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1. Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions. [ABSTRACT FROM AUTHOR]

The breeding biology of the Red Kite Milvus milvus is still little known in the southern part of its range (Mediterranean), despite recent conservation concerns and major declines in most insular populations (Sicily, Sardinia and Balearics). We report here on the breeding biology of the Red Kite in Corsica in 1996–99 and on recent population trends there. In a 42-km2 study area located in the northwest of the island (Balagne region), breeding density was locally high (1.17–1.78 breeding pairs/km2). Breeding dispersion ranged from loosely colonial to dispersed, with average nearest-neighbour distance of 444 ± 316 m (range 50–2000) (all data as means ± sd). Kites established breeding territories in January–February, and 92.4% of territorial pairs laid a clutch ( n = 238). Laying took place between February and May (mean lay date: 27 March ± 16 days, n = 147). Clutch size averaged 2.44 ± 0.71 (1–5 eggs, n = 96), hatching success 66.9% and fledging success 78.6%. Productivity averaged 1.33 ± 0.88 young per breeding attempt ( n = 221) and 1.65 ± 0.65 young per successful breeding attempt ( n = 173). Overall breeding success was 51.4 ± 38.0% ( n = 88). We describe the growth of young (wing, weight, tarsus and bill) and show a marked seasonal decline in clutch size and breeding performance, with pairs laying earlier producing larger clutches and being more successful than later breeding pairs. Unlike most other insular Mediterranean Red Kite populations that have recently declined, the breeding population in the northwest of Corsica, which accounts for c. 25% of the whole island population, increased from 25 to 35 pairs in 1989 to a maximum of 80–90 pairs in 1997. This increase was probably related to the lack of persecution and a local increase in abundance of Rabbits Oryctolagus cuniculus, following their introduction in the late 1970s, which provided an important feeding resource for Kites. Finally, we compare our results with those from other Red Kite populations studied in Europe. We found that there is a latitudinal gradient in laying date and productivity across Western Europe populations, but no evidence of an insular syndrome in the Corsican population. [ABSTRACT FROM AUTHOR]