Both sexes of central-place-foraging seabirds usually share the task of incubation and alternate fasting bouts on the egg with foraging trips at sea. Because foraging strategies during incubation are poorly known, compared with strategies during chick rearing, we examined the foraging behavior of incubating Little Penguins (Eudyptula minor), together with nest-attendance behavior. The duration of foraging trips varied greatly (1–9 days). Birds with lower initial body condition made longer foraging trips, and the increase in body condition after multi-day trips was higher than that after single-day trips. During trips of >1 day, females dove more times each day but total underwater time did not differ between the sexes. By contrast, during one-day trips, foraging males made as many dives as females and spent more time underwater. Birds making longer trips spent more time diving on the second day than on the first day. The proportion of dives in which prey was encountered was lower during single-day than multi-day trips; during the latter, the proportion was lower on the first day than on the second and subsequent days. Body condition of Little Penguins seems to be an important factor influencing trip duration during incubation. Little Penguins apparently undergo long trips to target more profitable, distant prey patches. Incubating Little Penguins benefit from combining short and long trips at sea to optimize both reproduction and survival.
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Vol. 125 • No. 3