Trophic segregation between sexes in the Black Skimmer revealed through the analysis of stable isotopes.

MARIANO-JELICICH R, F BOTTO, M FAVERO, P MARTINETTO & O IRIBARNE.

MARINE BIOLOGY

SPRINGER

Año: 2008 vol. 155 p. 443 - 450

0025-3162

Most studies of seabird diet have relied upon conventional methods widely used for identifying prey taxa like the examination of stomach contents and the analysis of pellets. Recently the analysis of stable isotopes has been described as a powerful tool to study trophic ecology in animals, and particularly with seabirds they have been reported as good trophic indicators. In this study stable isotope techniques were used to investigate intraspecific segregation in diet and trophic habits of the Black Skimmer (Rynchops niger intercedens). These results were finally compared with contemporary data on trophic composition obtained by conventional methodologies. Samplings were done between October 2003 and May 2005 at Mar Chiquita Coastal Lagoon, Argentina. Blood samples taken from birds captured with mist-nets during their non-breeding season were analyzed. The isotopic signatures of skimmers showed a diet mainly composed of marine with some degree of estuarine intake of fish species. When comparing sexes, males showed an enrichment in 15N compared to female, while no differences were observed in 13C. Differences in the relative composition of prey in the diet of male and female skimmers were found when the mixing model was applied. The results show the existence of an intraspecific trophic segregation in the Black Skimmer during the non-breeding season. This segregation could be partially explained by the morphological and anatomical differences between sexes of this species. Moreover, these results show how the analysis of stable isotopes reinforces and complements the information about trophic spectrum in top predators done following the classic methodologies