Survival differences of embryos and eaglets in a polymorphic raptor probably linked to colour morph.

We analysed the mechanisms that, together with Mendelian inheritance, may be acting in the maintenance and evolution of colourpolymorphism in the Booted Eagle (Hieraaetus pennatus), using observational data from successful breeding events of mixed pairsformed by light morph males and dark morph females, from a long-term study conducted in south-eastern Spain. Our results show thatdark offspring produced in breeding events involving mixed-morph pairs far exceed the value expected in the Hardy–Weinbergequilibrium. Two-eaglet broods mostly resulted in one fledging of each colour morph and in broods in which only one survived, it waspredominantly the dark morph, with a ratio of 0.143:1 light/dark. In the two-egg clutches where only one hatched, the resulting eagletwas mostly dark morph with a ratio of 0.167:1 light/dark. Furthermore, three single-egg clutches produced a dark morph eagletfledging. However, these biases in embryo viability, chick survival and single clutches accounted for only seven (19.44%) of the 36 dark eaglets obtained. Of the remaining twenty-nine, six (16.67%) were expected according to Hardy–Weinberg equilibrium andtwenty-three (63.89%) were produced by disassortative mating, a phenomenon described in previous studies, whereby heterozygouslight males preferentially mate with dark females, likely based on the imprint of the colour morph of their mother. This long-term monitoring of breeding events has allowed us to understand the importance of each of the combined phenomena that contributes to thepositive bias towards the dark morph in relation to the expected proportion according to the Hardy–Weinberg equilibrium.The document Excel file contains data on the monitoring of polymorphisms in breeding pairs and chicks of the Booted eagle (Hieraaetus pennatus) in the southeastern of Spain. The variables are listed in the file's metadata.