Movimientos post-reproductivos de la Gaviota de Olrog nidificando en Bahía San Blas: primeras evidencias de migración parcial

The Olrog´s Gull (Larus atlanticus) is a threatened marine bird endemic of the south coast of South America. It breeds only in Argentina (95% in south of Buenos Aires province and 5% in Chubut). The objective was to study the spatial migration patterns of breeders from Bahía San Blas (Buenos Aires) by means of geolocators (GLS). Ending October 2014, 32 GLS were deployed on 18 males and 14 females in Islote Arroyo Jabalí Oeste. The 70% of the GLS were recovered at the beginning of October 2015. A total of 8198 fixes were obtained from January to August 2015 (during the non-breeding season). Spatial density analysis (kernel) showed that during all the studied period core areas of the gulls included the colony, Bahía Blanca and marine areas to the south of the colony. However, 23 ringed Olrog´s gulls banded in Bahía San Blas were sighted during the non- breeding season between the 2009-2013 in coastal areas of Quequén, Mar del Plata and Mar Chiquita. These results are relevant for the knowledge of the seabirds’ movement ecology and also highlighted the importance of enforced protection measures during the non- breeding period in breeding areas of the species such as Bahía San Blas and Bahía Blanca.