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Territorial occupancy and breeding performance in a migratory raptor do not follow ideal despotic distribution patterns


  • Editor: Andrew Kitchener

José F. Calvo, Departamento de Ecología e Hidrología, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain.


It has commonly been argued that many territorial species select their breeding sites following an ideal despotic distribution model, in which the most productive, high-quality territories are more frequently occupied. Theoretical and empirical studies have shown that this occupancy pattern may have population regulatory consequences, leading to density dependence in heterogeneous habitats. During a 9-year research project in a forested area of south-eastern Spain, we tested some of the predictions of the ideal despotic distribution model and the site-dependent population regulation theory in a migratory raptor species, the booted eagle Hieraaetus pennatus. Contrary to the predictions of the despotic model, our results showed that the temporal pattern of territorial occupation did not differ from randomness, and that the territory occupancy rate was not significantly related to the reproductive parameters considered. At population level, the breeding variables were density independent, suggesting the absence of site-dependent regulation. In addition, we were unable to find significant differences in the habitat characteristics between high-quality and low-quality territories, classified according to the criteria of both occupancy frequency and average productivity. Overall, our results suggest that booted eagles select their territories at random, probably due to the lack of strong environmental heterogeneity, and that occupancy rate is not a good measure of territory quality for the population studied.

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