Researchers Uncover Evidence Birds Listen to Birdsong Much Differently Than We Do
In a sequence of publications,
psychology Professor Emeritus Robert Dooling and his team have demonstrated that
for zebra finches, the subtle—and to human ears, inaudible—nuances in sound
texture or timbre far outweigh the sequence of repeated sounds, which is deeply
embedded in human communication.
While the quality and tone of
birdsong play key roles in communication for other avian species as well, the
team’s research over several years suggests new avenues of investigation in
using zebra finches in particular as animal models for the processing of sounds
and sequences.
“Going back to Aristotle, people have talked about birdsong in terms of sequences, and in the 1800s before there was any kind of sound analysis equipment, musicians were even trying to use musical notation to capture what birdsong was,” Dooling said. “There was always the idea that as humans we were hearing it the way they were hearing it, but now we know they’re communicating something we cannot understand.”
Earlier studies have shown how, just like babies, young birds can learn a series of sounds and then use them to communicate with other birds. Despite this progress, how exactly birds “talk” to other birds to convey important information is still a mystery.
It’s
one that Dooling and his team in the Ball-Dooling Laboratory—including experts
in behavioral ecology, linguistics, psychoacoustics and neuroendocrinology—are
trying to unravel, working on problems ranging from what brain mechanisms
underlie vocal production to the specializations allowing for the perception of
species-specific song and the coding of meaning in sound sequences.
Gregory Ball, dean of the College of
Behavioral and Social Sciences (BSOS), formed the lab with Dooling when he
moved to UMD from Johns Hopkins University. Ball is a psychobiologist who
studies how hormones act in the brain to affect the learning and activation of
behavior; the two had long known each other as researchers, but Ball said he
was “amazed” by the findings Dooling soon began to produce after they combined
forces.
“You can never assume animals are
dealing with the world like you are, even if what you assume is happening seems
very plausible,” he said. “In essence, you have to find a way to ask the
animal, ‘what is your perceptual world like?’ and what Bob did with these
beautifully designed experiments was to find a way to do that.”
Dooling and his team—including Adam Fishbein, a graduate student in the Neuroscience and Cognitive Science Program (NACS), and Nora Prior, a postdoctoral fellow in the Department of Psychology—focused on zebra finches (Taeniopygia guttata), an Australian bird species in which only males can sing.
Young males practice for
months to learn how to produce a song, which they largely copy from their
father. (The researchers are all affiliated with NACS, and the Ball-Dooling Lab
is part of BSOS' Center for Comparative and Evolutionary Biology of
Hearing.)
Zebra finch songs are made up of
only three to eight distinct notes, or syllables, which are short, buzzy sound
bursts with a distinctive structure. These syllables are repeated in a fixed
order to make up a song. To find out whether the sequence of syllables or the
fine details or timbre of individual syllables was more important, the research
team trained zebra finches to detect changes in a syllable’s timbre or in its
position in a sequence of several syllables.
Human speech typically works in such
a way that while you might say words with a different stress or different
accent, the linguistic meaning is the same. However, if you change the order of
syllables in a word, or words in a sentence, the meaning may
completely change.
Dooling found this is not true for
zebra finches; for example, they cannot hear the difference between the words
“turbo” and “boater” but can hear changes in the acoustic structure of the
syllables “bo” and “tur.”
“Fascinatingly, zebra
finches and other birds outperform humans at detecting these very
tiny changes in the acoustic structure of syllables, performing well beyond
human capabilities but at the same time, struggle to hear changes in the order
of syllables in the song—a task that is easy for human listeners,” Dooling
said.
This shows clearly that human
hearing may not be the best tool to perceive the aspects of a birdsong that are
important for birds, he said.
“The fact that the sensitivity of
birds to the minute structure of individual song elements well surpasses that
of humans strongly suggests that birds are communicating information using an
acoustic channel that is beyond human perceptual capabilities, reminiscent of
the ultrasonic echolocation calls of bats that are beyond the range of human
hearing,” Dooling said.
Birdsong can still provide valuable
information to understand human language. The differences between zebra finches
and birds like budgerigars, or “budgies”—which are more sensitive to the
sequence of sounds—can be used as a roadmap to study how the vertebrate brain
encodes and recognizes learned vocalizations.
Studying the perception of song
syllables also provides the opportunity to understand how biologically critical
information is conveyed in the subtle features of voice for both birds
and humans. A hallmark of language learning involves the interplay of the
auditory and motor systems, Ball said.
“Having examples where that goes on
in another species like zebra finches provides a valuable animal model for
thinking about how these auditory-motor interfaces can evolve,” he said.
This article was adapted from
a release by Research Outreach.
