Evidence of Territoriality and Species Interactions from Spatial Point-Pattern Analyses of Subarctic-Nesting Geese

Quantifying spatial patterns of bird nests and nest fate provides insights into processes influencing a species’ distribution. At Cape Churchill, Manitoba, Canada, recent declines in breeding Eastern Prairie Population Canada geese (Branta canadensis interior) has coincided with increasing populations of nesting lesser snow geese (Chen caerulescens caerulescens) and Ross’s geese (Chen rossii). We conducted a spatial analysis of point patterns using Canada goose nest locations and nest fate, and lesser snow goose nest locations at two study areas in northern Manitoba with different densities and temporal durations of sympatric nesting Canada and lesser snow geese. Specifically, we assessed (1) whether Canada geese exhibited territoriality and at what scale and nest density; and (2) whether spatial patterns of Canada goose nest fate were associated with the density of nesting lesser snow geese as predicted by the protective-association hypothesis. Between 2001 and 2007, our data suggest that Canada geese were territorial at the scale of nearest neighbors, but were aggregated when considering overall density of conspecifics at slightly broader spatial scales. The spatial distribution of nest fates indicated that lesser snow goose nest proximity and density likely influence Canada goose nest fate. Our analyses of spatial point patterns suggested that continued changes in the distribution and abundance of breeding lesser snow geese on the Hudson Bay Lowlands may have impacts on the reproductive performance of Canada geese, and subsequently the spatial distribution of Canada goose nests.     

Decadal Response of Arctic Freshwaters to Burgeoning Goose Populations

The Arctic is faced with rapid climatic changes, but in some areas, drastic changes in the abundance of herbivores represent an even greater agent of change. Increasing goose populations, especially midcontinent lesser snow geese (Chen caerulescens), have led to an extensive loss of vegetation in terrestrial habitats in the Arctic through heavy grazing and destructive foraging. Our aim was to evaluate the effect of geese on the freshwater systems in their Arctic breeding grounds. We sampled the water chemistry of lakes and ponds across a major goose breeding area in the Eastern Canadian Arctic and compared results to samples taken 13 years earlier to determine whether the changes in water chemistry, if evident, were consistent with effects of geese or of climate. Our results suggest that nutrient loadings have increased while most other parameters associated with the underlying geology and hydrology of the region have stayed in a similar range as a decade ago. The most significant changes were linked to nitrogen and phosphorus; phosphorus concentrations doubled between 2001/2002 and 2015, with the highest levels and greatest changes observed for wetlands inside versus outside of goose breeding areas. Our results suggest that geese are most strongly affecting nutrient loads in freshwaters inside breeding areas, which show evidence of ornithological eutrophication. Nutrient changes of this magnitude, especially in typically oligotrophic Arctic lakes, can have profound consequences on ecosystem structure and function and demonstrate how burgeoning waterfowl populations can act as a vector of rapid environmental change in Arctic freshwaters.     

Disturbance Caused by Aerial Waterfowl Surveys During the Nonbreeding Season

Aerial surveys flown at low altitudes allow detection, identification, and enumeration of waterfowl and other waterbirds, but few studies have assessed disturbance to these guilds during the nonbreeding period. Excessive disturbance can potentially increase energy expenditure and exposure to hunting mortality contrary to objectives of many waterfowl sanctuaries where surveys are conducted. We used concurrent ground and aerial surveys to estimate the proportion of waterfowl and other waterbirds that exhibited a noticeable reaction (i.e., disturbance) or left the survey area entirely (i.e., abandonment) during low-altitude (i.e., 60–90 m above ground level) aerial surveys during September through January 2014–2017 in Illinois, USA. Overall, disturbance and abandonment probabilities of waterfowl (x̄ = 14 ± 2% [SE] and x̄ = 3 ± 1%, respectively) during aerial surveys were low. However, disturbance and abandonment probabilities varied considerably among taxa (e.g., American coot [Fulica americana] x̄ = 2 ± 1% and x̄ = 0 ± 0%, respectively; killdeer [Charadrius vociferus] x̄ = 92 ± 8% and x̄ = 17 ± 17%, respectively). Additionally, disturbance and abandonment probabilities of light geese (i.e., snow goose [Chen caerulescens] and Ross's goose [C. rossii]) and greater white-fronted geese (Anser albifrons) were relatively high, and nearly all light geese abandoned a survey location as a result of the aerial survey. Among waterfowl taxa, the odds of disturbance from the survey aircraft were 2.2–6.2 times greater at locations closed to waterfowl hunting than locations open to waterfowl hunting. Temperature, wind speed, and cloud cover were not important predictors of disturbance for most guilds, except for a negative influence of temperature on disturbance of geese. Low-altitude aerial surveys were not a significant source of disturbance for many taxa and abandonment events were rare, except events involving light geese. Periodic low-altitude aerial surveys appear to be compatible with objectives of providing sanctuary conditions for most waterfowl and other waterbirds. © 2020 The Wildlife Society.     

Weather-Related Indices of Autumn– Winter Dabbling Duck Abundance in Middle North America

ABSTRACT Research on effects of key weather stimuli influencing waterfowl migration during autumn and winter is limited. We investigated relationships between changes in relative abundances of mallard (Anas platyrhynchos) and other dabbling ducks (Anas spp.) and weather variables at midlatitude locations in North America. We used waterfowl survey data from Missouri Conservation Areas and temperature and snow cover data from the Historical Climatology Network to evaluate competing models to explain changes in relative abundance of ducks in Missouri, USA, during autumn-winter, 1995–2005. We found that a cumulative weather severity index model (CumulativeWSI; calculated as mean daily temp - degrees C + no. of consecutive days with mean temp ≤ 0° C + snow depth + no. of consecutive days with snow cover) had the greatest weight of evidence in explaining changes in relative abundance of ducks. We concluded the CumulativeWSI reflected current and cumulative effects of ambient temperatures on energy expenditure by ducks, and snow cover and wetland icing, on food availability for ducks. The CumulativeWSI may be useful in determining potential changes in autumn-winter distributions of North American waterfowl given different climate change projections and associated changes in habitat conservation needs. Future investigations should address interactions between CumulativeWSI and landscape habitat quality, regional waterfowl populations, hunter harvest, and other anthropogenic influences to increase understanding of waterfowl migration during autumn-winter.     

Changes in Agriculture and Abundance of Snow Geese Affect Carrying Capacity of Sandhill Cranes in Nebraska

ABSTRACT The central Platte River valley (CPRV) in Nebraska, USA, is a key spring-staging area for approximately 80% of the midcontinent population of sandhill cranes (Grus canadensis; hereafter cranes). Evidence that staging cranes acquired less lipid reserves during the 1990s compared to the late 1970s and increases in use of the CPRV by snow geese (Chen caerulescens) prompted us to investigate availability of waste corn and quantify spatial and temporal patterns of crane and waterfowl use of the region. We developed a predictive model to assess impacts of changes in availability of corn and snow goose abundance under past, present, and potential future conditions. Over a hypothetical 60-day staging period, predicted energy demand of cranes and waterfowl increased 87% between the late 1970s and 1998–2007, primarily because peak abundances of snow geese increased by 650,000 and cranes by 110,000. Compared to spring 1979, corn available when cranes arrived was 20% less in 1998 and 68% less in 1999; consequently, the area of cornfields required to meet crane needs increased from 14,464 ha in 1979 to 32,751 ha in 1998 and 90,559 ha in 1999. Using a pooled estimate of 88 kg/ha from springs 1998–1999 and 2005–2007, the area of cornfields needed to supply food requirements of cranes and waterfowl increased to 65,587 ha and was greatest in the eastern region of the CPRV, where an estimated 54% of cranes, 47% of Canada geese (Branta canadensis), 45% of greater white-fronted geese (Anser albifrons), and 46% of snow geese occurred during ground surveys. We estimated that a future reduction of 25% in available corn or cornfields would increase daily foraging flight distances of cranes by 27–38%. Crane use and ability of cranes to store lipid reserves in the CPRV could be reduced substantially if flight distance required to locate adequate corn exceeded a physiological maximum distance cranes could fly in search of food. Options to increase carrying capacity for cranes include increasing accessibility of cornfields by restoring degraded river channels to disperse roosting cranes and increasing wetland availability in the Rainwater Basin to attract snow geese using the CPRV.     

Does snowmelt constrain spring migration progression in sympatric wintering Arctic-nesting geese? Results from a Far East Asia telemetry study

Telemetry data from sympatric Eastern Tundra Bean Geese Anser serrirostris captured on their winter quarters in the Yangtze River Floodplain, China, tracked to two discrete breeding areas (the Anadyr Region (AR) at 65°N and Central Russian Arctic (CRA) at 75°N) showed that, despite longer migration distance (6300 vs. 5300 km), AR geese reached their destination 23 days earlier than CRA geese as a result of increasingly delayed date of 50% snow cover along the route of CRA geese (based on satellite imagery data). Both groups arrived at breeding areas 8–9 days prior to the local date of 50% snow cover thaw, suggesting optimal timing of arrival for subsequent reproduction. Despite small sample sizes from one season of tracking, these intra-specific data are the first to suggest that, in time-limited Arctic-nesting geese, snowmelt conditions regulated the individual progress and duration of spring migration along the flyway to coincide with arrival at optimal spring conditions on breeding areas.     

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

Large increases in several populations of North American arctic geese have resulted in ecosystem-level effects from associated herbivory. Consequently, some breeding populations have shown density dependence in recruitment through declines in food availability. Differences in population trajectories of lesser snow geese (Chen caerulescens caerulescens; hereafter snow geese) and Ross's geese (C. rossii) breeding in mixed-species colonies south of Queen Maud Gulf (QMG), in Canada's central arctic, suggest that density dependence may be limiting snow goose populations. Specifically, long-term declines in age ratios (immature:adult) of harvested snow geese may have resulted from declines in juvenile survival. Thus, we focused on juvenile (first-year) survival of snow and Ross's geese in relation to timing of reproduction (annual mean nest initiation date) and late summer weather. We banded Ross's and snow geese from 1991 to 2008 in the QMG Migratory Bird Sanctuary. We used age-structured mark-recapture models to estimate annual survival rates for adults and juveniles from recoveries of dead birds. Consistent with life history differences, juvenile snow geese survived at rates higher than juvenile Ross's geese. Juvenile survival of both species also was lower in late seasons, but was unrelated to arctic weather measured during a 17-day period after banding. We found no evidence of density dependence (i.e., a decline in juvenile survival over time) in either species. We also found no interspecific differences in age-specific hunting vulnerability, though juveniles were more vulnerable than adults in both species, as expected. Thus, interspecific differences in survival were unrelated to harvest. Lower survival of juvenile Ross's geese may result from natural migration mortality related to smaller body size (e.g., greater susceptibility to inclement weather or predation) compared to juvenile snow geese. Despite lower first-year survival, recruitment by Ross's geese may still be greater than that by snow geese because of earlier sexual maturity, greater breeding propensity, and higher nest success by Ross's geese. © 2012 The Wildlife Society.     

Spring snow goose hunting influences body composition of waterfowl staging in Nebraska

A spring hunt was instituted in North America to reduce abundance of snow geese (Chen caerulescens) by increasing mortality of adults directly, yet disturbance from hunting activities can indirectly influence body condition and ultimately, reproductive success. We estimated effects of hunting disturbance by comparing body composition of snow geese and non-target species, greater white-fronted geese (Anser albifrons) and northern pintails (Anas acuta) collected in portions of south-central Nebraska that were open (eastern Rainwater Basin, ERB) and closed (western Rainwater Basin, WRB; and central Platte River Valley, CPRV) to snow goose hunting during springs 1998 and 1999. Lipid content of 170 snow geese was 25% (57 g) less in areas open to hunting compared to areas closed during hunting season but similar in all areas after hunting was concluded in the ERB. Protein content of snow geese was 3% (14 g) less in the region open to hunting. Greater white-fronted geese had 24% (76 g; n = 129) less lipids in the hunted portion of the study area during hunting season, and this difference persisted after conclusion of hunting season. We found little difference in lipid or protein content of northern pintails in relation to spring hunting. Indirect effects of spring hunting may be considered a collateral benefit regarding efforts to reduce overabundant snow goose populations. Disrupted nutrient storage observed in greater white-fronted geese represents an unintended consequence of spring hunting that has potential to adversely affect reproduction for this and other species of waterbirds staging in the region. © 2012 The Wildlife Society.     

Condition Bias of Decoy-Harvested Light Geese During the Conservation Order

Evidence that decoy harvest techniques primarily remove individuals of poorer body condition is well established in short-lived duck species; however, there is limited support for condition bias in longer-lived waterfowl species, such as geese, where decoy harvest is considered primarily additive because of their high natural survival rates. We evaluated support for the harvest condition bias hypothesis of 2 long-lived waterfowl species, the lesser snow goose (Anser caerulescens caerulescens) and Ross's goose (Anser rossii). We used proximate analysis to quantify lipid and protein content of lesser snow and Ross's geese collected during the Light Goose Conservation Order (LGCO) in 2015 and 2016 during spring migration in Arkansas, Missouri, Nebraska, and South Dakota, USA. In each state, LGCO participants collected birds using traditional decoy techniques and we collected birds from the general population using jump-shooting tactics. Total body lipid content in both lesser snow and Ross's geese varied with age, region of harvest, and harvest type (decoy or jump-shooting). On average, adult lesser snow and Ross's geese harvested over decoys had 60 g and 41 g, respectively, fewer lipids than conspecifics collected using jump-shooting. We observed lower lipid reserves in decoy-shot geese in all 4 states sampled despite general gains in lipid reserves as migration chronology progressed. Our data support that the harvest condition bias extends to longer-lived waterfowl species and during a life-history event (spring migration) in which harvest is not normally observed. In the case of overabundant light geese, the disproportionate harvest of poorer-conditioned lesser snow and Ross's geese may serve as an additional challenge against any realized effects of harvest to reduce the population, in addition to extremely low harvest rates. © 2019 The Wildlife Society.     

Multi-species patterns of avian cholera mortality in Nebraska's Rainwater Basin

Nebraska's Rainwater Basin (RWB) is a key spring migration area for millions of waterfowl and other avian species. Avian cholera has been endemic in the RWB since the 1970s and in some years tens of thousands of waterfowl have died from the disease. We evaluated patterns of avian cholera mortality in waterfowl species using the RWB during the last quarter of the 20th century. Mortality patterns changed between the years before (1976-1988) and coincident with (1989-1999) the dramatic increases in lesser snow goose abundance and mortality. Lesser snow geese (Chen caerulescens caerulescens) have commonly been associated with mortality events in the RWB and are known to carry virulent strains of Pasteurella multocida, the agent causing avian cholera. Lesser snow geese appeared to be the species most affected by avian cholera during 1989-1999; however, mortality in several other waterfowl species was positively correlated with lesser snow goose mortality. Coincident with increased lesser snow goose mortality, spring avian cholera outbreaks were detected earlier and ended earlier compared to 1976-1988. Dense concentrations of lesser snow geese may facilitate intraspecific disease transmission through bird-to-bird contact and wetland contamination. Rates of interspecific avian cholera transmission within the waterfowl community, however, are difficult to determine.     

Does body size influence nest attendance? A comparison of Ross’s geese (Chen rossii) and the larger, sympatric lesser snow geese (C. caerulescens caerulescens)

The body-size hypothesis predicts that nest attendance is positively related to body size among waterfowl and that recess duration is inversely related to body size. Several physiological and behavioral characteristics of Ross’s geese (Chen rossii) suggest that females of this species should maintain high nest attendance despite their relatively small body size. Accordingly, we used 8-mm films to compare the incubation behavior of Ross’s geese to that of the larger, closely-related lesser snow geese (C. caerulescens caerulescens; hereafter, snow geese) nesting sympatrically at Karrak lake, Nunavut, Canada in 1993. We found that nest attendance averaged 99% for both species. Our results offer no support for the body-size hypothesis. We suggest that temperature requirements of embryos in relation to short incubation duration and a low foraging efficiency of females select for high nest attendance in both snow geese and Ross’s geese.     

Distribution of little auk (Alle alle) breeding colonies in Thule District, northwest Greenland

Large areas with hydrocarbon prospects offshore northwest Greenland necessitate seabird studies in this region. The little auk population breeding in Thule District is the largest seabird population in northwest Greenland, as well as the largest known population of this species. In 1994 and 1995 we mapped the distribution of little auk colonies in Thule District during aerial surveys. Most colonies are situated in sloping screes facing the sea, some as far as 11 km from the coast in valleys or facing glaciers. The total horizontal extent of the colonies is about 400 km. Our surveys generally confirm previous and local knowledge, although the information obtained is more detailed. Received: 11 November 1996 / Accepted: 21 September 1997     

The dilemma of where to nest: influence of spring snow cover,food proximity and predator abundance on reproductive success of an arctic-breeding migratory herbivore is dependent on nesting habitat choice

Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice.     

Winter Fidelity and Apparent Survival of Lesser Snow Goose Populations in the Pacific Flyway

Abstract The Beringia region of the Arctic contains 2 colonies of lesser snow geese (Chen caerulescens caerulescens) breeding on Wrangel Island, Russia, and Banks Island, Canada, and wintering in North America. The Wrangel Island population is composed of 2 subpopulations from a sympatric breeding colony but separate wintering areas, whereas the Banks Island population shares a sympatric wintering area in California, USA, with one of the Wrangel Island subpopulations. The Wrangel Island colony represents the last major snow goose population in Russia and has fluctuated considerably since 1970, whereas the Banks Island population has more than doubled. The reasons for these changes are unclear, but hypotheses include independent population demographics (survival and recruitment) and immigration and emigration among breeding or wintering populations. These demographic and movement patterns have important ecological and management implications for understanding goose population structure, harvest of admixed populations, and gene flow among populations with separate breeding or wintering areas. From 1993 to 1996, we neckbanded molting birds at their breeding colonies and resighted birds on the wintering grounds. We used multistate mark-recapture models to evaluate apparent survival rates, resighting rates, winter fidelity, and potential exchange among these populations. We also compared the utility of face stain in Wrangel Island breeding geese as a predictor of their wintering area. Our results showed similar apparent survival rates between subpopulations of Wrangel Island snow geese and lower apparent survival, but higher emigration, for the Banks Island birds. Males had lower apparent survival than females, most likely due to differences in neckband loss. Transition between wintering areas was low (<3%), with equal movement between northern and southern wintering areas for Wrangel Island birds and little evidence of exchange between the Banks and northern Wrangel Island populations. Face staining was an unreliable indicator of wintering area. Our findings suggest that northern and southern Wrangel Island subpopulations should be considered a metapopulation in better understanding and managing Pacific Flyway lesser snow geese. Yet the absence of a strong population connection between Banks Island and Wrangel Island geese suggests that these breeding colonies can be managed as separate but overlapping populations. Additionally, winter population fidelity may be more important in lesser snow geese than in other species, and both breeding and wintering areas are important components of population management for sympatric wintering populations.     

Flyway structure in the circumpolar greater white‐fronted goose

Dispersal and migratory behavior are influential factors in determining how genetic diversity is distributed across the landscape. In migratory species, genetic structure can be promoted via several mechanisms including fidelity to distinct migratory routes. Particularly within North America, waterfowl management units have been delineated according to distinct longitudinal migratory flyways supported by banding data and other direct evidence. The greater white‐fronted goose (Anser albifrons) is a migratory waterfowl species with a largely circumpolar distribution consisting of up to six subspecies roughly corresponding to phenotypic variation. We examined the rangewide population genetic structure of greater white‐fronted geese using mtDNA control region sequence data and microsatellite loci from 23 locales across North America and Eurasia. We found significant differentiation in mtDNA between sampling locales with flyway delineation explaining a significant portion of the observed genetic variation (~12%). This is concordant with band recovery data which shows little interflyway or intercontinental movements. However, microsatellite loci revealed little genetic structure suggesting a panmictic population across most of the Arctic. As with many high‐latitude species, Beringia appears to have played a role in the diversification of this species. A common Beringian origin of North America and Asian populations and a recent divergence could at least partly explain the general lack of structure at nuclear markers. Further, our results do not provide strong support for the various taxonomic proposals for this species except for supporting the distinctness of two isolated breeding populations within Cook Inlet, Alaska (A. a. elgasi) and Greenland (A. a. flavirostris), consistent with their subspecies status.     

Continent-wide tracking to determine migratory connectivity and tropical habitat associations of a declining aerial insectivore

North American birds that feed on flying insects are experiencing steep population declines, particularly long-distance migratory populations in the northern breeding range. We determine, for the first time, the level of migratory connectivity across the range of a songbird using direct tracking of individuals, and test whether declining northern populations have higher exposure to agricultural landscapes at their non-breeding grounds in South America. We used light-level geolocators to track purple martins, Progne subis, originating from North American breeding populations, coast-to-coast (n = 95 individuals). We show that breeding populations of the eastern subspecies, P. s. subis, that are separated by ca. 2000 km, nevertheless have almost completely overlapping non-breeding ranges in Brazil. Most (76%) P. s. subis overwintered in northern Brazil near the Amazon River, not in the agricultural landscape of southern Brazil. Individual non-breeding sites had an average of 91 per cent forest and only 4 per cent agricultural ground cover within a 50 km radius, and birds originating from declining northern breeding populations were not more exposed to agricultural landscapes than stable southern breeding populations. Our results show that differences in wintering location and habitat do not explain recent trends in breeding population declines in this species, and instead northern populations may be constrained in their ability to respond to climate change.     

Decadal changes in vegetation of a subarctic salt marsh used by lesser snow and Canada geese

In the Hudson–James Bay system, grubbing and grazing by lesser snow geese have resulted in severe devegetation of coastal marshes. These changes likely represent an example of an alternative stable state; however, long-term datasets documenting whether revegetation is occurring are scarce. Here, we report results of a 10-year study investigating changes in the state of a degraded salt marsh system on the north coast of Akimiski Island, Nunavut. Four transects were intensively sampled in 1998 and 2008, two within the dense nesting and brood-rearing area of a snow geese colony, one on the colony edge, and one outside it; all of these sites were also used by broods of Canada geese. Key forage species (Puccinellia phryganodes, Festuca rubra, Carex subspathacea) were less common near the colony center than elsewhere; biomass of Puccinellia also tended to be lower in more central areas. Forage species often increased in abundance between samplings, but the magnitude of changes was small. In contrast, non-forage species (Salicornia, Spergularia, Glaux) often reached high abundance within the colony center; some (Salicornia) decreased while others (Spergularia) increased. We argue the degraded state was initiated by foraging damage from an exceptional stopover of 295,000 staging birds in 1972 and that the combined foraging pressure of relatively small numbers of nesting and migrant geese since then, coupled with soil changes, has been sufficient to maintain devegetated areas as a persistent alternative state. Whether or not this state is truly stable, further recovery is likely to be very slow.     

Response of breeding duck pairs to predator reduction in North Dakota

Predator management regularly improves waterfowl nesting success, often beyond levels believed necessary for population maintenance. If recruitment, survival of breeding females, and/or breeding site fidelity is increased on predator-reduced sites, then local breeding populations may increase in subsequent years. During 2005–2008, we annually conducted breeding pair surveys on >600 wetlands at 6 township-sized (93.2 km²) trapped sites and 4 non-trapped sites for the 5 most common upland nesting ducks in eastern North Dakota, USA. For each species, we developed a series of competing regression models that related breeding pair abundance to wetland size, predator management, and upland habitats adjacent to sampled wetlands. In contrast to previous studies, we found limited and equivocal evidence that breeding populations increased following predator management. We discuss multiple potential explanations for this lack of effect and suggest that managers should not assume that increased production as a product of elevated nest success will be compounded over years. © The Wildlife Society, 2013     

Composition of chick meals from one of the main little auk (Alle alle) breeding colonies in Northwest Greenland

During the last decade, increasing information on little auk (Alle alle) biology, ecology and behaviour has been reported. However, only a few of these studies have focused on the breeding population in the Avanersuaq (Thule) district of Northwest Greenland, where 80 % of the global little auk population is estimated to breed. This study reports on the chick diet composition from one of the largest colonies, the Paakitsoq colony, located on the south-eastern margin of the North Water (NOW) Polynya. Results revealed the highest proportion of Calanus hyperboreus, a large lipid-rich copepod, in chick diet reported for any little auk colony. Results confirmed that the cold, highly productive waters of the NOW Polynya are favourable foraging grounds for the little auks during the breeding season. Species diversity within and between the chick meals was low, which probably reflects a high availability of a few preferred prey species. Individual chick meals were generally low in number of prey items and total energy content compared with other published results. This may be explained by a higher feeding frequency or by the samples being collected late in the breeding period (during late chick rearing), when chicks have a reduced growth rate and may require less energy than at earlier developmental stages.     

Strong migratory connectivity and seasonally shifting isotopic niches in geographically separated populations of a long-distance migrating songbird

Whether migratory animals use similar resources during continental-scale movements that characterize their annual cycles is highly relevant to both individual performances and population dynamics. Direct knowledge of the locations and resources used by migrants during non-breeding is generally scarce. Our goal was to estimate migratory connectivity of a small Palaearctic long-distance migrant, the common nightingale Luscinia megarhynchos, and to compare resources used in non-breeding areas with resources used at the breeding grounds. We tracked individuals of three geographically separated populations and characterised their stable isotope niches during breeding and non-breeding over 2 years. Individuals spent the non-breeding period in population-specific clusters from west to central Africa, indicating strong migratory connectivity at the population level. Irrespective of origin, their isotopic niches were surprisingly similar within a particular period, although sites of residence were distant. However, niche characteristics differed markedly between breeding and non-breeding periods, indicating a consistent seasonal isotopic niche shift in the sampled populations. Although nightingales of distinct breeding populations migrated to different non-breeding areas, they chose similar foraging conditions within specific periods. However, nightingales clearly changed resource use between breeding and non-breeding periods, indicating adaptations to changes in food availability.