Antarctic seabirds start breeding later
Eight of the nine seabird species breeding in Antarctica have had delayed arrival to their traditional nesting grounds over the past 55 years. On average, their arrival was delayed by nine days and the time when they laid their eggs by two days. This trend is completely in reverse to that observed in the Northern Hemisphere, where spring arrival and bird nesting times have steadily advanced over the past several decades.
The triggers for this development are probably the spatial reduction in the sea ice cover, the extent of which in the region has shrunk by 12 to 20 percent since records began in 1950, and the extension of the sea ice season by 40 days, as the two ornithologists Christophe Barbraud say and Henri Weimerskirch from the Center National de la Recherche Scientifique in Villiers en Bois. According to evaluations of the data collected since 1950 in the vicinity of the French research station Dumont d'Urville in Adélie Land, only the Antarctic Skuas (Catharacta maccormicki) moved their breeding start forward by almost four days. But unlike the other seabirds, these feed on the eggs and young of Adélie penguins.
All other species depend on fish, crustaceans (primarily krill) and squid, the abundance of which has declined significantly due to the prolonged sea ice season and reduced extent. While the ice generally blocks access to breeding areas, it takes longer for the animals to acquire sufficient physical reserves for breeding. According to the two scientists, however, these two aspects can only partially explain the delayed start of incubation, as they caused at most a quarter of the observed variance. Therefore, other factors must also play a role that are unknown to the researchers so far.
The seabirds show a certain adaptability, however, since the late arrival does not delay the start of breeding to the same extent. Nevertheless, Barbraud and Weimerskirch fear serious effects on the population of the animals should the climate changes currently observed in the Antarctic continue to have an increasingly negative impact on the ecological conditions of the region in the future.
