Simultaneous effects of age and territory quality on fecundity in Bonelli's Eagle Hieraaetus fasciatus

Several factors that interact with a bird's age are likely to affect breeding performance. Because of habitat heterogeneity, individuals of different subpopulations may experience different probabilities of breeding, depending on the habitat that they occupy. The aim of this work is to test the hypothesis that age and territory quality independently affect breeding performance. We analysed data on breeding biology and fecundity at 298 breeding sites of Bonelli's Eagle Hieraaetus fasciatus in Andalusia from 1980 to 2000. Our data confirmed that age and territory quality simultaneously affect reproductive output. After controlling for the effect of year and age, breeding performance varied among territories. Independently of territory quality, the age of breeding birds affected the number of fledged young and variance in productivity.