DIET OF THE SOUTH POLAR SKUA: COMPARISON OF METHODS OF ANALYSIS

M. MERCEDES SANTOS; MARIANA A. JUÁRES; EMILCE F. ROMBOLÁ; DIEGO GONZALEZ ZEVALLOS; NÉSTOR R. CORIA; C. PATRICK DONCASTER

Portland

Congreso; XXXII SCAR and Open Science; 2012

Studies of the opportunistic diet of South Polar Skuas, Stercorarius maccormicki, can provide valuable information on the status of marine food resources in the high Antarctic. Most studies to date have been based on collection of pellets from breeding colonies or regurgitates of adults and chicks. We report the first study to compare the contents of pellets and regurgitates of South Polar Skuas, produced across years by identified pairs breeding at two colonies on the Antarctic Peninsula. Samples were taken from Potter Peninsula in sympatry with Brown Skuas, Stercorarius antarcticus, and from Cierva Point in allopatry, in order to test the general consensus that penguins feature prominently in the diet at least in the absence of Brown Skuas. We found that penguin remains were much more frequent in samples from the sympatric population than the allopatric population, but only in pellets. Moreover, the high-frequency of penguin feathers was replaced in the pellets of the allopatric population by a high frequency of non-food moss. The rare occurrence of penguins in regurgitates from both sites is consistent with scavenging rather than active predation. The high frequency of feathers in pellets at Potter is consistent with a gut cleansing function similar to that performed by moss, which is abundant only at Cierva. We conclude that evidence for penguins replacing fish in the diet cannot be drawn solely from pellet analysis, and must take account of other non-food functions of ingesting penguin feathers.