Data from: Interannual variation in foraging decisions in chick-rearing black-legged kittiwakes

Long-lived species must balance allocation between reproduction and
self-maintenance, and such a trade-off is expected to affect their
foraging behaviour. A bimodal foraging strategy, where individuals
alternate between long trips for self-maintenance and short trips for
offspring provisioning, may reflect this compromise. Using tracking data
collected over three breeding seasons, we investigated the occurrence of a
bimodal foraging strategy and inter-annual variation in foraging decisions
among black-legged kittiwakes (Rissa tridactyla) breeding in Kongsfjorden,
Svalbard. Kongsfjorden, a glacial fjord with six tidewater glacier fronts,
provides close foraging opportunities to breeding sites. The continental
shelf break outside the fjord offers another foraging area but involves
higher commuting costs. We tested the hypothesis that breeding adults
perform foraging trips outside the fjord for self-maintenance. We
predicted that 1) adults were more likely to undertake foraging trips
outside the fjord when their body condition was low and that 2)
individuals foraging outside the fjord were likelier to improve their body
condition than those foraging within. Our results indicate that kittiwakes
in Kongsfjorden may adopt a bimodal foraging strategy during
chick-rearing, but not every year. Contrary to our first prediction, we
found no evidence that adult body condition affected the probability of
foraging at distant sites. However, adults were more likely to maintain or
improve body condition during outside-fjord foraging trips, supporting the
hypothesis that long-distance trips can be used for self-maintenance.
Overall, our results suggest that bimodal foraging is not a fixed
characteristic of kittiwake foraging behaviour and may be influenced by
environmental conditions.