Experimental and field evidence indicate that islet-nesting tundra birds experience reduced nest predation and benefit indirectly from high snow goose densities

Abstract

Landscape features can shape the occurrence and strength of predator-prey interactions by influencing predation risk and prey distribution. In the High Arctic, some bird species select nesting sites with physical features that limit the access by their main terrestrial predator, the arctic fox, though these features do not always provide full protection. We investigated how nest microhabitat characteristics and prey availability modulate nest survival in tundra birds that select pond and lake islets as breeding sites. Over four summers, we analyzed the survival of 132 cackling goose and 55 glaucous gull nests located on islets or on pond and lake shores within a 150 km2 area occupied by a snow goose colony on Bylot Island, Nunavut, Canada. We also analyzed survival of 537 artificial nests deployed over three summers. We found that islets act as partial prey refuges, with higher nest survival rates on islets than on pond and lake shores. Nest survival generally increased with islet distance from shore, but we found little evidence of this effect for cackling geese and glaucous gulls, which avoided nesting on islets near shore. Moreover, water depth surrounding islets had little to no influence for any nest type. Nest mortality was much higher in a year with relatively low snow goose nest density, suggesting a short-term positive indirect effect of this colonial nesting bird on species nesting on islets. Since the arctic fox was virtually the sole predator of artificial nests, our findings indicate that annual variation in nest survival on islets were driven by a shift in fox foraging behavior in response to changes in prey availability across the landscape. Our study, which integrates multi-year monitoring and field experiments, highlights the interplay between microhabitat selection and predator-multi-prey dynamics in the arctic tundra.