Does rainfall affect the productivity of the Booted Eagle (Aquila pennata) during the breeding period in Mediterranean environments?

Abstract

The breeding performance of birds of prey is often related to changes in rainfall, which affects the productivity of the environment and the availability of food and may thereby affect chick survival. We investigated the influence of rainfall on the productivity of two populations of Booted Eagle Aquila pennata in two Spanish Mediterranean regions—central Catalonia and Murcia—at 29 and 28 breeding sites, respectively, from 2008 to 2012. During the study period, we found significant interannual differences in all of the weather variables, but these did not translate into interannual differences in the high productivity achieved in either area. We modelled the effects of rainfall on productivity through a linear mixed model procedure. This regression model revealed that precipitation did not cause any response in the productivity of the two populations studied. The results were then compared with data available on a Booted Eagle population in Biscay with a reported nest failure of 65 %—attributed by the authors to heavy and prolonged spring rainfall. Although total precipitation during breeding was slightly higher in Catalonia during our study period than that reported for Biscay, the more than 60 % difference in the number of rainy days in Biscay suggests that persistent rainfall is the main cause of nest failure at the latter location. Therefore, we conclude that our model indicates that rainfall has no significant effect on Booted Eagle productivity in Mediterranean environments.