The helmeted woodpecker, Dryocopus galeatus, sports a vivid red crest on its head and bold black-and-white stripes on its undersides. It looks so much like two other woodpecker species in South America that researchers thought they were closely related. However, according to a new genetic analysis, this shy bird is a very distant cousin to the other two, who just so happen to be much larger, socially dominant species.
Familiar examples of mimicry typically involve warding off predators: butterflies with owl-eye patterns on their wings or palatable snakes that look like venomous ones, for example. These new findings highlight a rare form of visual mimicry known as interspecific social dominance mimicry, or ISDM.
From their coloration to their habitats and food preferences, the helmeted woodpecker (pictured above on the left) shares many similar traits with the larger woodpeckers Dryocopus lineatus (above on the right) and Campephilus robustus (below to the right). But when Mark Robbins from the University of Kansas heard the helmeted woodpecker vocalize in Intervales State Park in Brazil, he was stunned that its call sounded nothing like other Dryocopus birds living in the neotropics. The bird was originally placed within that genus about a century ago because of its appearance. However, the calls are much more similar to birds in the genus Celeus, such as this fiery fellow. Kevin Zimmer from the Los Angeles County Museum of Natural History came to the same conclusion independently, based on two decades of behavioral observations.
“The helmeted woodpecker is basically a typical Celeus in Dryocopus clothing,” American Museum of Natural History’s Brett Benz says in a statement. Its plumage converged in appearance on distantly related woodpeckers, and it actually belongs in Celeus. The trio’s findings will be published in The Auk: Ornithological Advances, and it’s available online now at bioRxiv.
By looking like the larger, more dominant woodpeckers, the helmeted woodpecker is less likely to be attacked by those very same birds they’re mimicking. The costs of aggression and competition between members of the same species makes it not worth it. And as a result, the shyer, more submissive woodpecker gains more access to food.
“It has only recently been appreciated that small species may benefit from deceptively mimicking larger species to protect themselves from aggressive attack,” says Yale’s Richard Prum, who helped form the ISDM hypothesis. “This is similar to how a 12-year-old kid walking home from school will look and act tough to try to prevent himself from being harassed by older, bigger kids.” The poorly understood little bird is found in Brazil, Paraguay, and Argentina and has already vanished from much of its range because of deforestation.
Images: K. Zimmer and R.J. Moller