Foraging by experienced and inexperienced Cory’s shearwater along a 3-year period of ameliorating foraging conditions

Experience is believed to be an important factor determining the foraging success of animals, but there is limited knowledge on how foraging tactics differ among individuals, and on how individuals develop efficient foraging strategies. Pelagic seabirds are some of the longest living organisms, and in several species, breeding is deferred far beyond their physical maturity. The complex foraging skills needed to successfully rear a young is considered the most likely explanation for this life trait, making seabirds particularly interesting for the investigation of how foraging skills differ and develop through their life span. In our study, the spatial distribution and foraging tactics of experienced and inexperienced males of a Procellariiform seabird species, the Cory’s shearwater (Calonectris borealis) breeding on the Portuguese continental shelf, were compared along three consecutive breeding seasons with ameliorating environmental conditions (from 2010 towards 2012). Kernel overlaps of foraging areas and habitat modelling demonstrated that while experienced males showed high fidelity to shallow feeding grounds, inexperienced birds were more explorative and relied more on less-productive pelagic areas. Our results seem to support the prediction that differences between experienced and inexperienced individuals are enhanced by food scarcity. In fact, there was a higher spatial, trophic and behavioural segregation between both groups when environmental conditions were poor, which progressively diminished with improving environmental conditions. Still, we cannot rule out the fact that inexperienced birds might be gaining experience with each breeding season and thus honing their foraging skills towards those of experienced individuals.