Comparative habitat use by syntopic Kelp Gulls (Larus dominicanus) and Olrog's Gulls (L. atlanticus) in coastal Patagonia

Abstract

We studied comparative microhabitat use by breeding Kelp Gull (Larus dominicanus) and the threatened Olrog's Gull (Larus atlanticus) at six colonies through the distributional range of Olrog's Gull in coastal Patagonia, Argentina. The ranges of values for most of the 13 microhabitat variables measured (related to vegetation, soil and topography) were broader for the Kelp Gull than Olrog's Gull, with those of that latter within the range of Kelp Gull, indicating potential spatial conflict between the two species. There was particular overlap in nest-site characteristics, but differences were observed between the two species. Multivariate analyses showed that the most important differences in habitat between the two species related to vegetation cover and distance to the high-tide line. Compared with Kelp Gulls, Olrog's Gulls placed their nests in sites with lower proportion of vegetation cover, lower percentages of silt-clay in the substrate, and closer to the high-tide line. For both species the patterns of nest-site selection did not vary among colonies, although the extent of differences between the two species varied with availability of habitat at each colony. Although Olrog's Gulls started laying 12–14 days earlier than the larger Kelp Gulls, the latter occupied breeding colonies earlier and may, therefore, interfere with settlement of Olrog's Gulls. Considering the increase in the numbers, colony area and nesting density of Kelp Gulls currently observed in coastal Patagonia, there is an urgent need to implement monitoring programs for both species and conduct studies to better predict the results of their interactions.

Additional keywords:

• habitat overlap
• nest selection
• spatial conflicts