Stable isotopes reveal variation by age, sex and locality in the diets and foraging habitats of Southern Giant Petrels breeding in Antarctica and southern Patagonia

A RAYA REY; D ARCHUBY; M POLITO; N CORIA

Victoria, Canada

Conferencia; 1st World Seabird Conference; 2010

We examined the isotopic signatures (δ13C, δ15N) of adult body feathers from southern giant petrels collected at two breeding colonies in Antarctica (Potter Peninsula and Cape Geddes) and one in southern Patagonia (Observatorio Island), as well as in whole blood collected from adults of both sexes at each Antarctic colonies and from chicks at Potter Peninsula. As body feather moult is a continuous process in giant petrels, feathers provide an integrated annual signal of an adult’s diets and foraging habitats. In contrast, the stable isotope values of adult and chick blood are reflective of their diets during the breeding season.  Feathers from the Antarctic colonies showed lower carbon and nitrogen values than those in Patagonia, suggesting that individuals from the Patagonia colony feed predominantly over the continental shelf, while Antarctic birds are likely feeding in Antarctic and Subantarctic waters throughout much of the year. When examining the breeding season (whole blood), males and females differed in their isotopic signature at both Antarctic colonies. This agrees with differences observed at other breeding locations, with females having high δ15N value due to their reliance on marine prey which, in the Antarctic, have higher δ15N values than penguin and seal carrion. Chicks had lower blood isotopic values than both males and females, indicating that adults provision their offspring with a relatively higher amount of carrion that what they consume.  This finding confirms previous work that suggests that chicks are preferentially fed with prey of presumably of higher nutritional value such as carrion.