Male chickadees with better spatial cognition sire more extra-pair young

Across animal taxa, females commonly mate with more than one male, even in monogamous mating systems. These extra-pair (EP) copulations and resulting young may increase the fitness of the female via a variety of mechanisms, including genetic benefits. North American chickadees provide an interesting system to study the role of sexual selection via EP paternity, because they are socially monogamous, nonmigratory birds that rely on spatial cognition to recover food stores and variation in spatial cognition is associated with increased survival, longer lifespan, and is heritable. Given spatial cognitive abilities are heritable and associated with direct survival benefits, these abilities may be under sexual selection if males with better spatial abilities sire more offspring and females prefer to mate with such males. We aimed to address these predictions by quantifying extra-pair paternity and comparing spatial abilities of EP males to those of the social male they cuckold in a wild population of mountain chickadees ( Poecile gambeli ). We found that 1. males with better spatial cognitive abilities have more EP young and produce heavier offspring in their own nests compared to their poorer performing counterparts, and 2. EP males have significantly better spatial cognition than the social males they cuckolded. These results suggest that sexual selection is involved in the evolution of spatial cognitive abilities in food-caching chickadees and are consistent with the good genes hypothesis, which posits that females gain indirect genetic benefits via EP young.