Exploiting the closest productive area: geographical segregation of foraging grounds in a critically endangered seabird

11 pages, 6 figures, 5 tables
While breeding, seabirds are limited to exploiting resources within a restricted area around their breeding site and should exploit the closest productive marine areas within their distribution range. We investigated this hypothesis in one of the most endangered European seabirds, the Balearic shearwater Puffinus mauretanicus (ca. 3200 breeding pairs), restricted to the Balearic Islands. Our aims were (1) to assess whether isotopic evidence (i.e. stable isotopes of δ13C and δ15N) of foraging habitat partitioning occurs among northern, central and southern populations, (2) to geographically locate population-specific potential foraging grounds along the Iberian continental shelf, and (3) to assess whether oceanographic conditions could explain observed patterns of stable isotopes (SI). SI values showed a latitudinal gradient, with birds from the northern population having lower δ15N and δ13C values than central and southern populations. Potential foraging grounds of northern, central and southern populations were centred in Cape Creus, Ebro Delta and Cape La Nao, respectively, results which were supported by habitat models. Oceanographic conditions in each potential foraging ground were different; the northern population used richer, colder and deeper waters compared to the central and southern populations. Chlorophyll a was the main oceanographic variable that explained variation in SI values. We hypothesised that SI differences among Balearic shearwater populations might be a consequence of differences in baseline isotopic values among potential foraging grounds rather than real differences in diet. Our comprehensive study also provides important information for management strategies to conserve this critically endangered shearwater
This study was funded by Govern de les Illes Balears, DISCBIRD (QLRT-2000-00839) and LIFE projects (European Commission) and the Spanish Ministries of Education and Science (ref. BOS2003-01960 and REN2002-00450) and of the Environment (ref. 024A/2002). M.L. was supported by fellowships from Govern de les Illes Balears and Institut Menorquí d’Estudis, as well as by a postdoctoral contract of the Spanish Ministry of Education and Science (ref. EX-2007-1148) and Marie Curie Individual Fellowship (PIEF-GA-2008-220063). J.N. was supported by a researcher contract from of the Spanish Ministry of Science and Innovation (Juan de la Cierva program). M.G.F. and M.G. by Ramon y Cajal and I3P contracts, respectively, of the Spanish Ministry of Education and Science