Seabird research at Cape Shirreff, Livingston Island, Antarctica, 2003–2004

The seventh consecutive season of data collection at Cape Shirreff has enabled us to examine trends in penguin populations, as well as inter-annual variation in reproductive parameters, penguin diet, and foraging behaviour. The chinstrap breeding population at Cape Shirreff has continued to decline over the past five years, and is at its lowest size in the past seven years of study. While the gentoo breeding population increased slightly from last year, it is at its second lowest size in the past seven years. Chinstrap fledging success was higher during the 2003-04 breeding season than in the previous season, but lower than the average for the past seven years. Gentoo fledging success in 2003-04 was greater than in 2002-03, and was either similar to or greater than the seven-year mean, depending on methodology used. Fledging weights of both species increased from last year, but were below the eight-year mean for this parameter. Total chick meal mass was larger in both species compared to the past seven years study. Chinstrap penguin diet contained more fish than in other years on average, while gentoo diets contained less fish. The majority of the krill in chinstrap diets were in the 36-45 mm range; the majority of krill in gentoo diets were in the 41-55 mm range. This is the first season where the two penguin species have selected different sized krill during the chick-rearing period. Foraging trip durations during the chick phase were longer than during the 2002-03 breeding season. The interpretation of the foraging trip behaviour may be clarified when we finish our analyses of the PTT derived, at sea foraging locations used by chinstrap and gentoo penguins during this period.