Songbirds' elaborate cries for food show first signs of vocal learning

July 24, 2009

( -- Only a handful of social animals -- songbirds, some marine mammals, some bats and humans -- learn to actively style their vocal communications. Babies, for instance, start by babbling, their first chance to experiment with sounds. Now, new research in songbirds shows that vocal experimentation may begin with their earliest vocalizations -- food begging calls -- and perhaps for a more devious reason than previously believed. The findings could change the way we think about the evolution of vocal learning.

“It may have started as cheating,” says Fernando Nottebohm, head of the Laboratory of Animal Behavior at The Rockefeller University. “By generating a diversity of calls, young birds may trick their parents into losing track of whom they last fed, in effect creating the impression of several individuals.” In this scenario, the most agile vocal dissembler would get more than its fair share of food at the expense of its siblings.

Nottebohm and Wan-chun Liu, a research assistant professor who made the original observations, are quick to say that the interpretation remains speculative for now, but if true, it would complicate the conventional wisdom that vocal learning evolved as an adjunct to reproductive behavior. In temperate climates, most often only male songbirds sing. The message conveyed by song is simple: I am a male robin, mature, single and ready to breed; females are welcome, males stay away. Depending on the listener, song is a lure or a threat. By imitating the song of established seniors with whom they would have to compete, young breeders presumably gained an advantage in courtship and territorial defense.

The vocal imitation expressed by adults, however, is a complex behavior requiring sophisticated underlying , Nottebohm says. How would birds with only innate, genetically foreordained vocal repertoires have evolved the ability? One part of a plausible explanation is that vocal learning emerged initially as a vehicle for creating variability in juveniles before territory and mate are an issue, according to Nottebohm. Such a development would require a simpler beginning brain circuit, which could later become part of the complex brain architecture required for imitation.

The new research is compatible with the idea that vocal learning first emerged outside the context of reproductive pressures. It suggests that the auditory guidance of vocal development — a key sign of vocal learning — originally appeared in the context of food begging and later evolved into vocal imitation used in territorial defense and courtship.

The food begging calls of songbirds were previously thought to be innate, partly because of their simplicity and because they preceded what was believed to be the first stage of vocal learning — subsong. Subsong is a soft, rambling and variable collection of sounds produced in a noncommunicative context. It has often been described as the avian equivalent of babbling in infants. Mature birdsong, by contrast, combines improvisation — as in subsong — with imitation of the song of other adults.

Liu found that while the food begging calls of young males vary considerably from moment to moment and between individuals, those of young females are very stereotyped and all alike. Deafening altered the food begging calls of male juveniles, but not those of females, suggesting that in males, but not females, the food begging calls are already part of a vocal development that relies on intact hearing. Males producing food begging calls also showed an increased expression of c-fos, a neural activity marker in a section of the forebrain known as the robust nucleus, which later plays a role in the control of learned song. Male sparrows without a robust nucleus still make begging calls, but with less variation, so that they are similar to those of females.

Published last month in PLoS One, these observations strongly suggest that vocal learning in male chipping sparrows starts with their food begging calls, and that in this process improvisation preceded imitation. “The evolution of vocal learning is a deep philosophical problem, and we don’t know the answer yet,” Nottebohm says. “But studies like this help us imagine how it might have come to be.”

More information: PLoS One 4(6): e5929 (June 16, 2009), Variable food begging calls are harbingers of vocal learning, Wan-chun Liu, Kazuhiro Wada and Fernando Nottebohm

Provided by Rockefeller University

Explore further: Study in birds suggests method of learning affects how the brain adds neurons

Related Stories

Why the swamp sparrow is hitting the high notes

January 9, 2009

Birdsongs are used extensively as models for animal signaling and human speech, offering a glimpse of how our own communicating abilities developed. A new study by Adrienne DuBois, a graduate student at the University of ...

Opposites do not attract

November 13, 2006

A study conducted at the University of California, Irvine, found that a female budgerigar prefers to mate with a male that sounds like her. Biologists Marin Moravec, Professor Nancy Burley and Professor Georg Striedter conducted ...

What gets a female's attention -- at least a songbird's

March 18, 2008

Male songbirds produce a subtly different tune when they are courting a female than when they are singing on their own. Now, new research offers a window into the effect this has on females, showing they have an ear for detail. ...

Recommended for you

Tiny protein coiled coils that self-assemble into cages

October 17, 2017

(—A large team of researchers with members from Slovenia, the U.K, Serbia, France and Spain has developed a technique that causes proteins to self-assemble into geometric shapes on demand. In their paper published ...

The importance of asymmetry in bacteria

October 17, 2017

New research published in Nature Microbiology has highlighted a protein that functions as a membrane vacuum cleaner and which could be a potential new target for antibiotics.

Fish respond to predator attack by doubling growth rate

October 17, 2017

Scientists have known for years that when some fish sense predators eating members of their species, they try to depart the scene of the crime and swim toward safer waters. This sensible behavior is exactly what evolution ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.