Population dynamics and conservation of the Osprey in central France.
Dynamique de population et conservation du balbuzard pêcheur Pandion Haliaetus en région Centre
Résumé
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, and up to 18 pairs were breeding in 2003, thereby creating a small population in central France. A 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, 152 fledglings were ringed as well as a few adults. In average, each breeding pair produced 2 fledglings per year, but the number of fledglings varied between sites and increased with the size of the colonies. 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 3.2 0.4 years for females, and 4.4 1.8 years for males. Recapture probability was high and averaged 0.913. Adult survival probabilities were high and were lower for younger breeding females (0.870 0.098, IC95% : 0.551 – 0.973) than for older females and males (0.971 0.036, IC95% : 0.737 – 0.997). Survival probabilities during the first year of life was 0,512 0.156 (IC95% : 0.236 - 0.781). A matrix population model with four age classes was built to model the dynamics of this population. The population growth rate estimated with environmental stochasticity (1.245) indicated that the population should continue to increase in the near future. 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 (1.643). The immigration of individuals, particularly from eastern parts of Germany, may explain this difference.