Seabird research at Cape Shirreff, Livingston Island, Antarctica, 2005/06

Our ninth complete consecutive season of seabird research at Cape Shirreff allowed us to assess trends in penguin population size, as well as inter-annual variation in reproductive success, diet and foraging behaviour. The gentoo penguin breeding population declined marginally from the previous season and is the third lowest population size in the 10 years of census data. The chinstrap penguin breeding population has been declining for the Past eight years and is at its lowest size in the 10 years of study. Gentoo penguin fledging Success was the highest recorded in all the years of study. The fledging success for chinstrap penguins was noticeably higher during the 2005/06 season than in the previous season and was slightly higher than the previous eight year mean. Gentoo penguin fledge weights for this season was the highest recorded in all the years of study. Chinstrap penguins fledge weights increased slightly from the 2004-05 season and were close to the previous eight year mean. Both gentoo and chinstrap penguin diets were comprised mainly of adult female Antarctic krill, the majority of which were 51-55mm in length. This is a continuation of a four year trend with increasing proportions of female krill and increasingly larger krill. Chinstrap penguin total chick meal mass was lower than almost all of the previous eight years of diet sampling; however, foraging trip durations were shorter than during the 2004/05 season. This may indicate that the provisioning rate of chicks by adults may have been higher, which would account for this difference. This interpretation may be aided by analysis of foraging location and diving behaviour data to be done at a later date.