UMD Researchers Uncover Evidence Birds Listen to Birdsong Much Differently Than We Do
Research led by psychology Professor Emeritus Robert Dooling (below) uncovered surprising facts about how birds hear birdsong, including zebra finch's seeming indifference to the sequence of sounds, while instead focusing on the texture and tone of the sounds.
How exactly do birds “talk” to one another? And how can birdsong research help us understand communication in humans, too?
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.
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