A recent long-term study reports on the development of the three brush-tailed penguins: Adélie, Chinstrap and Gentoo penguins on the South Orkney Islands. The study compares their situation with the population development around the Antarctic Peninsula. The scientists can look back on a continuous census data set of 38 years, since 1978/79. Previously only sporadic counts were done. While the populations of Adélie and Gentoo penguins were subject to regular fluctuations, the number of Chinstrap penguins decreased steadily. However, the Adélie penguin colonies were also decreasing. The Gentoo penguins did relatively well over the years, their numbers were increasing – a trend that is also observed at the Antarctic Peninsula. The researchers explain the observed fluctuations with a lively exchange of nesting birds between colonies of the archipelago. At present, Adélie, Chinstrap and Gentoo penguin populations at the South Orkneys are estimated to be about 200,000, 600,000, and 5000-10,000 breeding pairs, respectively.
Today it is assumed that a change in population size can be a good indicator of changes in the ecosystem. This is researched in a number of krill-eating species, e. g. also the brush-tailed penguins. The Commission for the conservation of Antarctic marine living resources (CCAMLR) uses this data to monitor the marine Ecosystem. With that they can set catch limits for the krill and fish fisheries.
All three species are breeding together on Signy Island, South Orkney Islands. While the breeding success of all species is equally good or bad over the years in the observed period, the population development is different. Since the beginning of the continuous census Adélie penguins decreased by 42% and Chinstrap penguins by 68%. In the same period, the originally much smaller Gentoo penguin population increased by 255%! Historical data show a completely different trend between 1947 and 1978: the numbers of the first two species increased enormously during this early period.
According to some scientists, the population development seems to be correlated to the regional decline in sea ice extent and the long-term warming of the region. However, the researchers of the present study are looking a bit deeper into the context, because ice-loving Adélie penguins and ice-avoiding chinstrap penguins are subject to the same decline. They point out that the survival rate of the young penguins during their first winter, the access to krill stocks and the increase in fur seal numbers and whales as food competitors in the area, also seem to play a major role. Between 1977 and 1994, the number of fur seals increased tenfold at Signy Island.
In order to gain a better understanding for the decline of one species and the success of another, researchers have to look into the dynamics of the system even deeper. Their long-term data of the last decades and data from other field of subjects are important components for future models and understanding of the processes observed.