Mediterranean Gulls Larus melanocephalus wintering along the Mediterranean Iberian coast: numbers and activity rhythms in the species' main winter quarters

Knowledge of the winter distribution of the Mediterranean Gull Larus melanocephalus is poor. The limited and geographically patchy data on the species' winter distribution is of concern because current estimates of the wintering population do not agree with those for the global breeding population. We assessed the winter distribution and abundance patterns of this gull in Mediterranean Iberia, a historically important wintering area for which recent data are lacking. Information for the whole study area was obtained from a systematic boat-based survey over the continental shelf in 2003. Then, particular attention was paid to St. Jordi Gulf, a known hotspot for the species, where we studied the temporal patterns in abundance throughout the winter months, and daily activity rhythms, between 2005-2006 and 2008-2009. To set our results in a global context, the available information of the winter range of the species was collated and synthesised. The results indicate that the Iberian Mediterranean coast is the main winter quarters of the species. An average population of ca. 41,000 individuals was present in the area, representing approximately half the 86,3 1 1 individuals (range 50,747-121,875) recorded across the whole of the species' winter range. At the local scale, the St. Jordi Gulf represented the most important area for the species in winter, with an average of around 17,000 individuals and peaks of up to 45,000 in early and late winter. Thus, we argue that this is a globally important area for the species. Daily rhythms involve birds moving between offshore feeding areas during the day (where they largely consume fishing discards) to inland olive crops and bathing and drinking sites (Riudecanyes reservoir) in the afternoon, and finally to coastal roost sites at dusk (Cambrils). Given the global significance of the population wintering in this small area, measures to protect Riudecanyes reservoir and the marine and inland foraging areas should be implemented as a matter of priority. Further research is needed to assess the actual population size of the Mediterranean Gull global population and its conservation status, as well as the threats that the species faces.