Insights into diet and foraging behaviour of imperial shags (Phalacrocorax atriceps) breeding at Staten Island and Becassess Islands, Tierra del Fuego, Argentina.

HARRIS S; SAENZ SAMANIEGO R; RAYA REY A

WILSON JOURNAL OF ORNITHOLOGY

WILSON ORNITHOLOGICAL SOC

Año: 2016 vol. 128

1559-4491

Diet and behavior are essential aspects of ecological studies, and are even more informative if both aspectsare studied together. We collected samples of feathers (n ¼ 10 of unknown sex at Becasses Island in 2013) and of bothfeathers and blood at Staten Island (n¼5 males and n¼5 females in 2011 and in 2013) from Imperial shags (Phalacrocoraxatriceps). In addition, GPS devices were deployed on two individuals at each location that allowed us to record one or twoforaging trips each. Stable isotope composition of carbon and nitrogen in blood differed amongst years and between sexes,albeit marginally within each year at Staten Island. Feather stable isotopes of carbon and nitrogen did not differ amongstsexes or years at Staten Island and between Staten and Becasses islands to show individuals did not have significantlydifferent diets amongst locations during pre-molt. Foraging behavior parameters did not differ between individuals as they allsearched in shallow waters and close to shore. Individuals flew to their feeding grounds and searched intensively at thefurthest point reached by diving interspersed with floating on the surface. These results show individuals feed on similar prey,at least during pre-molt, and would seem to behave in a similar way at both locations while breeding, though sample size istoo small to generalize on their behavior. The differences in isotopic compositions amongst years for Staten Island could beshowing the fluctuations that occur among seasons in the isotopic signatures of prey, and in consequence, in seabirds overtime.