Osprey monitoring in the Canary Islands

Between 2004 and 2007, we studied density, habitat features and breeding parameters of the osprey (Pandion haliaetus) population in Boa Vista Island (Cape Verde). A total of 79 nest structures were identified, 37 of which were occupied for at least 1 year during the study period. The osprey population ranged between 14 and 18 pairs, and the mean density and distance between neighbouring occupied nests were 2.58 pairs per 100 km2 and 3089 m, respectively. Occupied nests were found to be significantly further from the coastline and roads than unoccupied nests, but the distances from villages were similar. The majority (81.1%) of the 37 occupied nests were easily accessible to humans. Mean clutch size was 2.59, average productivity was 0.76 young/active nest, and breeding success was 58.8% [Correction added on 13 May 2013, after first online publication: the average productivity was changed from 0.72 to 0.76]. Density in Boa Vista was higher than that in other sedentary island populations in the Western Palearctic, whereas the productivity was the lowest of this region. Clutch size did not vary among Western Palearctic populations, but the differences observed in productivity were likely influenced by local factors that in Boa Vista are attributed to nest depredation by the brown-necked raven (Corvus ruficollis) and to direct human persecution.

We studied nesting habitat selection of the endangered non-migratory Osprey Pandion haliaetus population of the Canary Islands and evaluated the effect of human expansion in recent decades. Compared with randomly selected potential nest-sites, Osprey nests were more frequently found on taller, southwest-facing cliffs, char-acterized by lower human pressure and closer to Yel-low-legged Gull Larus michahellis colonies and Barbary Falcon Falco pelegrinoides breeding sites. Furthermore, changes in some breeding habitat features have been detected in recent decades. According to our predictive models, large areas of suitable habitat are available but unoccupied in the Canaries, and human activities are probably limiting the settlement and dispersion of new pairs.

We describe the adoption and alloparental care of fledglings by an Osprey pair during two consecutive breeding seasons (2008-09) in the small and semi-colonial cliff nesting population of Tenerife (Canary Islands). The intruding broods (two fledglings each year) switched nest a few days after fledging (≤ 10 days in 2008 and ≤ 6 in 2009). They used the recipient nest and perches together with the genetic broods, and received alloparental feeding. The short distance between neighbouring nests and advantageous terrain characteristics of the recipient territory seem to be the main reasons that led to these behaviours.