Goose persistence in fall strongly influences Arctic fox diet, but not reproductive success, in the southern Arctic

Food availability is the primary limitation for terrestrial Arctic predators, many of which rely on rodents that fluctuate in abundance over a 3-5-year period. During rodent scarcity, predators such as Arctic foxes (Vulpes lagopus) consume alternative prey, such as migratory birds, which are plentiful during summer. In most of the Arctic these birds return south by August, but in northern Manitoba, near the southern edge of the Arctic fox distribution, large numbers of lesser snow geese (Chen caerulescens caerulescens) and Canada geese (Branta canadensis interior) persist into October. This extended availability of geese late into fall may reduce the dependence of Arctic foxes on rodents. We used stable isotope and faecal analyses to reconstruct the Arctic fox fall and winter diet and related the most probable contributions of lemmings, goose eggs and juvenile geese with changes in prey availability and fox reproduction. Geese were a potentially important component of the fall diet for Arctic foxes, especially in years with high goose productivity, but rodents were the main component of the diet in late winter, even though rodents were scarce each summer (2010-2013). Furthermore, rodent density had a greater influence on Arctic fox reproduction, which was correlated with the subsequent winter harvest, than any other variable examined. Although geese were important fall prey for Arctic foxes at the southern edge of their distribution, they did not buffer declines in availability of rodents, which were the primary prey in April when food availability is critical for Arctic fox reproduction.