Sans titre

Abstract

The Osprey, Pandion haliaëtus, started to breed in continental France (Loiret) in the mid 1980s. In 1999, a national recovery plan for the conservation of this species was initiated. The conservation efforts, and in particular the installations of artificial nests where natural nests or trees holding nests had fallen down, favoured and sped up the colonisation of new sites by breeding pairs thereby creating a small population in central France. In 2007, 22 pairs were breeding, resulting in an average annual growth rate of the population of 15.1% per year since 1985. research program (R. Wahl) with a capture-mark-recapture design, allowed to describe the breeding phenology and to estimate key demographic parameters for this population. Since 1995, nearly 300 fledglings were ringed as well as a few adults. In average, each breeding pair produced 1.8 ± 1.2 fledglings per year. Individuals were highly philopatric, with nearly all breeding adults coming back to breed the following year, and about 40% of the chicks fledged returning to breed in the study area. Age at first breeding was 3.7 ± 1.0 years for females, and 4.6 ± 1.5 years for males. Recapture probability was high and averaged 0.911. Adult survival probabilities were high and were lower for younger breeding females (0.798 ± 0.076, IC95% : 0.611 – 0.908) than for older females and males (0.921 ± 0.024, IC95% : 0.859 – 0.957). Survival probabilities during the first year of life was 0.379 ± 0.057 (IC95% : 0.276 - 0.495). A matrix population model with four age classes was built to model the dynamics of this population for the next 20 years. The population growth rate estimated with environmental stochasticity was 1.105, indicating that the population should continue to increase in the near future at an average rate of 10.5% per year. Although the high survival, breeding success and early age at first breeding could partly explain the increase of the population size, the rate of increase estimated by the population model remained below the observed rate of increase (1.151). The immigration of individuals, particularly from eastern parts of Germany, probably explains this difference.