Spatial dispersion patterns of Antarctic seabirds

Pelagic birds are conspicuous and ubiquitous components of oceanic ecosystems. Because birds catch prey that are themselves upper level consumers, an understanding of the spatial dispersion of birds at sea will be useful for determining what parts of the ocean are biologically important. In order to interpret patterns of bird dispersion, it is essential to first document how birds respond to patchiness in their environment and how their distributions are influenced by the distributions of other species of birds. My two main objectives are (1) to establish what parts of the ocean are most attractive to foraging birds; and (2) to determine the extent to which species co-occur in space.;In this dissertation, I analyze three sets of strip transects collected from oceanographic research vessels. One of these sets describes the distribution of birds around their nesting colony at Bird Island, South Georgia, at a spatial scale of kilometers to tens of kilometers. The two others were conducted at a much larger spatial scale (1000's of kilometers), one in the southwestern Atlantic Ocean, and the other in the East Wind Drift zone of the Antarctic Ocean. I plotted abundances of each species observed on maps, and then analyzed the observed patterns to detect where aggregations of birds occurred, and to determine the extent to which the distributions of species influenced one another. The data were collected over a five year period, 1982-1986.;I found that species of pelagic birds are distributed largely independently of one another at sea. That is, species do not co-occur at sea either more or less frequently than would be expected due to chance. This result held true at both spatial scales, and in all three geographical areas. This finding suggests a lack of structure at the community level among assemblages of birds at sea.;Some fronts, continental slopes and ice edges attracted foraging birds whereas others did not. The largest aggregation of birds occurred where a major thermal front coincided with an abrupt continental slope, off central Argentina. Hydrographic fronts were less important to foraging birds in the Antarctic than farther north in the subantarctic portion of the South Atlantic Ocean.