Extractive foraging behaviour in woodpeckers evolves in species that retain a large ancestral brain

Abstract

Identifying ecological factors that influence brain size evolution is a major challenge in organismal biology. The extractive foraging hypothesis proposes that large brains are more likely to evolve in taxa that extract prey items from hard-to-access substrates, but this idea has received relatively little attention. Here, we provide a comprehensive test of the extractive foraging hypothesis in woodpeckers, a family of relatively large-brained birds that contains many species that feed on wood-boring larvae extracted from trees. Our results show strong support for the extractive foraging hypothesis. First, woodpeckers that use extractive foraging have relatively larger brains compared to species that forage using other tactics. Second, our comparative analyses suggest not only that big brains are the likely ancestral phenotype among all woodpecker taxa, but also that this trait is associated with innovation in foraging behaviour. We suspect that retaining an ancestral large brain likely increases the probability that a given species evolves to become an extractive forager who eats largely wood-boring larvae, given that species that transitioned to a small brain evolved different diets. Thus, the extractive foraging hypothesis likely applies to woodpeckers because of a historical contingency (large brains) that sets the stage for behavioural innovations to better exploit ecological opportunities.