Effectiveness of protected areas for osprey survival at intercontinental scale

Protected areas are the cornerstones of biodiversity conservation. Evaluating the effectiveness of PAs for protecting peculiar habitats and sensitive species is of paramount importance to ultimately assess their long-term effects on biological communities. We evaluated the importance of the PAs network at intercontinental scale, across Europe and Africa, for the conservation of the endangered Mediterranean osprey Pandion haliaetus populations (< 100 breeding pairs). We used GPS-GSM transmitters to track the movements of 49 individuals belonging to three different populations, estimated their home range size and modelled the spatio-temporal variability in their use of PAs during the non-breeding period. Ospreys made use of a greater number of PAs in Europe than in Africa. Juveniles had home ranges 2.6 times larger than adults. Overlap between home ranges and PAs was 3 times greater for adults (62.7 +/- 24.8%) than for juveniles (20.9 +/- 21.2%), especially in Europe (> 1.62 than in Africa). Time spent outside PAs was twice as long for juveniles than adults. Mean distance from PAs was 16.3 times larger for juveniles compared to adults, especially when in Africa. Fourteen birds (82.35% of ascertained mortality events) died outside PAs. Osprey survival probability increased with proportional time/space spent into the PAs, and this effect was stronger for juveniles. By spending less time in and using less space of PAs, juveniles are potentially more exposed to threats and, hence, to a higher risk of mortality. More stringent binding measures and the establishment of well-enforced PAs, along with coordinated cross-border conservation strategies beyond PAs, are necessary to ensure the future survival of the osprey, as for protecting wintering waterbird populations at an international scale.