Due to climate change, wind patterns are changing in the Southern Ocean. Higher wind speeds enable the wandering albatrosses of the Crozet Islands to travel more rapidly in search of food. This is the conclusion reached by CNRS researchers from the Centre d'Etudes Biologiques de Chizé (CEBC). The phenomenon has modified the distribution of these seabirds and improved their physical condition as well as their breeding success. However, this favorable situation is unlikely to last if these windy areas continue to move southwards. The study was carried out with the support of the French Polar Institute and is the cover story of the 13 January 2012 issue of the journal Science.
Changes in wind patterns are a feature of global warming whose effect on animal populations has been little studied. In the Southern Ocean, these changes have been substantial: westerly winds have increased in intensity and gradually moved southwards over the past thirty years. Some populations of seabirds, such as albatrosses, use the wind as a source of energy when they fly. By considerably reducing their energy expenditure, the wind enables them to fly huge distances, thousands of kilometers from their nests. How have these changes in wind patterns affected albatrosses?
To find the answer to this question, the researchers used several long-term studies carried out in the Crozet Islands, where the demography of the albatross population (annual monitoring of breeding success and survival) has been continuously studied by CEBC for nearly 40 years. Scientists have also been monitoring the birds' size (biometric monitoring) and physical condition (weight). In addition, telemetric monitoring has been performed since 1989, which has enabled researchers to track the movements of over 300 individuals tagged with Argos beacons and GPS. This unique combination of long-term and multi-level monitoring of an animal population has made it possible to go beyond simple correlations between climate change and population parameters, and to better understand the mechanisms involved.
On the basis of telemetry data, the scientists have shown that breeding albatrosses* have increased their flight speed and shifted their foraging territory southwards towards Antarctica in conjunction with changes in wind patterns, which enables the birds to find their food more rapidly. As a result, the duration of foraging expeditions has fallen by over 20%: it is currently 10 days on average, as compared with 13 days in the 1970s. This has resulted in improved breeding success and a spectacular one-kilogram increase in the average weight of the birds. Moreover, the southward shift of the distribution area of the females (previously threatened by subtropical tuna fisheries) has lessened the risk of their accidental capture. The consequences of climate change have so far been favorable to the population of wandering albatrosses in the Crozet Islands. However, climate scenarios predict a continued southward shift of westerly winds, which will gradually move the windy areas favorable to the albatrosses further away from the Crozet Islands.
This study shows the importance of including foraging performance in models that relate climate change to population dynamics. It also shows the crucial effect of changes in wind patterns on migratory species and the importance of taking this parameter into account in future.
* During the breeding season, albatrosses continuously fly back and forth between their breeding colony (mainly in the Crozet islands) and foraging areas located thousands of kilometers from there.
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