Goose Colony Research Articles

Predator-mediated interactions through changes in predator home range size can lead to local prey exclusion.

The strength of indirect biotic interactions is difficult to quantify in the wild and can alter community composition. To investigate whether the presence of a prey species affects the population growth rate of another prey species, we quantified predator-mediated interaction strength using a multi-prey mechanistic model of predation and a population matrix model. Models were parametrized using behavioural, demographic and experimental data from a vertebrate community that includes the arctic fox (Vulpes lagopus), a predator feeding on lemmings and eggs of various species such as sandpipers and geese. We show that the positive effects of the goose colony on sandpiper nesting success (due to reduction of search time for sandpiper nests) were outweighed by the negative effect of an increase in fox density. The fox numerical response was driven by changes in home range size. As a result, the net interaction from the presence of geese was negative and could lead to local exclusion of sandpipers. Our study provides a rare empirically based model that integrates mechanistic multi-species functional responses and behavioural processes underlying the predator numerical response. This is an important step forward in our ability to quantify the consequences of predation for community structure and dynamics.

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.

Hopping species and borders: detection of Bartonella spp. in avian nest fleas and arctic foxes from Nunavut, Canada

BackgroundIn a warmer and more globally connected Arctic, vector-borne pathogens of zoonotic importance may be increasing in prevalence in native wildlife. Recently, Bartonella henselae, the causative agent of cat scratch fever, was detected in blood collected from arctic foxes (Vulpes lagopus) that were captured and released in the large goose colony at Karrak Lake, Nunavut, Canada. This bacterium is generally associated with cats and cat fleas, which are absent from Arctic ecosystems. Arctic foxes in this region feed extensively on migratory geese, their eggs, and their goslings. Thus, we hypothesized that a nest flea, Ceratophyllus vagabundus vagabundus (Boheman, 1865), may serve as a vector for transmission of Bartonella spp.MethodsWe determined the prevalence of Bartonella spp. in (i) nest fleas collected from 5 arctic fox dens and (ii) 37 surrounding goose nests, (iii) fleas collected from 20 geese harvested during arrival at the nesting grounds and (iv) blood clots from 57 adult live-captured arctic foxes. A subsample of fleas were identified morphologically as C. v. vagabundus. Remaining fleas were pooled for each nest, den, or host. DNA was extracted from flea pools and blood clots and analyzed with conventional and real-time polymerase chain reactions targeting the 16S-23S rRNA intergenic transcribed spacer region.ResultsBartonella henselae was identified in 43% of pooled flea samples from nests and 40% of pooled flea samples from fox dens. Bartonella vinsonii berkhoffii was identified in 30% of pooled flea samples collected from 20 geese. Both B. vinsonii berkhoffii (n = 2) and B. rochalimae (n = 1) were identified in the blood of foxes.ConclusionsWe confirm that B. henselae, B. vinsonii berkhoffii and B. rochalimae circulate in the Karrak Lake ecosystem and that nest fleas contain B. vinsonii and B. henselae DNA, suggesting that this flea may serve as a potential vector for transmission among Arctic wildlife.

Qanuq ukua kanguit sunialiqpitigu?(What should we do with all of these geese?) Collaborative research to support wildlife co-management and Inuit self-determination

Inuit living in Nunavut have harvested light geese and lived near goose colonies for generations. Inuit knowledge includes important information about light goose ecology and management that can inform co-management and enhance scientific research and monitoring. Since the 1970s, populations of light geese (Snow and Ross’ Geese; kanguit and kangunnait in Inuktut; Chen caerulescens (Linnaeus, 1758) and Chen rossii (Cassin, 1861)) have experienced significant increases in abundance which led to habitat alteration in some portions of the central and eastern Canadian Arctic. In response to concerns expressed by Inuit and wildlife managers about light goose abundance, we conducted a collaborative research project in Arviat and Salliq (Coral Harbour), Nunavut, aiming to mobilize and document Inuit knowledge about light goose ecology and management in the Kivalliq region. Here, we explore the potential of collaborative research for mobilizing Inuit knowledge to support informed and inclusive decision-making about wildlife resources. First, we describe the participatory research methods employed to explore Inuit-identified management recommendations for light geese and engage co-management partners and research contributors to explore select management options. Then, we present these light goose management recommendations and options. Lastly, we discuss opportunities and challenges around the use of collaborative research to support wildlife co-management and Inuit self-determination.Inuit nunaqaqtut Nunavuumi angunasuksimalirmata kanguqpangnik kangurniglu nunaqarvingita sanianni araagunik unuqtunnik. Inuit qaujimaningat ilaqaqpuq aturnilingnik kanguit niqinginnik mianirijauninginniklu tusaumatitaulutik qaujisarningit mianiriyaunigillu. Taimangat 1970s atuqtilugit, kanguit unirningit (kanguit amma kanguaryuit Inuktut; Chen caerulescens (Linnaeus, 1758) amma Chen rossii (Cassin, 1861)) ayunganaqtukut pisimangmata unulialiqlutik amma niqiqatiarungnauqlutik Kanataup uqiuktaqtunngani. Tamana piblugu Inuit uumayuliriyillu isumaalulirmata kanguit unulualirninginnik, taima qaujisarnirmik pigialauqpugut Arvianni and Sallim (Coral Harbour), Nunavuumi, aulataulutik amma qaujisagaulutik Inuit kaujimajagit kangurnik Kivallirmi. Tavani atuqtuuluaqtunik qaujisarnirmut mianiqsinirmullu pitaqaqpuq Inuit nagminiq isumaliurlutik nirjutinut atugaksanullu. Sivullirmik, qaujisarniup qanuinninga isumagilugu kanguit mianirijauninginut. Amma suli, uqausirilirlugu kanguit mianirijauningat atugaujuuluaqtullu. Kingulirmik, uqausirilugu atuinnaujut amma ajurutaujut qaujisarniup iluanni nirjutinik amma Inuit nagminiq aulatuulualirninginnik.

Pulsed food resources affect reproduction but not adult apparent survival in arctic foxes.

As top or mesopredators, carnivores play a key role in food webs. Their survival and reproduction are usually thought to be influenced by prey availability. However, simultaneous monitoring of prey and predators is difficult, making it challenging to evaluate the impacts of prey on carnivores' demography. Using 13years of field data on arctic foxes Vulpes lagopus in the Canadian High Arctic and a capture-recapture multi-event statistical approach, we investigated the hypothesis that increases in lemming abundance (a cyclic and unpredictable food source) and goose colony proximity (a stable but spatially and temporally limited food source) would be associated with increased apparent survival and reproduction probabilities of adults. Adult apparent survival varied greatly across years (0.13-1.00) but was neither affected by lemming nor goose variations in abundance. However, reproduction probabilities were strongly influenced by both lemming abundance and access to the goose colony. A fox breeding in the best conditions of food availability (year of high lemming density inside the goose colony) had a reproduction probability four times higher than one experiencing the worst conditions (year of low lemming density outside the goose colony). Breeding status of individuals also played a role, with breeders having a 10-20% higher probability of survival and 30% higher probability of reproduction the following year than non-breeders. As the Arctic ecosystem changes due to increased temperatures and species ranges, this study will allow better predictions of predator responses to management or environmental changes and a better understanding of ecosystem functioning.

A phenological comparison of grizzly (Ursus arctos) and polar bears (Ursus maritimus) as waterfowl nest predators in Wapusk National Park

Relatively little is known about the feeding ecology of grizzly bears (Ursus arctos) in Wapusk National Park. Other ursids, polar bears (Ursus maritimus), are well known predators of waterfowl nests in the area, and grizzly bears could feasibly make use of such resources. However, since the arrival of polar bears on land in the spring is largely dependent on date of sea-ice breakup, the timing of predation by each bear species may differ. We investigated the timing of bear predation in common eider (Somateria mollissima sedentaria) and lesser snow goose (Anser caerulescens caerulescens) colonies from 2012 to 2018 using nest cameras. We observed grizzlies consuming eggs of both species in all years except 2013 and confirmed that at least two individual grizzlies occupied the park in 2016. In the 3 years when both grizzly and polar bears were detected, grizzlies were observed earlier in the year than polar bears and had greater overlap with an estimated availability index of incubating waterfowl. We hypothesize that grizzly bears could have earlier access to waterfowl eggs in the park, potentially reducing availability of these terrestrial foods to polar bears.

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.

Spatio-temporal responses of predators to hyperabundant geese affect risk of predation for sympatric-nesting species.

The Arctic is undergoing rapid changes, with anthropogenic shifts in climate having important and well-documented impacts on habitat. Populations of predators and their prey are affected by changing climate and other anthropogenic factors, and these changing trophic interactions could have profound effects on breeding populations of Arctic birds. Variable abundance of lemmings (a primary prey of generalist Arctic predators) and increasing abundance of light geese (Lesser Snow and Ross’ Geese; a secondary prey) could have negative consequences for numerous sympatric shorebirds (an incidental prey). Using 16 years of predator-prey observations and 13-years of shorebird nest survival data at a site near a goose colony we identify relationships among geese, lemmings, and their shared predators and then relate predator indices to shorebird risk of nest predation. During two years, we also placed time-lapse cameras and artificial shorebird nests at increasing distances from a goose colony to document spatial trends in predators and their effect on risk of predation. In the long-term data, yearly indices of light geese positively influenced indices of gulls and jaegers, and shorebird nest predation rate was negatively correlated with jaeger and fox indices. All three predator indices were highest near the goose colony and artificial nest predation probability was negatively correlated with distance from goose colony, but these effects were less apparent during the second year. Combined, these results highlight the variation in predator-mediated interactions between geese and shorebirds and outline one mechanism by which hyperabundant geese may be contributing to local or regional declines in Arctic-nesting shorebird populations.

Broad‐scale changes in tundra‐nesting bird abundance in response to hyperabundant geese

AbstractEnvironmental changes can propagate through food webs in complex ways via trophic cascades. In the North American Arctic, hyperabundant populations of geese are causing significant habitat change and the resulting trophic cascades are known to impact plant and invertebrate communities. However, the potential impacts on other tundra‐nesting birds are not fully understood. Here, we evaluate the impacts of light geese (Snow Geese, Chen caerulescens, and Ross’ Goose, Chen rossii) populations on other tundra‐nesting birds, using count data collected during bird surveys conducted at varying distances from light goose colonies across the Canadian Arctic. From a dataset of 920 12–16 ha plots distributed across the Canadian Arctic, we identified 527 that were within 200 km of the mapped extent of known light goose colonies. After accounting for regional variation, we demonstrate that densities of most Cover‐Nesting Shorebirds and passerines are depressed in the vicinity of light goose colonies. We suggest that these trends are the results of the combined effects of goose‐induced changes in habitat and predator–prey interactions. These direct and indirect effects of light geese could be contributing to the declines experienced by some tundra‐nesting bird populations in parts of their range. Ongoing climate‐related changes to habitat, predators, and arthropods could interact with this effect of geese to further alter the suitability of tundra habitats for Arctic‐breeding birds, in additive or even unanticipated ways.

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.

The Lesser Snow Goose on Wrangel Island: Trophic Interactions with Ruminants and Breeding Habitat Selection

The lesser snow goose (Anser caerulescens caerulescens) has been exterminated across a vast area of Eurasia. At present, it is unable to regenerate there, though its population in North America has reached fifteen million. In Eurasia, the only major nesting colony still persists on Wrangel Island, where the geese use the trophic resources together with ruminants. An assessment of the competitive networks and the trophic interactions between the geese and the ruminants was performed. The analysis of the significance of the trophic niche overlap and the competitive advantages of geese in the habitat preferences has proved that the ruminants are stronger competitors for trophic resources than the geese. It has been ascertained that the levels of competition for trophic resources and/or resource shortages are higher across the habitats of most types associated with the goose colony. The level of the competition for trophic resources is lower, and the feed resources are more diverse and abundant in the habitats that are used by the geese after leaving the colony. It can be concluded that the shortage of resources and/or the stronger competitors for trophic resources (the ruminants) cannot prevent restoration of extinct colonies or the formation of new colonies with a recent increase in the size of the goose population on Wrangel Island. The distribution, abundance, and quality of trophic resources and the competition for them with ruminants do not determine the goose choice of a habitat for a nesting colony. The choice depends on the microclimate and, probably, on a range of other factors.

Components of population growth for Arctic foxes at a large Arctic goose colony: the relative contributions of adult survival and recruitment

ABSTRACTThe abundance and distribution of animals often vary dramatically among years in Arctic environments. Such variation, in turn, is closely related to changes in food abundance and its effect on vital rates such as survival and recruitment. However, the relative importance of survival and recruitment to changes in population growth and how this varies with fluctuations in food abundance and climatic variation is poorly understood for most animals. The objective of this study was to examine how the relative importance of adult survival and recruitment to population change by Arctic foxes varies in relation to fluctuations in food abundance and climatic variation. Specifically, we used capture–recapture models to estimate how apparent adult survival and recruitment of Arctic foxes at a large Arctic goose colony varied in response to small mammal abundance, the numbers of two species of nesting geese and climate variation indexed by the Arctic Oscillation. Analyses of live capture data collected at Kar...

Predator‐mediated negative effects of overabundant snow geese on arctic‐nesting shorebirds

AbstractOverabundant species can strongly impact ecosystem functioning through trophic cascades. The strong increase in several arctic geese populations, primarily due to changes in agricultural practices in temperate regions, can have severe direct impacts on tundra ecosystems through vegetation degradation. However, predator‐mediated negative effects of goose overabundance on other tundra species can also be significant but are poorly understood. We tested the hypothesis that goose abundance negatively affects arctic‐nesting shorebirds by increasing nest predation pressure. We used six years of data collected within and near a greater snow goose colony (Chen caerulescens atlantica) to evaluate the effect of geese on the spatial variation in (1) the occurrence of shorebird nest predators, (2) the nest predation risk (with artificial shorebird nests), and (3) the occurrence of nesting shorebirds. We found that the goose colony had a strong influence on the spatial distribution of nest predators and nesting shorebirds. Occurrence of predators decreased, while occurrence of nesting shorebirds increased with distance from the centroid of the colony. The strength of these effects was modulated by lemming density, the preferred prey for predators. Shorebird nest predation risk also decreased with distance from the colony. Overall, these results indicate that goose abundance negatively affects arctic‐nesting shorebirds through shared predators. Therefore, we show that the current decline of some arctic shorebird populations may be in part mediated by a negative effect of an overabundant species.

Do hyperabundant Arctic-nesting geese pose a problem for sympatric species?

Arctic-breeding geese are at record high population levels and are causing significant changes to some of their breeding and staging habitats. These changes could influence sympatric wildlife, but the nature and strength of these effects are unknown. Here, we review the interactions between geese and sympatric species and propose future research that could help to fill important knowledge gaps. We suggest that geese may be indirectly affecting other species through changes to nesting habitat, prey availability, and predator–prey interactions. Many ground-nesting Arctic birds prefer vegetated wet tundra habitats that offer concealed nest sites; areas also heavily used by breeding and staging geese. Where goose foraging exceeds the capacity of the plants to regenerate, habitats have shorter graminoids and more exposed substrate, potentially reducing the availability of concealed nest sites for other birds. Studies have documented local reductions in the abundance of these concealed-nesting species, such as shorebirds. Despite the nutrient enrichment contributed by goose feces, habitats heavily altered by geese have also been shown to host a reduced diversity and abundance of some invertebrate groups. In contrast, generalist predators show positive functional and numerical responses to the presence of breeding geese. Therefore, the risk of predation for alternative or incidental prey (e.g., lemmings or small bird nests) is likely elevated within or near breeding colonies. Studies have demonstrated a reduced abundance of small mammals in areas heavily used by geese, but it is unknown whether this is related to shared predators or habitat alteration. Sympatric wildlife could be further affected through higher stress-levels, altered body condition, or other physiological effects, but there is currently no evidence to demonstrate such impacts. Few studies have explored the potential effects of geese at larger spatial scales, but we suggest that hyperabundant geese could result in regional declines in the abundance and diversity of shorebirds and passerines. We recommend coordinated studies across multiple regions to quantify nesting habitat, arthropod communities, and predator–prey interactions in response to nearby goose colonies. To align with current multispecies approaches to conservation, adequate knowledge of the potential effects of hyperabundant goose populations on other wildlife should be a priority.

Ross’s Goose (<i>Chen rossi</i>) Nesting Colony at East Bay, Southampton Island, Nunavut

Most Ross’s Geese (Chen rossi) nest in the central arctic of North America, but the range has expanded eastward in the last two decades. In summer 2014, we discovered a cluster of 48 nesting pairs of Ross’s Geese at East Bay Migratory Bird Sanctuary,Southampton Island, Nunavut. The Ross’s Goose colony was between an upland Lesser Snow Goose (Chen caerulescens caerulescens) nesting area and a low-lying Cackling Goose (Branta hutchinsii) and Atlantic Brant (Branta bernicla) nesting area, in a zone dominated by ponds and lakes and interspersed with areas of moss and graminoids. Our discovery documents a previously unknown level of nesting of Ross’s Geese at East Bay and corroborates unpublished evidence of growing numbers of the species on Southampton Island and expansion of its breeding range.

ESTIMATING TOXOPLASMA GONDII EXPOSURE IN ARCTIC FOXES (VULPES LAGOPUS) WHILE NAVIGATING THE IMPERFECT WORLD OF WILDLIFE SEROLOGY.

Although the protozoan parasite Toxoplasma gondii is ubiquitous in birds and mammals worldwide, the full suite of hosts and transmission routes is not completely understood, especially in the Arctic. Toxoplasma gondii occurrence in humans and wildlife can be high in Arctic regions, despite apparently limited opportunities for transmission of oocysts shed by felid definitive hosts. Arctic foxes (Vulpes lagopus) are under increasing anthropogenic and ecologic pressure, leading to population declines in parts of their range. Our understanding of T. gondii occurrence in arctic foxes is limited to only a few regions, but mortality events caused by this parasite have been reported. We investigated the exposure of arctic foxes to T. gondii in the Karrak Lake goose colony, Queen Maud Gulf Migratory Bird Sanctuary, Nunavut, Canada. Following an occupancy-modeling framework, we performed replicated antibody testing on serum samples by direct agglutination test (DAT), indirect fluorescent antibody test (IFAT), and an indirect enzyme-linked immunosorbent assay (ELISA) that can be used in multiple mammalian host species. As a metric of test performance, we then estimated the probability of detecting T. gondii antibodies for each of the tests. Occupancy estimates for T. gondii antibodies in arctic foxes under this framework were between 0.430 and 0.758. Detection probability was highest for IFAT (0.716) and lower for DAT (0.611) and ELISA (0.464), indicating that the test of choice for antibody detection in arctic foxes might be the IFAT. We document a new geographic record of T. gondii exposure in arctic foxes and demonstrate an emerging application of ecologic modeling techniques to account for imperfect performance of diagnostic tests in wildlife species.

Patterns of predation of Pink-footed Goose nests by polar bear

This study explored patterns of predation by polar bear Ursus maritimus on the nests of Pink-footed Geese Anser brachyrhynchus on the coastal tundra stretch Nordenskioldkysten, west coast of Spitsbergen, Svalbard. Goose nests occurred in densities of up to 126 nests/km 2 (mean=6.4), at an average distance of 1.5 km from the seashore, and were mainly associated with greenstone outcrops. Open, flat areas were avoided for nesting. Goose pairs nested in colonies of up to 23 nests, with 50% of the pairs nesting in colonies larger than 5. In 2011 and 2012, polar bears invaded the Pink-footed Goose nesting area to consume goose eggs, a behaviour that they had not exhibited in previous years. Polar bears selectively visited the taller outcrops and locations with the larger number of goose nests. Moreover there was a steep gradient in predation from the seashore towards the inland, with no predation at distances greater than 1.8 km from the coastline. We expect that the predation pressure by polar bears will aggravate in the coming years when more bears learn to exploit the inland goose colonies.

Brent goose colonies near snowy owls: Internest distances in relation to breeding arctic fox densities

This study was conducted in 2005 near Medusa Bay (73 degrees 21' N, 80 degrees 32' E) and the delta of the Pyasina River (74 degrees 10' N, 86 degrees 45' E), northwest of the Taimyr Peninsula. It was shown that in the years when the numbers of the Arctic foxes are high, even though the lemming numbers are high as well, Brent geese nest considerably closer to owls' nests than in the years with low Arctic fox numbers. At values of the Arctic fox densities greater than one breeding pair per 20 km2, the factor of lemming numbers ceases to affect the distance between owl and geese nests. This distance becomes dependent on the Arctic fox density (numbers). When the Arctic fox density is greater than the pronounced threshold, the owl-Brent internest distance is inversely and linearly related to the Arctic fox density.

Erratum: Comparative survival and recovery of Ross's and lesser snow geese from Canada's central arctic

Traylor, Joshua J., Ray T. Alisauskas, Stuart M. Slattery, and Kiel L. Drake. 2012. Comparative survival and recovery of Ross's and lesser snow geese from Canada's central arctic. Journal of Wildlife Management 76:1135–1144. In this article, the x axis of Figure 6 was incorrectly labeled. The corrected Figure 6 is shown below. The publisher regrets the error. Figure 6. Relationship between juvenile survival probability for Ross's and snow geese marked north of the Karrak Lake goose colony, Nunavut, Canada, 1991–2008, in relation to mean nest initiation date. Survival estimates are model averages back-transformed from the logit scale.

Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling

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.