Pelagic or benthic prey? Combining trophic analyses to infer the diet of a breeding South American seabird, the Red-legged Cormorant (Phalacrocorax gaimardi)

ANNICK MORGENTHALER; ANA MILLONES; PATRICIA GANDINI; ESTEBAN FRERE

EMU

CSIRO PUBLISHING

Año: 2016 vol. 116 p. 360 - 369

0158-4197

The available information about the feeding habits and preferences ofthe Red-legged cormorant (Phalacrocoraxgaimardi) generally considers this near threatened South American cormorantto be a sedentary benthic forager that also incorporates pelagic prey in itsdiet. In order to describe the dietary composition and assess the importance ofcertain prey types (pelagic versus benthic), we studied the diet of this cormorant on the Argentine Atlantic coast during four breeding seasons, using a combinedtechnique of conventional diet assessment (pellets) and stable isotope analysis(SIA). Our results show that the Red-legged cormorant forages mainly on pelagicand demersal-pelagic prey. Results of both techniques showed the main prey tobe the Patagonian Sprat, a small high-energy-content pelagic forage fish, andthe Patagonian Squid, a low-energy-content demersal-pelagic invertebrate. We also found anoverall low prey diversity and important interannual variation for the mainprey types, as well as variation between the different breeding stages. Thisstudy therefore contributes new and unambiguous information about the Red-legged cormorant?s use of trophic resourcesand suggests that the combination of a conventional technique with SIA provides a solid frameworkfor this seabird diet assessment.