Evaluating and using stable-isotope analysis to infer diet composition and foraging ecology of Adelie penguins Pygoscelis adeliae

We investigated whether diet composition determined from stable-isotope analysis (SIA) was similar to that determined from stomach content analysis for Adelie penguins Pygoscelis adeliae. We also used SIA to compare diet composition of adults and chicks and to evaluate intra- and inter-annual variations in diet and foraging ecology of adults over 2 consecutive breeding seasons (2001-2002 and 2002-2003) and 3 consecutive moulting seasons (2000-2001 to 2002-2003). Diet determined from SIA closely mirrored that determined from stomach contents at the broad taxonomic level (i.e. fish vs. krill). Diet composition did not differ between adults and chicks, but the more depleted VC values of adult blood suggest that adults may forage for themselves and provide their chicks with food from different locations. Adult delta C-13 signatures varied intra-annually with the most depleted values measured during the arrival period, followed by incubation, guard and then creche. delta N-15 analyses indicated that krill and fish were being consumed prior to arrival at the breeding colonies and during incubation foraging trips, while the primary prey consumed during chick-rearing differed between years. delta(15) N did not vary in the pre-moult periods, with adult diet consisting primarily of krill in all 3 years, but the depleted VC signatures of feathers in 2000-2001 indicated that adults foraged farther from shore in that year. This study demonstrates that SIA is useful for monitoring diet and foraging areas of Adelie penguins at broad resolutions, particularly during periods when it is not possible to use conventional dietary techniques, although penguins may be most vulnerable to impacts such as commercial fishing during these periods as well.