Abstract
Measurements of the size of Adélie penguin (Pygoscelis adeliae) colonies of the southern Ross Sea are among the longest biologic time series in the Antarctic. We present an assessment of recent annual variation and trends in abundance and growth rates of these colonies, adding to the published record not updated for more than two decades. High angle oblique aerial photographic surveys of colonies were acquired and penguins counted for the breeding seasons 1981–2012. In the last four years the numbers of Adélie penguins in the Ross and Beaufort Island colonies (southern Ross Sea metapopulation) reached their highest levels since aerial counts began in 1981. Results indicated that 855,625 pairs of Adélie penguins established breeding territories in the western Ross Sea, with just over a quarter (28%) of those in the southern portion, constituting a semi-isolated metapopulation (three colonies on Ross Island, one on nearby Beaufort Island). The southern population had a negative per capita growth rate of −0.019 during 1981–2000, followed by a positive per capita growth rate of 0.067 for 2001–2012. Colony growth rates for this metapopulation showed striking synchrony through time, indicating that large-scale factors influenced their annual growth. In contrast to the increased colony sizes in the southern population, the patterns of change among colonies of the northern Ross Sea were difficult to characterize. Trends were similar to southern colonies until the mid-1990s, after which the signal was lost owing to significantly reduced frequency of surveys. Both climate factors and recovery of whale populations likely played roles in the trends among southern colonies until 2000, after which depletion of another trophic competitor, the Antarctic toothfish (Dissostichus mawsoni), may explain the sharp increasing trend evident since then.
Highlights
The underlying factors most likely to limit the abundance of breeding seabirds in a region are prey or nesting space availability [1]
Spatio-temporal variation in climatic variables resulting from phenomena such as long-term climate change, or shorterterm decadal atmospheric variation, i.e. factors related to the Southern Oscillation and Antarctic Oscillation
Counts of Adelie penguin breeding pairs in the northern Victoria Land population over the last 20 years have been infrequent so the variation, quite similar across colonies, needs to be interpreted with caution
Summary
The underlying factors most likely to limit the abundance of breeding seabirds in a region are prey or nesting space availability [1] These effects are manifest in key demographic rates such as age-specific survival, dispersal and proportion breeding. This is especially so for central-place foragers like Antarctica’s ‘‘true’’ pack-ice penguins, Emperor (Aptenodytes forsteri) and Adelie (Pygoscelis adeliae) penguins, which breed gregariously in large colonies [2]. The inability of these penguins to forage across vast distances means that they are influenced to a greater degree than volant species (e.g. albatrosses Diomedea spp.) by the local habitat and resources and by changes in conditions and prey stocks. Spatio-temporal variation in climatic variables resulting from phenomena such as long-term climate change, or shorterterm decadal atmospheric variation, i.e. factors related to the Southern Oscillation and Antarctic Oscillation
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