The brain circuitry that lets birds learn songs is active when woodpeckers hear drumming on trees, suggesting the abilities may have emerged from similar evolutionary processes
To a woodpecker’s brain, drumming against a tree is a lot like birdsong. The findings reveal substantial similarities in the brain circuitry behind hearing and executing these two major acoustic activities in birds, meaning that they may be modifications of a shared evolutionary template.
For some birds, vocalisations come naturally – a hawk doesn’t have to learn how to screech, for example. Songbirds and parrots, on the other hand, must listen to and mimic older birds to produce their tunes, and special circuits in the brain allow them to do this. Erich Jarvis at The Rockefeller University in New York wanted to know if the brains of birds that don’t learn their calls – flamingos, hawks and others – looked different from those that do. Previous research had shown that the activity of a gene called parvalbumin is boosted in special areas in the forebrains of song-learning birds compared with non-learners. Jarvis wanted to confirm this was indeed the case in a wider variety of non-learners.
He and his colleagues analysed the brains of seven such bird species and were surprised to find that one of them had these parvalbumin-rich sections in the brain: the downy woodpecker (Dryobates pubescens).
Woodpeckers don’t just use their beaks to drill for grubs inside tree trunks. They hammer against trees to make specific sound patterns that communicate territorial information with other woodpeckers. Jarvis and Matthew Fuxjager at Brown University in Rhode Island then led a team that aimed to see if the woodpeckers’ curious brain regions were linked to drumming or to the bird’s simple vocalisations.
The researchers played drumming sounds on speakers near the nesting cavities of 15 wild downy woodpeckers, and then examined their forebrains.
In the birds that heard drumming and drummed in response, the researchers found key genetic markers for recent heightened activity in a region of the forebrain involved in learning and singing in song-learning birds. They didn’t find this in individuals that only called out a “whinny” in response, a common reaction among woodpeckers that hear another’s drumming.
“Brain circuits for complex acoustic communication – whether the sounds be made with the vocal organ or the beak – may have a limited way of evolving,” says Jarvis.
The researchers think birdsong and drumming may have both emerged from “evolutionary tinkering” in an ancient series of connections in the bird forebrain for fine-scale movements in display behaviour.
The findings also suggest drumming behaviour may be at least partially learned, says Jarvis.
Nicole Creanza at Vanderbilt University in Tennessee says it would be interesting to see an even broader sampling of brains across the bird tree of life. Other displays could be studied for links to the motor-learning areas, she adds, such as the elaborate courtship dances of birds-of-paradise and manakins.
Journal reference: PLOS Biology, DOI: 10.1371/journal.pbio.3001751
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