EFFECTS OF ABUNDANT SNOW AND ROSS’S GEESE ON ARCTIC ECOSYSTEM STRUCTURE: PLANTS, BIRDS, AND RODENTS

Migratory animals link and often have profound impacts on geographically distant ecosystems through trophic interactions and transport of nutrients, energy, toxins, parasites and pathogens. Moreover, when seasonally linked ecosystems differ in carrying capacity of migrant species, detrimental effects to biodiversity through trophic cascades can occur in ecosystems with lower carrying capacity. Access to agricultural production has increased carrying capacity of lesser snow (Anser caerulescens caerulescens) and Ross’s geese (Anser rossii, collectively, ‘light geese’) in southern agricultural landscapes where these species winter and stage during migration to and from northern breeding regions. Rapid population growth in response to increased carrying capacity during fall, winter, and spring has caused trophic cascades in less productive subarctic and arctic ecosystems during summer. I investigated changes to plant community structure in direct response to foraging and nesting by abundant and highly concentrated light geese within the Queen Maud Gulf (Ahiak) Migratory Bird Sanctuary, Nunavut, Canada, with particular reference to Karrak Lake, one of the largest nesting goose colonies in the world. I further studied indirect impacts of vegetation change on aspects of sympatric vertebrate response, including resident brown lemmings and ptarmigan, and migratory shorebirds and passerines. Foraging by light geese created spatially heterogeneous landscapes composed of lightly and intensely foraged grazing lawns in the brood-rearing and molting region north of Karrak Lake, within the pre-existing mosaic created by variation in topography, moisture, and soil properties created by geomorphic processes. Although foraging light geese nearly depleted aboveground plant biomass in some areas in the Sanctuary, belowground biomass was largely intact and thus, plant communities have strong potential for aboveground regeneration. Nesting and foraging geese severely reduced aboveground plant biomass within the nesting colony at Karrak Lake. Colonizing plant species established on bare sediment or peat exposed by previous vegetation removal by geese, resulting in shifts in species composition of plant communities. High occupancy by nesting light geese resulted in transition of lowland communities dominated by grasses and sedges (collectively, ‘graminoids’), Sphagnum spp., and willows (Salix spp.) to those comprised of exposed peat, birch (Betula glandulosa), non-Sphagnum mosses, marsh ragwort (Tephroseris palustris), and mare’s tail (Hippuris vulgaris). Community changes were less apparent in upland regions that are naturally less vegetated even in the absence of geese, but fruticose lichens, crowberry (Empetrum nigrum) and white heather (Cassiope tetragona) dominated undisturbed plant communities whereas crustose lichens and bearberry (Arctostaphylos spp.) comprised disturbed communities. Reduction of plant biomass and community shifts from graminoid dominance to those with high proportions of exposed peat and birch had negative effects on abundance of brown lemmings and occupancy by graminoid-specialist shorebirds; however, some open-nesting and generalist cover-nesting avian species showed neutral or positive responses to establishment of birch in altered habitats. Intact graminoid communities are important to ecosystem structure and function and population health of many resident and migratory arctic vertebrates. However, light geese often nest in localized, dense aggregations, and thus negative impacts on sympatric species may be spatially limited and confined to large nesting colonies and severely altered brood-rearing and molting regions. Moreover, altered upland and lowland habitats remained largely vegetated in the Sanctuary, contrasting sharply with altered coastal marshes in subarctic regions

Breeding Biology of King Eiders Nesting on Karrak Lake, Northwest Territories

We studied various aspects of the breeding biology of king eiders (Somateria spectabilis) nesting at Karrak Lake, south of Queen Maud Gulf in the central Canadian Arctic. We found 41 nests distributed among 10 islands in Karrak Lake; to our knowledge, this represents the largest number of king eider nests studied at one site. We suspect that island nesting by king eiders is more common than has been previously reported. King eiders favoured mid-sized islands (0.002-0.081 km²) over very small (less than 0.002 km²) or very large (greater than 0.081 km²) islands. Mean clutch size was 5.4 ±1.7 (SD) eggs. Apparent nest success was 69.4% with a composite Mayfield estimate of nest success over egg laying and incubation of 48.7% (95% CI: 47.4-50.0%). Nest success was uncorrelated with date of nest initiation or island size, but eiders nesting on islands farther from the mainland had greater success than those nesting on islands closer to the mainland. Additionally, nest success was greater on islands with more nesting eiders and on islands with nesting arctic terns (Sterna paradisaea).On a étudié divers aspects de la biologie reproductive de l'eider à tête grise (Somateria spectabilis) nichant au lac Karrak, qui se trouve au sud du golfe de la Reine-Maud, au centre de l'Arctique canadien. On y a trouvé 41 nids répartis sur 10 îles situées dans le lac Karrak; à notre connaissance, cela représente le plus grand nombre de nids d'eiders à tête grise faisant l'objet d'une étude sur un seul site. On soupçonne que l'eider à tête grise niche plus couramment dans des îles qu'on ne l'avait rapporté précédemment. Les individus préféraient les îles de taille moyenne (0,002 à 0,081 km²) aux îles très petites (moins de 0,002 km²) ou très grandes (plus de 0,081 km²). La taille moyenne des couvées était de 5,4 oeufs, avec un écart-type de 1,7. Le taux d'éclosion apparente était de 69,4 p.cent, avec une estimation composée de Mayfield de 48,7 p.cent (intervalle de confiance au seuil de 95 p.cent: 47,4 à 50,0 p.cent) pour le succès de la couvaison par rapport à celui de la ponte et de l'incubation. Le succès de la couvaison n'était pas corrélé à la date du début de la nidification ou à la taille de l'île, mais les eiders nichant sur les îles les plus éloignées du continent réussissaient mieux que ceux nichant sur les îles plus proches du continent. En outre, le succès de la nidification était plus grand sur les îles où nichaient plus d'eiders et sur celles où nichaient aussi des sternes arctiques (Sterna paradisaea)

Vegetation Correlates of the History and Density of Nesting by Ross’s Geese and Lesser Snow Geese at Karrak Lake, Nunavut

Growth in populations of Ross’s geese (Chen rossii) and lesser snow geese (C. caerulescens) has led to concerns about destructive grazing of Arctic ecosystems. We estimated the extent and composition of plant communities at Karrak Lake, Nunavut, where populations of both goose species have grown geometrically over the past three decades. Proportion of land covered by vegetation was lower in areas where geese had nested for more than 20 years than in areas with no previous nesting history. Vegetative cover also declined with increasing nest density of both species. Species richness and diversity of vegetation was higher in more recently colonized areas of nesting than in areas with over 20 years of goose nesting. Exposed mineral substrate, exposed peat, and Senecio congestus were more prevalent in areas with a 10-year or longer history of goose nesting than in areas with less than 10 years of nesting. These patterns confirm that increasing numbers of nesting Ross’s geese and lesser snow geese have altered the spatial distribution of vegetation surrounding Karrak Lake and reduced the species richness of local plant communities.La croissance des populations d’oie de Ross (Chen rossii) et de petite oie des neiges (C. caerulescens) engendre des préoccupations en matière de broutage destructif des écosystèmes de l’Arctique. Nous avons estimé l’ampleur et la composition des peuplements végétaux du lac Karrak, au Nunavut, où les populations de ces deux espèces d’oies ont augmenté de manière géométrique au cours des trois dernières décennies. La proportion de terre couverte par la végétation était moins élevée dans les régions où les oies avaient niché pendant plus de 20 ans que dans les régions où ces oies n’avaient jamais niché. Par ailleurs, la couverture végétale affichait une baisse là où la densité de nidification des deux espèces augmentait. La richesse des espèces et la diversité de la végétation étaient plus grandes dans les lieux de nidification colonisés plus récemment que dans les lieux de nidification colonisés il y a une vingtaine d’années. Les substrats de minéraux à découvert, la tourbe à découvert et le Senecio congestus se voyaient plus souvent dans les régions où les oies avaient niché pendant dix ans ou plus que dans les régions où les oies avaient niché pendant moins de dix ans. Ces tendances confirment que les populations croissantes d’oies de Ross et de petites oies des neiges ont altéré la répartition spatiale de la végétation entourant le lac Karrak, en plus de réduire la richesse des espèces et des peuplements végétaux des environs

Variation in migration behaviors used by Arctic Terns (Sterna paradisaea) breeding across a wide latitudinal gradient

Arctic Terns (Sterna paradisaea) share a few routes to undertake the longest annual migrations of any organism. To understand how the wide spatial range of their breeding colonies may affect their migration strategies (e.g., departure date), we tracked 53 terns from five North American colonies distributed across 30° of latitude and 90° of longitude. While birds from all colonies arrived in Antarctic waters at a similar time, terns nesting in the Arctic colonies migrated back north more slowly and arrived to their breeding grounds later than those nesting in the colony farther south. Arrival dates in Antarctic waters coincided with the start of favorable foraging conditions (i.e., increased ocean productivity), and similarly arrival dates at breeding colonies coincided with the start of local favorable breeding conditions (i.e., disappearance of snow and ice). Larger birds followed a more direct southbound migration route than smaller birds. On both southbound and northbound migrations, daily distances traveled declined as time spent in contact with the ocean increased, suggesting a trade-off between resting/foraging and traveling. There was more unexplained variation in behavior among individuals than among colonies, and one individual had a distinctive stop around Brazil. Terns nesting in the Arctic have a narrow time window for breeding that will likely increase with continuing declines in sea ice and snow. Departing Arctic Terns likely have few clues about the environmental conditions they will encounter on arrival, and their response to environmental changes at both poles may be assisted by large individual variation in migration strategy

UNICORNS: Uveitis in childhood prospective national cohort study protocol [version 1; peer review: 1 approved, 1 approved with reservations]

Background: Childhood uveitis is a rare inflammatory eye disease which is typically chronic, relapsing-remitting in nature, with an uncertain aetiology (idiopathic). Visual loss occurs due to structural damage caused by uncontrolled inflammation. Understanding of the determinants of long term outcome is lacking, including the predictors of therapeutic response or how to define disease control. Aims: To describe disease natural history and outcomes amongst a nationally representative group of children with non-infectious uveitis, describe the impact of disease course on quality of life for both child and family, and identify determinants of adverse visual, structural and developmental outcomes. Methods: UNICORNS is a prospective longitudinal multicentre cohort study of children newly diagnosed with uveitis about whom a core minimum clinical dataset will be collected systematically. Participants and their families will also complete patient-reported outcome measures annually from recruitment. The association of patient (child- and treatment- dependent) characteristics with outcome will be investigated using logistic and ordinal regression models which incorporate adjustment for within-child correspondence between eyes for those with bilateral disease and repeated outcomes measurement. Discussion: Through this population based, prospective longitudinal study of childhood uveitis, we will describe the characteristics of childhood onset disease. Early (1-2 years following diagnosis) outcomes will be described in the first instance, and through the creation of a national inception cohort, longer term studies will be enabled of outcome for affected children and families

Reduction in biomass of freshwater arctic vegetation by foraging and nesting hyperabundant herbivores shows recovery

Abstract Arctic‐nesting geese are specialist herbivores of grasses and sedges (collectively, graminoids). Under moderate grazing pressure, these migratory herbivores can create and maintain arctic grazing lawns with high nutritional content and low aboveground biomass. Nutrient and energy subsidies from southern agricultural landscapes during winter have improved survival among populations of Ross's (Anser rossii) and lesser snow geese (Anser caerulescens caerulescens), leading to marked population growth. Resulting goose hyperabundance has raised conservation concern for resilience of arctic ecosystems to withstand cumulative and intense pressures of herbivory and nest construction. We used both design‐based (experimental herbivore exclosures) and model‐based methods to investigate changes to plant community structure in direct response to foraging and nesting by these species within the Queen Maud Gulf (Ahiak) Migratory Bird Sanctuary, Nunavut, Canada. Annual nest construction and foraging by up to ~1.3 million geese at a large colony at Karrak Lake markedly reduced aboveground biomass of forage (graminoids) and non‐forage (foliose and fruticose lichens) vegetation, with spatial variation in reduction associated with intensity of use by geese. Within vast brood‐rearing regions, foraging reduced above‐ and belowground plant biomass of lowland plant communities by 61% and 29%, respectively, between 1994 (when herbivore exclosures were established) and 2017. In addition to landscape diversity associated with abiotic properties created by geomorphic processes, long‐term herbivory by geese further increased spatial heterogeneity in vegetation at the landscape scale. Although foraging geese nearly completely depleted aboveground plant biomass in some parts of their brood‐rearing areas, belowground biomass was largely conserved, and thus, plant communities had strong potential for aboveground regeneration. We propose that the effects of high‐density nesting and foraging by Ross's and lesser snow geese in the central Canadian Arctic, while extensive, are ephemeral and prone to reversion following cessation of grazing and nesting pressure, such as that afforded by shifts in herbivore distribution or local population decline

Data from: Density‐dependent and phenological mismatch effects on growth and survival in lesser snow and Ross's goslings

Strong seasonality of high‐latitude environments imposes temporal constraints on forage availability and quality for keystone herbivores in terrestrial arctic ecosystems, including hyper‐abundant colonial geese. Changes in food quality due to intraspecific competition, or food availability relative to the breeding phenology of birds, may have consequences for growth and survival of young. We used long‐term data (1993‐2014) from the Karrak Lake nesting colony in the Canadian central arctic to study relative roles of density and phenological mismatch (i.e. days between seasonal peaks in vegetation quality and hatching) as drivers of annual variations in gosling survival among lesser snow (Anser caerulescens caerulescens) and Ross's geese (A. rossii). Survival of Ross's goslings was consistently higher compared to snow geese. For both species, annual gosling survival was greatest when phenological mismatch was minimal and when nesting population size was low. We also examined gosling structural size (1999‐2014) in relation to density and mismatch hypotheses to understand whether changes in survival were preceded by a parallel response in growth stemming from a density‐dependent effect on annual forage conditions. After controlling for sex, age and random effects of capture group and year × species, structural size of both snow and Ross's goslings was reduced in years when phenological mismatch was greater. However, there was no significant evidence that body size of goslings was negatively related to breeding population size at the colony. Our results lend support to the notion that both broad‐scale changes in seasonality from observed and predicted warming in the arctic and, to a lesser extent, density‐dependence on brood‐rearing areas may result in changes to offspring quality or survival, with implications for population recruitmen