Abstract
A new colony of Olrog’s Gull (Larus atlanticus) was found on a small island in the Bahía Blanca estuary, near Ingeniero White Harbour. The total number of nests was 1635, distributed in 11 groups or sub-colonies ranging from 25 to 530 nests, inside a large Kelp Gull (Larus dominicanus) colony. This colony of Larus atlanticus is the largest reproductive group reported so far. The Bahía Blanca estuary area constitutes therefore the most important reproductive site of this vulnerable species, perhaps comprising more than 60% of the known reproductive population.
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