Age-related prey selectivity and foraging efficiency in Olrog’s Gulls Larus atlanticus feeding on crabs in their non-breeding grounds.

BERÓN MP, GO GARCÍA, T LUPPI & M FAVERO

EMU

CSIRO PUBLISHING

Lugar: Sydney; Año: 2011 vol. 111 p. 172 - 178

0158-4197

Foraging ecology is an essential component of the life history of a species and a good understanding of foraging is especially important for threatened species whose prey populations may be susceptible to damaging anthropogenic processes. This study examines the age-related prey selection and handling efficiency of Olrog’s Gulls foraging during the non-breeding period at Mar Chiquita coastal lagoon, Argentina. Foraging behaviour and diet of Olrog’s Gulls Larus atlanticus was determined by focal observation and contrasted with crab availability in foraging patches. All prey captured by gulls were crabs, with the Burrowing Crab Neohelice granulata being the dominant prey type over the Mud Crab Cyrtograpsus angulatus. Gulls consumed small and medium-sized crabs in higher proportions than those available and consumed more male crabs. Juvenile gulls had longer handling times compared with older birds. Handling times increased with crab size independently of the sex of prey. The handling efficiency in adults was significantly higher than subadults, which in turn was higher than juveniles. These differences in the trophic spectrum between age classes could be attributed to differential foraging skills and social subordination of juvenile gulls. Large crabs might be avoided for other reasons that will need further exploration such as poor digestibility of carapaces, higher risk of injury or kleptoparasitic interactions, among others