A team of scientists from the United States and Denmark has found specialized pecking-related regions in the woodpecker forebrain that show characteristics that until now have only been associated with vocal learning in animals and language in humans; instead of being related to vocalization, activity in these brain regions is related to the characteristic tree drumming that gives woodpeckers their name.
Woodpecker drumming is a highly specialized communication behavior that is performed when individuals rapidly hammer their bill on a tree to generate specific patterns of sounds.
Drumming is used to help negotiate territorial interactions, much like birdsong in some species, and thus it is markedly different than other woodpecker beak behaviors, such as drilling for food and excavating nest cavities in old trees.
Field studies show that increasing drum speeds, or increasing drum length by a few beats, profoundly enhances the display’s threat to competitors.
In fact, birds will attempt to match the tempo of these high-speed drums, even if many individuals fall short of this feat. Additionally, a drum’s rhythm encodes information about species identity, such that changes to its cadence and/or acceleration distort the signal’s recognizability to conspecifics.
Studies in multiple woodpecker species also suggest that drums may encode individual identity and that woodpeckers can distinguish drums produced by their neighbors compared to those that they have never encountered before.
“Both humans and songbirds express a marker gene in these regions called PV (parvalbumin), which has never been found in discrete nuclei within the forebrain of vocal birds that do not learn their vocalizations,” said Brown University’s Dr. Matthew Fuxjager, Dr. Eric Schuppe of Wake Forest University and their colleagues.
“However, when checking for PV gene expression in several types of birds that had not previously been examined, including flamingos, ducks, penguins, and woodpeckers, we surprisingly found that woodpeckers do have specialized regions of the brain that make parvalbumin.”
“These areas are similar in number and location to several of the forebrain nuclei that control song learning and production in songbirds.”
In open field tests with woodpeckers, the authors discovered that the birds’ behavior that triggered brain activity in these regions was actually their rapid drumming, and not their vocalizations.
“Although scientists have not yet established that drumming is a learned behavior, this new evidence from the brain predicts that it is,” they said.
“Finding this system for non-vocal communication that is both neurologically and functionally similar to the song system can help us understand how existing brain systems evolve and become co-opted for new, but similar functions.”
“Woodpeckers have a set of specialized brain areas that control their ability to drum, or rapidly hammer their bill on trees (and gutters!) during fights with other birds,” Dr. Fuxjager added.
“Furthermore, these brain areas look remarkably similar to the parts of the brain in songbirds that help these animals learn to sing.”
The results appear today online in the journal PLoS Biology.
Citations:
E.R. Schuppe et al. 2022. Forebrain nuclei linked to woodpecker territorial drum displays mirror those that enable vocal learning in songbirds. PLoS Biol 20 (9): e3001751; doi: 10.1371/journal.pbio.3001751
This article was first published by Sci-News on 20 September 2022. Lead Image: Vocal learning is thought to have evolved in three orders of birds (songbirds, parrots, and hummingbirds), with each showing similar brain regions that have comparable gene expression specializations relative to the surrounding forebrain motor circuitry; Schuppe et al. searched for signatures of these same gene expression specializations in previously uncharacterized brains of seven assumed vocal non-learning bird lineages across the early branches of the avian family tree. Image credit: Premek Hajek.
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