Habitat use of a threatened gull: the Olrog-s Gull (Larus atlanticus) in Mar Chiquita Lagoon, Argentina

MARÍA TERESA RAVASI; SOFÍA COPELLO; JUAN PABLO SECO PON; JESICA PAZ; MARCO FAVERO

Conferencia; Segunda Conferencia Mundial de Aves Marinas; 2015

Olrog?s Gull Larus atlanticus is endemic to the Atlantic coast of southern South America and is currently listed as Near Threatened. The species breeds in estuaries in Patagonia and, during winter, migrate northwards as far as southern Brazil. During the breeding season the species is considered to have a specialized diet foraging mostly on crabs. However, during the non-breeding season gulls presents a wider spectrum (which includes fish) as result of a possible association with commercial and sport fishing. The main goal of this study was to analyze the habitat use of juvenile Olrog?s Gull in one of the most important wintering areas (Mar Chiquita Lagoon, Argentina). Seventeen GPS devices (CatTraQ live 3) were deployed during the winters of 2013 and 2014. A total of 1088 fixes were gathered by GSM (both seasons combined). A kernel analysis showed that the individuals were chiefly (95% contour area) distributed in a limited area along the mouth of the lagoon of 13 km2. The core area (kernel 50%) covered only 2 km2 and was located in the South of the mouth. The most important area of bird? distributions was characterized by high crab density and as well as concentration of sport fishing activities. No locations were observed in offshore areas and only one individual covered a distance of 43 km to the north of the mouth. In a large proportion of individuals (65%), the core areas were overlapped each other in areas of the Lagoon´s mouth. For the rest of the gulls the core areas were located further north and in subsidiary creeks. These results are of value for the further developing marine conservation measures for wintering areas so far somewhat neglected while addressing the conservation status of the species.