High individual flexibility in the foraging behavior of a marine predator, the common murre

The foraging ecology of breeding seabirds is largely influenced by prey availability and energy demands related to reproduction which, in combination with other factors, can affect resource specialization in space and time. In this study, we combined GPS tracking, dive behavior, and stable isotope ratios of carbon and nitrogen to examine behavioral and dietary flexibility within individuals in a breeding pursuit-diving seabird, the common murre (Uria aalge), on the northeast Newfoundland coast. We examined individual flexibility over 2 years (2016, 2017) during which the timing of arrival and availability of their primary prey, capelin (Mallotus villosus), varied. In both years, we found high within-individual variation in foraging trip and dive characteristics, coupled with low spatial overlap of foraging trips both within and among individuals, indicative of flexible behavior. Concurrently, the isotopic niche of breeding common murres showed a higher degree of dietary consistency, evidenced by similar amounts of variation within and among individuals in stable isotope ratios (δ13C, δ15N). Dietary reconstruction revealed that the proportion of different prey types in the diet varied across individuals, suggesting a degree of dietary flexibility. When capelin (prey) availability was low (in 2017), foraging trips were longer and farther from the colony, maximum dive duration decreased, and the proportion of capelin in the diet decreased. Behavioral flexibility, however, remained similar across both years, regardless of prey availability. Our results suggest that common murres can tolerate and respond to fluctuations in prey availability through flexible foraging strategies. Increased foraging distances during low capelin availability suggest increased energetic costs, and thus, an energetic threshold may be reached above which lower prey availability cannot be tolerated.