breeding grounds and may explain why their reproductive phenology did not change despite a warming trend at the breeding site.

Morphological differences and migration patterns of greater and lesser snow geese in New York State

AbstractLesser (Chen caerulescens caerulescens, LSGO) and greater snow goose (Chen caerulescens atlantica, GSGO) populations have increased substantially in the past 50 years. The light goose conservation order established in 1998 (Canada) and 1999 (U.S.) aimed to increase snow goose harvest and stabilize populations because breeding ground abundance was thought to negatively impact arctic ecosystems. In the Atlantic flyway, where LSGO and GSGO are both available for harvest, techniques to differentiate sub‐species in the field using morphology may be helpful for harvest management because mid‐continent LSGO are ~16 times more abundant than GSGO (n < 1,000,000). We investigated percentages and spatial distribution of LSGO and GSGO in the spring harvest in NY as this information could be useful for snow goose population and harvest management decisions. We developed a discriminant function analysis (DFA) using heads from snow geese harvested during spring 2016 to 2018 and were able to differentiate between LSGO and GSGO with 95.5% accuracy. Based on the DFA results, we estimated that spring harvest in New York state was 80% GSGO and 20% LSGO. Using band recoveries from autumn and spring harvests, we also identified that GSGO harvest occurred farther west during spring than autumn and in the 2010s than prior two decades. Our results indicate that GSGO comprise most snow goose harvest in New York state and provide evidence for a shift in spring migration patterns of GSGO since the 1990s.

Evidence for synergistic cumulative impacts of marking and hunting in a wildlife species

Abstract Nonadditive effects from multiple interacting stressors can have unpredictable outcomes on wildlife. Stressors that initially have negligible impacts may become significant if they act in synergy with novel stressors. Wildlife markers can be a source of physiological stress for animals and are ubiquitous in ecological studies. Their potential impacts on vital rates may vary over time, particularly when changing environments impose new stressors. In this study, we evaluated the temporal changes in the combined impact of two stressors, one constant (collar marking) and another one variable over time (hunting intensity), in greater snow geese (Anser caerulescens atlantica). Over a 30‐year period (1990–2019), hunting regulations were liberalized twice, in 1999 and 2009, with the instauration of special spring and winter hunting seasons respectively. We evaluated the effect of collars on goose survival through this period of changing hunting regulations. We compared annual survival of >20,000 adult females marked with and without neck collars using multi‐event capture–recapture models, and partitioned hunting from nonhunting mortality. Survival of geese marked with or without collars was similar in 1990–1998, before hunting regulations were liberalized (average survival [95% CI]: 0.87 [0.86, 0.89]). However, absolute survival of collared geese was 0.05 [0.03, 0.07] lower than that of noncollared geese between 1999 and 2009, and 0.12 [0.09, 0.15] lower after hunting regulations were liberalized further in 2009. Hunting and nonhunting mortality probabilities were both higher in collared birds compared to those without collars. The interaction between the effects of collars and hunting was synergistic because collars affected survival only after the hunting pressure increased significantly. These cumulated stresses probably reduced goose body condition sufficiently to increase their vulnerability to multiple sources of mortality.

Digging into the behaviour of an active hunting predator: arctic fox prey caching events revealed by accelerometry

BackgroundBiologging now allows detailed recording of animal movement, thus informing behavioural ecology in ways unthinkable just a few years ago. In particular, combining GPS and accelerometry allows spatially explicit tracking of various behaviours, including predation events in large terrestrial mammalian predators. Specifically, identification of location clusters resulting from prey handling allows efficient location of killing events. For small predators with short prey handling times, however, identifying predation events through technology remains unresolved. We propose that a promising avenue emerges when specific foraging behaviours generate diagnostic acceleration patterns. One such example is the caching behaviour of the arctic fox (Vulpes lagopus), an active hunting predator strongly relying on food storage when living in proximity to bird colonies.MethodsWe equipped 16 Arctic foxes from Bylot Island (Nunavut, Canada) with GPS and accelerometers, yielding 23 fox-summers of movement data. Accelerometers recorded tri-axial acceleration at 50 Hz while we obtained a sample of simultaneous video recordings of fox behaviour. Multiple supervised machine learning algorithms were tested to classify accelerometry data into 4 behaviours: motionless, running, walking and digging, the latter being associated with food caching. Finally, we assessed the spatio-temporal concordance of fox digging and greater snow goose (Anser caerulescens antlanticus) nesting, to test the ecological relevance of our behavioural classification in a well-known study system dominated by top-down trophic interactions.ResultsThe random forest model yielded the best behavioural classification, with accuracies for each behaviour over 96%. Overall, arctic foxes spent 49% of the time motionless, 34% running, 9% walking, and 8% digging. The probability of digging increased with goose nest density and this result held during both goose egg incubation and brooding periods.ConclusionsAccelerometry combined with GPS allowed us to track across space and time a critical foraging behaviour from a small active hunting predator, informing on spatio-temporal distribution of predation risk in an Arctic vertebrate community. Our study opens new possibilities for assessing the foraging behaviour of terrestrial predators, a key step to disentangle the subtle mechanisms structuring many predator–prey interactions and trophic networks.

Eastern Canada Flocks: images and manually annotated bird positions.

The Eastern Canada (ECA) Flocks data set consists of manually annotated images from the Common Eider (COEI, Somateria mollissima) Winter Survey and the Greater Snow Geese (GSGO, Anser caerulescens atlanticus) Spring Survey. The images were taken in eastern Canada using fixed-wing aircraft and manually annotated with ImageJ's Cell counter plugins. We selected and annotated the ECA Flocks images in order to test the precision of the CountEm flock size estimation method. ECA Flocks includes 179 COEI and 99 GSGO single flock images. We cut each image manually to a rectangle that excluded large parts of the image with no birds. Both versions (original and cut) of each image are available in the data set. We manually annotated 637,555 (124,309 COEI and 514,235 GSGO) bird positions in the cut images from both surveys. Each bird has an associated "Type," which refers to species and/or sex. Sex identification was only possible for adult common eiders, because females and immature males are brown birds, whereas adult males have mainly white plumage. In the COEI images 64,484 males and 58,029 females, as well as 1,796 birds of other species, were identified. In the GSGO images 504,891 Snow Geese and 9,344 birds of other species were labeled. A .csv file including all annotated bird positions and types is available for each image. The COEI and GSGO photos of the ECA Flocks data set were taken in the years 2006 and 2018 and 2016-2018, respectively. We selected these photos in order to include images with different quality and resolution. COEI and GSGO flock sizes range from 6 to 4,154 and from 43 to 36,241 respectively. There is high variability in light conditions, backgrounds, and number and spatial arrangement of birds across the images. The data set is therefore potentially useful to test the precision of methods for analyzing imagery to estimate the abundance of animals by directly detecting, identifying, and counting individuals. We release these data into the public domain under a Creative Commons Zero license waiver. When you use the data in your publication, cite this data paper. Should ECA Flocks be a major part of the data analyzed in your study, you should consider inviting the ECA Flocks originators as collaborators. If you plan to use the ECA Flocks data set, we request that you contact the ECA Flocks core team to learn whether updates are available, and whether similar analyses are already ongoing.

Prey and habitat distribution are not enough to explain predator habitat selection: addressing intraspecific interactions, behavioural state and time

BackgroundMovements and habitat selection of predators shape ecological communities by determining the spatiotemporal distribution of predation risk. Although intraspecific interactions associated to territoriality and parental care are involved in predator habitat selection, few studies have addressed their effects simultaneously with those of prey and habitat distribution. Moreover, individuals require behavioural and temporal flexibility in their movement decisions to meet various motivations in a heterogeneous environment. To untangle the relative importance of ecological determinants of predator fine-scale habitat selection, we studied simultaneously several spatial, temporal, and behavioural predictors of habitat selection in territorial arctic foxes (Vulpes lagopus) living within a Greater snow goose (Anser caerulescens atlantica) colony during the reproductive season.MethodsUsing GPS locations collected at 4-min intervals and behavioural state classification (active and resting), we quantified how foxes modulate state-specific habitat selection in response to territory edges, den proximity, prey distribution, and habitats. We also assessed whether foxes varied their habitat selection in response to an important phenological transition marked by decreasing prey availability (goose egg hatching) and decreasing den dependency (emancipation of cubs).ResultsMultiple factors simultaneously played a key role in driving habitat selection, and their relative strength differed with respect to the behavioural state and study period. Foxes avoided territory edges, and reproductive individuals selected den proximity before the phenological transition. Higher goose nest density was selected when foxes were active but avoided when resting, and was less selected after egg hatching. Selection for tundra habitats also varied through the summer, but effects were not consistent.ConclusionsWe conclude that constraints imposed by intraspecific interactions can play, relative to prey distribution and habitat characteristics, an important role in the habitat selection of a keystone predator. Our results highlight the benefits of considering behavioural state and seasonal phenology when assessing the flexibility of predator habitat selection. Our findings indicate that considering intraspecific interactions is essential to understand predator space use, and suggest that using predator habitat selection to advance community ecology requires an explicit assessment of the social context in which movements occur.

Temporal changes in reproductive success and optimal breeding decisions in a long-distance migratory bird

Many avian migrants have not adjusted breeding phenology to climate warming resulting in negative consequences for their offspring. We studied seasonal changes in reproductive success of the greater snow goose (Anser caerulescens atlantica), a long-distance migrant. As the climate warms and plant phenology advances, the mismatch between the timing of gosling hatch and peak nutritive quality of plants will increase. We predicted that optimal laying date yielding highest reproductive success occurred earlier over time and that the seasonal decline in reproductive success increased. Over 25 years, reproductive success of early breeders increased by 42%, producing a steeper seasonal decline in reproductive success. The difference between the laying date producing highest reproductive success and the median laying date of the population increased, which suggests an increase in the selection pressure for that trait. Observed clutch size was lower than clutch size yielding the highest reproductive success for most laying dates. However, at the individual level, clutch size could still be optimal if the additional time required to acquire nutrients to lay extra eggs is compensated by a reduction in reproductive success due to a delayed laying date. Nonetheless, breeding phenology may not respond sufficiently to meet future environmental changes induced by warming temperatures.

Consequences of a changing environment on the breeding phenology and reproductive success components in a long‐distance migratory bird

AbstractMigratory birds have a narrow time window to breed, especially in the Arctic, where early nesting typically yields the highest reproductive success. We assessed temporal changes (1991–2015) in reproductive success components in relation to timing of breeding in greater snow geese (Chen caerulescens atlantica). This species breeds in the Canadian Arctic, a region that has experienced a strong warming trend. We tested the effect of laying or hatching date, year and their interaction on six reproductive components: Total clutch laid, nesting success, egg survival, hatching success, prefledging, and postfledging survival. Over 25 years, mean laying date changed little, even though it advanced 1.8 days in early breeders and was delayed 3 days in late breeders. Likewise, the number of eggs in nests initiated early in the season decreased by 0.6 egg, whereas in late nests it increased by 0.3 egg. Success of nests initiated early and late in the season was lower than nests initiated near the population mean, and consistently increased over time. The proportion of eggs surviving to partial predation and postfledging survival decreased with laying date but the pattern did not change over time. In contrast, prefledging survival was not affected by laying date initially but declined in nests initiated late in the season toward the end of the study. Overall, nests initiated close to the population mean showed little temporal change for most components of reproductive success and seem to be less affected by environmental change than nests initiated early and late in the season.

Direct and indirect effects of regional and local climatic factors on trophic interactions in the Arctic tundra

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

Picking the right cache: caching site selection for egg predators in the arctic

Food hoarding is often considered an adaptive behaviour to extend the period of availability of food resources. Finding the right caching site for storage and retrieval is of paramount importance, yet how caching sites are selected is poorly known. Here, we examine site selection for egg caching by a tundra predator, the arctic fox, Vulpes lagopus, which can overcome large seasonal prey variations by extensive caching. During the short arctic summer, colonial breeding birds like geese produce in a short time period many eggs, which provide a large quantity of predictable resources for consumption and caching. We predicted that foxes would select caching sites with specific characteristics, such as shallow permafrost, and tall hummocks (small mounds in tundra landscapes, which should facilitate caching and provide visual cues for subsequent retrieval). We sampled the main physical characteristics of 48 caches and paired random sites inside a Greater Snow Goose (Chen caerulescens) colony. Our study shows that foxes favour cache sites characterized by hummocks nearly twice as higher than at nearby random sites. The depth of the active layer of permafrost did not influence cache site selection. Foxes may select tundra features that possibly enhance caching efficiency and retrieval probability. Our study elucidates one aspect of food hoarding behaviour in extreme habitats characterized by strong variations of resource availability.

Identification of Type A Influenza Viruses from Wild Birds on the Delmarva Peninsula, 2007-10.

Wild waterfowl and shorebirds in the Delaware-Maryland-Virginia (Delmarva) Peninsula region within the Atlantic Flyway were sampled as part of the Early Detection of Highly Pathogenic H5N1 Avian Influenza (AI) in Wild Migratory Birds program. The U.S. Department of Agriculture (USDA) and state wildlife agencies submitted 7858 samples for AI virus (AIV) testing by real-time reverse transcription PCR (rRT-PCR) to the University of Delaware Poultry Health System from April 2007 to March 2011. Virus isolation attempts were performed on samples with matrix gene cycle threshold (Ct) values ≤33.9. Using rRT-PCR, AIV was detected in 14% (1091/7857) of the samples. In species with sample sizes >100, American black duck ( Anas rubripes ; 28%), ruddy turnstone ( Arenaria interpres ; 27%), American green-winged teal ( Anas crecca ; 21%), semipalmated sandpiper ( Calidris pusilla ; 27%), greater snow goose ( Chen caerulescens atlanticus; 12%), mallard ( Anas platyrhynchos ; 10%), and northern pintail ( Anas acuta ; 14%) showed the highest rates of AIV detection. Forty-two AIVs were recovered from eight species: American black duck, mallard, ruddy turnstone, American green-winged teal, greater snow goose, Canada goose ( Branta canadensis ), ring-necked duck ( Aythya collaris ), and mallard × American black duck ( Anas platyrhynchos × Anas rubripes ). Recovered H5 (n = 2) and H7 (n = 2) viruses were found to be low pathogenicity by the USDA National Veterinary Services Laboratory. Additional AIVs represented a diversity of subtype combinations: H1-H4, H6, and H10 and H11 and N subtypes N1-N9 and N6-N9. The rate of AIV recovery from swabbings was inversely related to Ct value, ranging from 50% for Ct values of 16.0-18.9 to 5.1% for Ct values of 31-33.9.

Partitioning prediction uncertainty in climate-dependent population models.

The science of complex systems is increasingly asked to forecast the consequences of climate change. As a result, scientists are now engaged in making predictions about an uncertain future, which entails the efficient communication of this uncertainty. Here we show the benefits of hierarchically decomposing the uncertainty in predicted changes in animal population size into its components due to structural uncertainty in climate scenarios (greenhouse gas emissions and global circulation models), structural uncertainty in the demographic model, climatic stochasticity, environmental stochasticity unexplained by climate-demographic trait relationships, and sampling variance in demographic parameter estimates. We quantify components of uncertainty surrounding the future abundance of a migratory bird, the greater snow goose (Chen caeruslescens atlantica), using a process-based demographic model covering their full annual cycle. Our model predicts a slow population increase but with a large prediction uncertainty. As expected from theoretical variance decomposition rules, the contribution of sampling variance to prediction uncertainty rapidly overcomes that of process variance and dominates. Among the sources of process variance, uncertainty in the climate scenarios contributed less than 3% of the total prediction variance over a 40-year period, much less than environmental stochasticity. Our study exemplifies opportunities to improve the forecasting of complex systems using long-term studies and the challenges inherent to predicting the future of stochastic systems.

Trophic mismatch and its effects on the growth of young in an Arctic herbivore.

In highly seasonal environments, timing of breeding of organisms is typically set to coincide with the period of highest resource availability. However, breeding phenology may not change at a rate sufficient to keep up with rapid changes in the environment in the wake of climate change. The lack of synchrony between the phenology of consumers and that of their resources can lead to a phenomenon called trophic mismatch, which may have important consequences on the reproductive success of herbivores. We analyzed long-term data (1991-2010) on climate, plant phenology and the reproduction of a long-distance Arctic migrant, the greater snow goose (Chen caerulescens atlantica), in order to examine the effects of mismatched reproduction on the growth of young. We found that geese are only partially able to adjust their breeding phenology to compensate for annual changes in the timing of high-quality food plants, leading to mismatches of up to 20days between the two. The peak of nitrogen concentration in plants, an index of their nutritive quality for goslings, occurred earlier in warm springs with an early snow melt. Likewise, mismatch between hatch dates of young and date of peak nitrogen was more important in years with early snow melt. Gosling body mass and structural size at fledging was reduced when trophic mismatch was high, particularly when the difference between date of peak nitrogen concentration and hatching was >9days. Our results support the hypothesis that trophic mismatch can negatively affect the fitness of Arctic herbivores and that this is likely to be exacerbated by rising global temperatures.

Effects of experimental warming on nitrogen concentration and biomass of forage plants for an arctic herbivore

Summary In many arctic herbivores, the growth of young depends upon a synchrony between hatching date and seasonal change in plant nutritive quality. If plants respond more quickly than herbivores to climate warming, this may cause a mismatch between the availability of high‐quality food and the hatching of young. This study examines the impact of experimental warming on the main food plants of an arctic herbivore, the greater snow goose (Chen caerulescens atlanticaL.) breeding on Bylot Island, Nunavut, Canada. During summers 2007–2009, we increased the temperature using small glasshouses (open‐top chambers, OTC) in two habitats, wetlands and mesic tundra. Every 10 days, we measured above‐ground plant biomass and a proxy of nutritive quality, nitrogen concentration, of graminoid plants in warmed and control plots from snowmelt in June until late July. Open‐top chambers increased mean maximum temperature by up to 2.0 °C in wetlands and 4.6 °C in mesic tundra. Annual warming significantly increased biomass of graminoids by up to 29% in wetlands and 20% in mesic tundra. There was no difference in nitrogen concentration of the four plant species sampled (Dupontia fisheri, Eriophorum scheuchzeri, Arctagrostis latifolia and Luzula spp.) early in the season, but the seasonal decline in nitrogen occurred more rapidly in warmed than in control plots (10% to 14% less nitrogen in warmed plots in July). This effect was consistent across the 3 years of the experiment and independent of annual variation in plant phenology. There was either a weak positive effect or no effect of the warming treatment on the nitrogen biomass of plants depending on species or period of the season. Synthesis. Our results show that warming speeds up plant phenology and the seasonal decline in nutritive quality for arctic herbivores. Because young herbivores like geese are highly sensitive to the nitrogen concentration of their food, a warmer climate will likely reduce their growth. Climate warming may therefore have a negative impact on the population dynamic of arctic herbivores by reducing the quality of their summer forage.

Variations in band reporting rate and implications for kill rate in Greater Snow Geese

Souchay, G., O. Gimenez, G. Gauthier, and R. Pradel. 2014. Variations in band reporting rate and implications for kill rate in Greater Snow Geese. Avian Conservation and Ecology 9(1): 1.http://dx.doi.org/10.5751/ACE-00628-090101

Temporal variation of juvenile survival in a long-lived species: the role of parasites and body condition

Studies of population dynamics of long-lived species have generally focused on adult survival because population growth should be most sensitive to this parameter. However, actual variations in population size can often be driven by other demographic parameters, such as juvenile survival, when they show high temporal variability. We used capture-recapture data from a long-term study of a hunted, migratory species, the greater snow goose (Chen caerulescens atlantica), to assess temporal variability in first-year survival and the relative importance of natural and hunting mortality. We also conducted a parasite-removal experiment to determine the effect of internal parasites and body condition on temporal variation in juvenile survival. We found that juvenile survival showed a higher temporal variability than adult survival and that natural mortality was more important than hunting mortality, unlike in adults. Parasite removal increased first-year survival and reduced its annual variability in females only. Body condition at fledging was also positively correlated with first-year survival in treated females. With reduced parasite load, females, which are thought to invest more in their immune system than males according to Bateman's principle, could probably reallocate more energy to growth than males, leading to a higher survival. Treated birds also had a higher survival than control ones during their second year, suggesting a developmental effect that manifested later in life. Our study shows that natural factors such as internal parasites may be a major source of variation in juvenile survival of a long-lived, migratory bird, which has implications for its population dynamics.

Stable associations within flocks of Greater Snow Geese (Chen caerulescens atlantica): Do they exist beyond family bonds?

ABSTRACT. Understanding the nature of social groups may help explain the genetic structure of populations. Recently, a finescale genetic structure was found in the Greater Snow Goose (Chen caerulescens atlantica) among adults captured in different brood-rearing sites. Such a structure requires assortative pairing among birds coming from the same brood-rearing site, a process that could be enhanced if individuals maintain stable associations over time. We verified whether stable groups persisted throughout the annual cycle of this migratory species. We used an 18-year data set of females marked on brood-rearing sites in the Arctic (n = 16,060) and recaptured on those sites or resighted on the breeding, staging, or wintering grounds in subsequent years. We used a probabilistic method to compare the number of associations observed with the number expected by chance alone. Our results provide no evidence that stable groups persist in flocks during migration or in winter among adult females. However, females m...

Carry‐over effects of spring hunt and climate on recruitment to the natal colony in a migratory species

Summary In long‐lived species, temporal variation in recruitment, defined as the entry of new individuals into the breeding population, can have a large effect on population growth rate. While hunting, as a management tool, is generally expected to control population size via increased mortality, it may also act by affecting recruitment. Although the impact of hunting on survival is well studied, less attention has been paid to the non‐lethal impacts of hunting on recruitment. To control the population size of the greater snow goose Chen caerulescens atlantica, an overabundant arctic‐nesting species, a spring hunting season was implemented from 1999 onwards in addition to the traditional autumn and winter hunting seasons. We investigated the potential carry‐over effect of spring hunting on recruitment of females to their natal colony on Bylot Island, Nunavut, Canada from 1992 to 2005 while accounting for other potential confounding factors, primarily climatic effects. We applied a multistate capture‐Mark‐Recapture recruitment model to a dataset of known‐age individuals (n = 12 100), combining live recaptures at the breeding colony with dead recoveries from hunters. Annual variation in recruitment probability was best explained by spring hunt and a synthetic variable combining the climatic conditions experienced during migration (extreme values of the North Atlantic Oscillation index) with conditions upon arrival at the breeding grounds (snow cover). This model accounted for 58% of the temporal variation in recruitment, while the harvest rate or the climatic index taken alone accounted for 38% each. In the year with the highest spring hunting pressure (adult harvest rate ≈6%), recruitment was reduced by up to 50% compared to years with no hunt and similar average climatic conditions. Synthesis and applications. We conclude that there was a negative impact of the spring hunt not only on survival but also on recruitment in greater snow geese. These non‐lethal effects of hunting must be considered in management decisions aimed at controlling overabundant populations where recruitment is an important driver of population growth, as occurs in geese. Our study is also relevant to other situations such as in threatened species still exposed to hunting, as consideration of non‐lethal effects of hunting may be critical for their conservation.

Harvest, survival, and abundance of midcontinent lesser snow geese relative to population reduction efforts

We assessed the effectiveness of an extensive and unprecedented wildlife reduction effort directed at a wide-ranging migratory population of geese. Population reduction efforts that targeted several populations of light geese (greater snow geese (Chen caerulescens atlantica), lesser snow geese (C. c. caerulescens), and Ross's geese (C. rossii)) began in 1999 in central and eastern North America. Such efforts were motivated by a broad consensus that abundance of these geese was causing serious ecological damage to terrestrial and salt marsh ecosystems in central and eastern parts of the Canadian Arctic and subarctic regions along Hudson Bay. Starting in February 1999, special conservation measures (or, in the U.S., a conservation order) were added to the respective federal regulations that permitted hunters to take snow geese (in parts of Canada and the U.S.) and Ross's geese (in parts of the U.S.) during specified harvest periods outside of the hunting season. These measures were accompanied by increase or removal of daily kill and possession limits and by permissions to use previously prohibited equipment for hunting these species in certain regions of the continent. The intent was to reduce adult survival through increased hunting mortality, which was judged to be the most cost-effective approach to reversing population growth. Our principal goal was to assess the effectiveness of reduction efforts directed at the midcontinent population of lesser snow geese, which was thought to be the most serious threat to arctic and subarctic ecosystems of the 3 light goose populations. Our multiple objectives included the estimation and detection of change in the response measures of total annual harvest, harvest rate, survival rate, and abundance, using the 1998 hunting period (defined as 1 Aug 1998 to 31 Jul 1999) as a point of reference. We used information about hunter recoveries of leg- banded snow geese and estimates of regular-season harvest to estimate 1) conservation-order harvest and total annual harvest, 2) geographic and temporal distribution of recoveries by age class, 3) survival and recovery probability, and 4) abundance of snow geese each August using Lincoln's (1930) method. We also modeled population growth to infer the form of population response to management efforts. Toward that end, we also proposed a method of estimating conservation-order harvest and tested for differences in band-reporting rate between Canada and the United States. Overall, the balance of evidence favored the conclusion that the midcontinent population has continued to grow during the conservation order, although perhaps at a reduced rate. We suggest that annual rate of population growth ð^ lÞ, derived from estimates of annual population size in August, likely provides the most reliable inference about change in the midcontinent population. There was a decline in annual survival probability between these 2 periods from about 0.89 to about 0.83 among snow geese from the southern-nesting stratum (south of 608N latitude), thought to compose about 10% of the midcontinent population. However, we detected no change in the much larger northern-nesting stratum (north of 608N latitude), where annual survival remained at about 0.87 from 1989 to 2006. Thus, the conclusion that this population continued to increase during the conservation order was largely consistent with the finding that a weighted-survival probability for midcontinent snow geese essentially did not change between the period preceding (1989-1997) and during (1998-2006) the conservation order. Consistent with high survival rates were low harvest rates, which increased from 0.024 during 1989-1997 for northern geese to only 0.027 during 1998-2006 and from 0.031 to only 0.037 for southern geese. Despite the initial increase associated with the conservation order, harvest rates declined during the conservation order for geese from both strata. We suggest that the higher harvest rate evident for