Coastal Mediterranean Storm-petrel Hydrobates pelagicus populations: isolated small breeding sites or outlying subcolonies of larger breeding colonies?

There are few known coastal breeding sites for the Mediterranean Storm-Petrel Hydrobates pelagicus melitensis in Spain and France, apart from their core breeding areas in the Balearics and central Mediterranean. In spite of the difficulty of documenting breeding in this species, islands closer to core breeding areas have well-known breeding populations, whilst sites in NE Catalonia and France have not, despite thorough research. Ringing effort has provided a different approach to addressing the issue of determining breeding colonies; ringing results suggest the possibility of an irregular, opportunistic breeding at sites in NE Catalonia and France when habitat conditions are optimal. Of 27 birds trapped and ringed in NE Catalonia from 2003-2005, five were recaptures from the Balearics and Murcia, W Mediterranean Spain (15,62%). In contrast, only an average of 0,22% of total Spanish ringings 1969-2002 (n=10.997) were long-distance recaptures. These differences support the idea of a breeding distribution composed of core breeding areas and isolated small breeding sites such as those in NE Catalonia. Given habitat resource variability, such small peripheral area could act as either irregular breeding sites, as some past evidence and body condition of trapped birds suggest or, alternatively, as part of core areas feeding grounds for either adults or non-breeding birds.