Sociospatial structuration of alternative breeding strategies in a color polymorphic raptor

It has been proposed that niche and behavioral processes may promote the coexistence of alternative color morphs in discrete areas. In this study, we tested the hypothesis that alternative melanin-based phenotypes perform differently when co-occurring in breeding areas. We assessed the influence of microhabitat and social drivers on both the resulting nest-site distribution and the variation in reproductive success of interacting phenotypes of the colonial, color polymorphic Eleonora’s falcon (Falco eleonorae). We combined measures of social, behavioral, and breeding performance, as well as environmental variables under a spatially explicit approach. We found that alternative morphs were segregated over suitable habitats by forming permanent same-color clusters. This pattern was mainly due to social dominance relationships; the pale morph, which was less dominant but more aggressive than the dark morph, settled close to pale conspecifics but far from dark ones. This segregation was also influenced by the settling of dark morph males in less dense areas and at higher altitudes than pale ones. Although the timing of reproduction did not differ between morphs, the dark morph attained higher reproductive output during the study years. The evidence suggests that pale and dark falcons adopt different breeding strategies, with pale morphs behaving highly colonially and dark morphs being more territorial, yet their relative advantages depend on the environmental conditions. We suggest that balancing selection may act on such competitive asymmetries, likely contributing to the evolutionary stability and long-term maintenance of color polymorphism in wild populations.