The hairy–downy game revisited: an empirical test of the interspecific social dominance mimicry hypothesis

• Published in: Animal behaviour Vol. 137; pp. 141 - 148
• Main Authors: Leighton, Gavin M., Lees, Alexander C., Miller, Eliot T.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2018
• Subjects: aggression; bird feeders; citizen science; competition; data collection; foraging; game theory; interspecific; phenotype; phylogeny; Picidae; Picoides pubescens; Picoides villosus; plumage; social dominance; woodpeckers; bird feeders; game theory; citizen science; competition; Picidae; aggression; interspecific
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2018.01.012

Understanding the emergence and persistence of convergent phenotypes is the subject of considerable debate. Species may converge on nearly identical phenotypes for a variety of reasons, including occupying similar environments, exhibiting similar foraging ecologies, and for signalling reasons such as mimicry. Interspecific social dominance mimicry (ISDM) is a hypothesis that states that socially subordinate species evolve a phenotype mimicking a dominant species so as to accrue resources and avoid aggression. A recently proposed test case for this phenomenon asserts that downy woodpeckers, Picoides pubescens, evolved mimetic plumage to avoid attacks from hairy woodpeckers, Picoides villosus. We examined this claim with a large behavioural data set collected by citizen scientists. We employed phylogenetic methods and simulations to test whether downy woodpeckers avoid aggression, and whether downy woodpeckers are more dominant than expected based on body mass. Contrary to the expectations of ISDM, we found that downy woodpeckers were markedly more often the target of hairy woodpecker attacks than expected based on their relative abundances. Our empirical data thus offers no support for the strict ISDM hypothesis as an explanation for downy–hairy woodpecker plumage convergence. However, downy woodpeckers are slightly more dominant than expected based on their body mass, albeit not significantly so. Our data therefore lend weight to previous suggestions that the benefits of mimicry potentially accrue from third-party species mistaking the mimic for the model, rather than the model mistaking the mimic for another model. •Downy and hairy woodpeckers share very similar plumage that is not due to ancestry.•We assessed whether downies use shared plumage to reduce aggression from hairies.•We utilized a citizen science data set to assess interspecific behaviours.•Hairies targeted downies for aggression at high rates.•Downy woodpeckers may have evolved mimetic plumage to fool third-party species.