Explore the vast range of titles available.

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem.

Under current climate trends, spring ice breakup in Hudson Bay is advancing rapidly, leaving polar bears (Ursus maritimus) less time to hunt seals during the spring when they accumulate the majority of their annual fat reserves. For this reason, foods that polar bears consume during the ice‐free season may become increasingly important in alleviating nutritional stress from lost seal hunting opportunities. Defining how the terrestrial diet might have changed since the onset of rapid climate change is an important step in understanding how polar bears may be reacting to climate change. We characterized the current terrestrial diet of polar bears in western Hudson Bay by evaluating the contents of passively sampled scat and comparing it to a similar study conducted 40 years ago. While the two terrestrial diets broadly overlap, polar bears currently appear to be exploiting increasingly abundant resources such as caribou (Rangifer tarandus) and snow geese (Chen caerulescens caerulescens) and newly available resources such as eggs. This opportunistic shift is similar to the diet mixing strategy common among other Arctic predators and bear species. We discuss whether the observed diet shift is solely a response to a nutritional stress or is an expression of plastic foraging behavior. We analyzed scat contents to characterize the current terrestrial polar bear diet in western Hudson Bay and compared our results to a similar study done in the 1960s to see how the diet has changed since the onset of climate‐related changes. We found that polar bears are eating new foods (eggs, caribou) in relative proportion to their availability on the landscape. We discuss whether the diet shift is solely a response to nutritional stress or is another expression of plastic foraging strategy typical of other Ursids.

Breeding propensity, i.e., the probability that a mature female attempts to breed in a given year, is a critical demographic parameter in long-lived species. Life-history theory predicts that this trait should be affected by reproductive trade-offs so that the probability of future reproduction should depend on the current reproductive investment. However, breeding propensity is one of the most difficult parameters to estimate because nonbreeders are often absent from the breeding area, thereby requiring the inclusion of unobservable states in the analysis. We developed a new methodological approach by integrating a robust design sampling scheme within the multi-event capture-recapture framework. Our new model accounted for uncertainty in state assignation while allowing for departure of individuals between secondary sampling occasions. We applied this model to a long-term data set of female Greater Snow Geese ( Chen caerulescens atlantica ) to estimate breeding propensity and to investigate potential reproductive costs. We combined resightings during the nesting stage and recapture at the end of the breeding season to estimate breeding propensity and nesting success, and added recoveries to improve survival probability estimates. We found that both breeding propensity and nesting success depended upon breeding status in the previous year, though not survival. Successful breeders had a lower breeding propensity than failed breeders in the following year, but a higher nesting success. Individuals absent from the breeding colony had a low breeding propensity, but a high nesting success the following year. Our results suggest a cost of reproduction on breeding propensity in the next year, but once females decide to breed, nesting success is likely driven by individual quality. An added benefit of our model is that, unlike previous models with unobservable states, all parameters were identifiable when survival and breeding probabilities were fully state dependent. Our new multi-event framework is a flexible tool that can be applied to a large range of species to estimate breeding propensity and to investigate reproductive trade-offs.

A key question in evolutionary genetics is whether shared genetic mechanisms underlie the independent evolution of similar phenotypes across phylogenetically divergent lineages. Here we show that in two classic examples of melanic plumage polymorphisms in birds, lesser snow geese (Anser c. caerulescens) and arctic skuas (Stercorarius parasiticus), melanism is perfectly associated with variation in the melanocortin-1 receptor (MC1R) gene. In both species, the degree of melanism correlates with the number of copies of variant MC1R alleles. Phylogenetic reconstructions of variant MC1R alleles in geese and skuas show that melanism is a derived trait that evolved in the Pleistocene.

The region south of Queen Maud Gulf in Canada’s central Arctic now annually harbors several million nesting and non-breeding Ross’s ( Chen rossii ) and lesser snow geese ( C. caerulescens caerulescens ). Here, and in other Arctic and Subarctic areas, abundant goose populations have been demonstrated to have impacted biomass and composition of vegetative communities. We applied the classification scheme that Didiuk and Ferguson (Land cover mapping of Queen Maud Gulf Migratory Bird Sanctuary, Nunavut. Environment Canada, Ottawa, 2005 ) used on 1986–1992 Landsat Imagery to produce a habitat map for 2011 of the eastern portion of the Queen Maud Gulf Bird Migratory Bird Sanctuary (QMGMBS). We used a Geographic Information System for change detection between 1988 and 2011 and found a > fivefold increase in area of exposed peat habitat from 269 to 1373 km 2 in our 36,370 km 2 study area. About 323 km 2 (24) % of the area classified as exposed peat in 2011 was previously wet sedge meadow, a preferred feeding habitat of geese, and which declined from 2856 to 1488 km 2 (−48 %) in our study area. Combined open water categories declined from 9688 to 7960 km 2 (−18 %), suggesting that some of the reduction in wet sedge meadow could have been caused by drawdown. However, of the 1981 km 2 of open water that was lost between 1988 and 2011, only 142 km 2 (7 %) was classified as exposed peat and 250 km 2 (13 %) as active deposits, while 171 km 2 (9 %) was classified as wet sedge meadow. Of the remaining open water coverage that was lost, 118 km 2 (6 %) was classified as hummock or graminoid tundra, 459 km 2 (23 %) as moss-lichen or lichen-heath tundra, and 764 km 2 (39 %) as low shrub tundra/shrub thicket. Approximately 562 km 2 (41 %) of exposed peat in 2011 was formerly moss-lichen and lichen-heath tundra, upland habitats commonly used by nesting snow geese and Ross’s geese. By 2011, the proportion of ground covered by exposed peat habitat surrounding the four largest known colonies of light geese, all in the eastern half of QMGMBS, was strongly linked to the amount of previously vegetated habitat (i.e., potential exposed peat), and was inversely related to distance from colony perimeters. About 50 % of the spatial variance in coverage by exposed peat was explained by nearness to nesting by large concentrations of light geese. While some increase in exposed peat was likely a result of drier conditions in 2011 compared to 1988, spatial patterns of habitat change suggest that much of the increase in exposed peat was likely a result of intensive foraging in wet sedge meadow habitat and nest-building activities in tundra habitats by high densities of snow geese and Ross’s geese. Of the 269 km 2 of exposed peat originally identified in 1988, only 55 km 2 of it was still classified as exposed peat in 2011, but detailed ground studies will be required to determine at what rate exposed peat habitats revert back to wet sedge meadow and other vegetated tundra. We recommend comparison of habitat changes in areas with and without large populations of lesser snow geese and Ross’s geese to better assess changes caused by geese in relation to any change that may result from changes in hydrology over time.

Brachyspira is associated with diarrhea and colitis in pigs, and control of these pathogens is complicated by their complex ecology. Identification of wildlife reservoirs of Brachyspira requires the discrimination of colonized animals and those simply contaminated through environmental exposure. Lesser snow geese (Chen caerulescens caerulescens) were sampled in the Canadian arctic during the summer of 2011, and cloacal swabs were cultured on selective media. Brachyspira isolates were obtained from 15/170 (8.8 %) samples, and 12/15 isolates were similar to isolates previously recovered from pigs, including \"Brachyspira hampsonii\", a recently characterized species associated with dysentery-like disease in pigs in North America. A pilot inoculation study with one strongly β-hemolytic B. hampsonii isolate resulted in fecal shedding of the isolate by inoculated pigs for up to 14 days post-inoculation, but no severe clinical disease. Results of this study indicate that lesser snow geese can be colonized by Brachyspira strains that can also colonize pigs. Millions of lesser snow geese (C. caerulescens caerulescens) travel through the major pork-producing areas of Canada and the USA during their annual migration, making them a potential factor in the continental distribution of these bacteria.

1. Understanding how climate change will affect animal population dynamics remains a major challenge, especially in long-distant migrants exposed to different climatic regimes throughout their annual cycle. 2. We evaluated the effect of temperature throughout the annual cycle on demographic parameters (age-specific survival and recruitment, breeding propensity and fecundity) of the greater snow goose (Chen caerulescens atlantica L.), an arctic-nesting species. As this is a hunted species, we used the theory of exploited populations to estimate hunting mortality separately from natural mortality in order to evaluate climatic effects only on the latter form of mortality. 3. Our analysis was based on a 22-year marking study (n = 27 150 females) and included live recaptures at the breeding colony and dead recoveries from hunters. We tested the effect of climatic covariates by applying a procedure that accounts for unexplained environmental variation in the demographic parameter to a multistate capture-mark-recapture recruitment model. 4. Breeding propensity, clutch size and hatching probability all increased with high temperatures on the breeding grounds. First-year survival to natural causes of mortality increased when temperature was high at the end of the summer, whereas adult survival was not affected by temperature. On the contrary, accession to reproduction decreased with warmer climatic conditions during the non-breeding season. 5. Survival was strongly negatively related to hunting mortality in adults, as expected, but not in first-year birds, which suggests the possibility of compensation between natural and hunting mortality in the latter group. 6. We show that events occurring both at and away from the breeding ground can affect the demography of migratory birds, either directly or through carryover effects, and sometimes in opposite ways. This highlights the need to account for the whole life cycle of an animal when attempting to project the response of populations to future climatic changes.

Environmental constraints are strong in migratory species that breed in the Arctic. In addition to breeding, Anatidae have to renew all their flight feathers during the short arctic summer. We examine how temporal constraints and climate affect the phenology of flight feather moult in the greater snow goose Chen caerulescens atlantica, a High Arctic nesting species. We used a database of 1412 moulting adult females measured over 15 yr on Bylot Island, Nunavut. Ninth (9th) primary length was used to determine the moult stage and speed of feather growth. We found a positive relationship between median annual hatching and moult initiation dates and the slope did not differ from 1. The interval between hatching and moult initiation was thus rather fixed and geese did not initiate moult earlier when reproductive phenology was delayed. Nonetheless, there was no relationship between median hatching date and the date at which birds regained flight capacity, suggesting that date of end of moult is independent of the reproductive phenology. There was a trend for an increase in the speed of flight feather growth in years with delayed hatching date. This is the most likely mechanism that could explain moult phenology adjustment in this species. Finally, we found a positive relationship between 9th primary length (corrected for inter-annual variations) and body condition, suggesting a delay in moulting for individuals in poor condition. These results suggest that moult plasticity is primarily governed by variations in feather growth speed. This phenotypic plasticity could be necessary to complete flight feather renewal before the end of the arctic summer, independently of reproductive phenology and spring environmental conditions. Our novel results suggest possible phenological adjustments through moult speed, which was considered constant in geese until now.

The relative allocation of endogenous- and exogenous-derived nutrients to reproductive investment in Arctic-nesting geese is affected by body size, migration distance, and proximate conditions on the wintering, staging, and breeding grounds prior to clutch initiation. We used δ13C and δ15N measurements of muscle tissue and egg lipid-free yolk and albumen and δ13C analysis of abdominal fat and egg yolk lipids, together with isotopic analyses of foraging plants, to quantify the relative use of endogenous and exogenous reserves in egg production in a breeding population of sub-Arctic Lesser Snow Geese (Chen caerulescens caerulescens) on the Cape Churchill Peninsula, Manitoba, from 2005 to 2008. We used a concentration-dependent, two-isotope, three-source Bayesian (SIAR) mixing model to derive estimates of endogenous reserves to egg macronutrients and a single-isotope (δ13C), two-source (exogenous vs. endogenous) Bayesian model to estimate the source of lipids to eggs. Endogenous protein contributions to eggs were similar to those found using identical Bayesian analytical methods for the larger-bodied Greater Snow Goose (Chen caerulescens atlantica) breeding in the Canadian High Arctic and were on the order of 30%. However, endogenous lipid contributions were considerably greater for the population of Lesser Snow Geese (mean annual contribution of 55.5% vs. 22.3%). This suggests that advantages of larger body size for transport of body lipid reserves for long distances may be countered by the need to use lipids to fuel migration over greater distances. In addition, feeding opportunities of Greater Snow Geese upon arrival at their more distant breeding sites were likely adequate to offset a shorter breeding season and longer development times for offspring than at lower-latitude sites.

\\textcopyright 2015 The Wildlife Society. \\textcopyright The Wildlife Society, 2015.Adaptive management of harvested waterfowl requires accurate estimations of demographic parameters. These must also be representative of the targeted population. In the greater snow goose, all demographic parameters so far have been estimated from long-term banding conducted at a single nesting colony in the Arctic, Bylot Island, where 15% of the population breeds. We used data from a second banding program conducted on Ellesmere Island, 800km north of Bylot Island and near the northern limit of the breeding range, to compare adult survival between these 2 breeding sites over the period 2007-2011. This allowed us to determine the representativeness of demographic parameters estimated from the Bylot colony. We used a multi-event capture-recapture model combining recaptures, resightings of neckbanded birds, and recoveries on a seasonal basis, which allowed us to test specifically for differences in survival during the migration periods. Despite differences in migration distance (20% longer for Ellesmere Island) and environmental conditions, survival rate of birds from these 2 breeding sites were similar in all seasons. Annual survival ranged from 0.72 to 0.79. This apparent absence of a cost of migration on survival may be explained by the canalization hypothesis: variance in adult survival of the greater snow goose, a long-lived species, caused by environmental factors may have been reduced because of selection pressure on this trait, which is closely linked to fitness. The absence of spatial variation in adult survival suggests that the extrapolation of survival parameters estimated from the Bylot Island colony to the entire population may be valid.