Spatial and temporal variation in population trends of Kelp Gulls in northern Patagonia, Argentina

Abstract

Many populations of seabird species with opportunistic or generalist feeding habits have expanded worldwide, possibly because they are using additional food resources provided by human activities. The Kelp Gull (Larus dominicanus) is a generalist feeder that often feeds on urban and fish waste and its populations have been expanding in several regions of the southern hemisphere. In Patagonia, Argentina, it is the most abundant species of gull. However, population trends have been reported for only a few colonies and there has been no evaluation of population changes at a regional scale. In this study we provide an update on the distribution and size of Kelp Gull colonies along 1800km of coastline of northern Patagonia, and assess population trends over a period of 15 years (1994-2008) at different spatial scales (colony, coastal sector, region). In northern Patagonia, Kelp Gulls currently breed in 68 colonies, which range in size from a few to 11000 breeding pairs. Ten new sites were colonised in the study period. Most colonies (74%) are increasing and the overall population increased by 37% (from 52784 to 72616 pairs), at an annual growth rate of 2.7%. Two of the four coastal sectors showed significant annual increases (5%), whereas the other two remained stable. Our results confirm the expansion of populations of Kelp Gulls along a long section of the coast of northern Patagonia, although the observed trends varied with the spatial scale considered. © 2011 Royal Australasian Ornithologists Union.