Does snow melt timing affect nesting interspecific competition between two goose species?

Abstract Global climate change can alter the timing of migration for birds, and these temporal shifts can differ across species. There is little knowledge about whether these timing shifts could alter interspecific competition, with effects on reproductive success or interspecific interactions. Cackling geese ( Branta hutchinsii ) and Atlantic brant ( Branta bernicla hrota ) share similar coastal nesting habitat and may exhibit pre‐emptive interference competition for nest sites. Thus, in early snow melt years when cackling geese can initiate nests 2 weeks sooner than brant, they may have a competitive advantage in finding optimal nesting sites that provide protection from Arctic foxes ( Vulpes lagopus ). In late melt years when both species initiate nests within a few days of each other, competitive advantages are less certain. Using a natural experiment driven by strong interannual variation in snow melt timing (early snow melt year of 2014 and the late snow melt year of 2015) on Southampton Island, Nunavut, Canada, we assessed whether snow melt timing affected nest site characteristics, brant behaviors, and nest success. Behavioral scans revealed that brant males and females altered their behavior between years that differed in cackling goose nest density, suggesting indirect exploitative competition for food resources. Apparent nest success varied between species and years, with brant nest success increasing in the late snow melt year of 2015. Our top model indicated that water levels surrounding nest sites limited arctic fox depredation, and brant nest success was higher in the years with later snow melt, which also had higher water levels during nesting. This study highlights the importance of considering interspecific competition in understanding the impacts of climate change on Arctic breeding bird populations.