Diet, isotopic niche, and spatial distribution of the white-headed petrel (Pterodroma lessonii) at Kerguelen Islands
Résumé
The subantarctic white-headed petrel is unique amongst Procellariidae by its biennial breeding frequency. Its food and feeding ecology is poorly known with limited available bio-logging data and no dietary and isotopic information. Our goal was to detail its prey species and isotopic niche at Kerguelen Islands, which is the most important breeding site in the Indian Ocean. Analysis of stomach contents (n = 56) indicated chicks were fed on fish (68% by mass) and secondarily on cephalopods (26%), whilst crustaceans were minor dietary components. Mesopelagic fishes were the main prey, with myctophids and melamphaids being the most important fish family in terms of both abundance (50% and 15% of the fish, respectively) and diversity (10 and three species). Prey distribution indicated that petrels foraged primarily in subantarctic waters and secondarily further south to feed their chicks, which is corroborated by the lower blood δ13C values of fledglings (n = 10) than incubating adults (n = 9). Body feather δ13C values (n = 45) indicate that adult white-headed petrels moulted over different latitudinal habitats, from the subtropics to Antarctica where δ15N values showed they fed on low trophic-level prey (most likely Antarctic krill). Indeed, three geolocator-tracked birds ranged widely, from the mid-Atlantic (18° W) to the eastern Indian Ocean (110° E) and from the warmer Subtropical Zone (19% of the locations), across the Subantarctic Zone (58%) to the colder Antarctic Zone (23%). Neither fishery-related items nor plastic debris were found in chick food samples, thus indicating no significant interactions with human activities, which is a key positive issue for the conservation of white-headed petrels.