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FIRST BREEDING SUCCESS OF OSPREY (P ANDION HALIAETUS ) IN MAINLAND SPAIN SINCE 1981 USING CROSS-FOSTERING

2006; Raptor Research Foundation; Volume: 40; Issue: 4 Linguagem: Inglês

10.3356/0892-1016(2006)40[303

2162-4569

Roberto Muriel, Miguel Ferrer, Eva Casado, Daniel J. Schmidt,

Aquatic life and conservation

The current status of European populations of Osprey (Pandion haliaetus) is clearly different among regions (Saurola 1997, J. Raptor Res.31:129-137).Although the central and northern areas of Europe support large populations in favorable conditions with increasing or stabilized trends, the situation in the Mediterranean basin is unfavorable, with few, small and isolated populations (Thibault et al. 2001, Le Balbuzard pe ˆcheur en Corse: du martyre au symbole de la protection de la nature, Ed.Alam, Ajaccio, France).In Spain there are only two small breeding populations, each consisting of about 15-20 pairs, both in insular territories: the Canary Islands and Balearic Islands (Martı ´and Moral 2003, Atlas de las aves reproductoras de Espan ˜a, Ministerio de Medio Ambiente, SEO/BirdLife, Madrid, Spain).The species was extirpated from mainland Spain after 1981, when the last pair bred in the province of Alicante (Urios et al. 1991, Atlas de las aves nidificantes de la Comunidad Valenciana, Generalitat Valenciana, Valencia, Spain), after a continuous decline in the number of breeding pairs since the 1960s.The Iberian Peninsula is an important passage area for migratory Ospreys traveling between Europe and wintering grounds in Africa, and a small number of northern European birds winter in southern Spain (Saurola 1997).Despite apparently suitable breeding conditions (Casado 2005, J. Raptor Res.39:168-173), Ospreys have been unable to recolonize the region, perhaps due to natal philopatry and low breeding dispersal (Poole 1989, Ospreys: a natural and unnatural history, Cambridge Univ.Press, Cambridge, U.K.).To accelerate the return of the Osprey to the Iberian Peninsula, a reintroduction program commenced in 2003 in the region of Andalusia (Casado 2005).Between 2003 and 2005, 42 young Ospreys were released, by means of hacking, at two locations: a reservoir in the province of Ca ´diz and a coastal marshland in the province of Huelva.In 2005, after 2 yr of releasing juveniles and observing interactions between adults and released young, we recorded three nest construction attempts by different non-reintroduced Osprey pairs close to the hacking site in Ca ´diz.All attempts were less than 40 km from the release point and one was only 2 km away, in the same reservoir.Only one of these three pairs constructed a complete nest and made a breeding attempt, at a reservoir 30 km from the nearest release point.The nest was built on top of an inactive power pole situated over the water near the shore.After a courtship period, from February to early March, the pair started to incubate on 16 March, but 2 d later a strong wind dislodged the nest.The pair stayed one more day at the power pole, but stopped incubating.Failed breeding attempts may reduce site or mate fidelity in subsequent breeding seasons (Newton 1979, Population ecology of raptors, Buteo Books, Vermillion, SD U.S.A.).Thus, to encourage site fidelity, we erected an artificial nest on another pylon 150 m away from the original nest 2 d after incubation stopped.The pair occupied the new platform the next day, showing pre-laying behavior until 29 March, when they began incubating a single egg.This egg was sterile or addled, because it had not hatched after more than 60 d of incubation, which was .15d more than the maximum documented incubation period for Osprey (mean 5 39 d, range 35-43 d, Poole 1989).Because our objective was to encourage successful breeding behavior by the pair, and because we knew definitively that the natural attempt had failed, we decided to translocate two Osprey chicks from a demographically secure population to be fostered by the pair before this breeding attempt was definitively abandoned.Before proceeding, we had to ensure that the pair would be good foster parents, as they probably had no prior breeding experience.Also, collection and transportation of the young from the donor country would take several days.Consequently, we decided to use temporary cross-fostering by placing a chick of another non-endangered species in the nest.Cross-fostering is a manipulative technique that has been employed in many bird species including several birds of prey (Bird et al.