Factors controlling the distribution of seabirds: Winter-summer heterogeneity in the distribution of adélie penguin populations

Recent and historical data on the distribution of Adelie Penguins in the western Antarctic Peninsula region were analyzed to examine and detect patterns and causes of heterogeneity, and to relate these to long-term JXlPuJation changes. Adelie Penguins are onc of the dominant componensts of the region's seabird community in terms of biomass, but not in numerical abundance. Approximately 308.300 pairs breed in the region, 80% of which are found in five colony clusters. These colony clusters are associated with deep canyons and basins that intersect the continental shelf. Ad6lie Penguins confine foraging activities [0 regions over these deep features that are within 20..50 kIn from colony clusters. Winter distributions in the Weddell and Bellingshausen Seas exhibit similar spatial heterogeneity and also occur in association with anomalies in bottom 10IX'graphy. Available daylight in winter restricts available foraging time, an analog to summer conditions when similar restrictions occur due to the need to provision chicks. It is hypothesized that summer and winter heterogeneity in the distribution of Ad61ie Penguins is maintained by behavioral mechanisms, but is causally linked to the juxtaposition of suitable bottom topography, nesting habitat, pack ice and available daylight, features associated with high prey availability. Changes in the spatial and temporal juxtaposition of some of these features over ecological and geological time due to climate change are likely 10 drive changes in the populations of Ad61ie Penguins. Different regions of the Antarctic appear to be out of phase with each other from the standpoint of climate change for reasons that are not yet clear. As a result, trends in Adelie Penguin populations are not synchronized, but instead reflect region-specific changes in climate.