By Caroline Catherman
Very few animals learn speech in a way that comes close to the human method.
The repertoire of grunts, barks, and howls of most animals is innate—genetically predetermined at birth. Humans, in contrast, adopt whatever language exists in their earliest environments.
But songbirds learn to sing in a way similar to how humans learn to speak. Their songs introduce who they are, and what they want, which is typically to mate, feed, or defend their territory. Birds and humans share so many similarities that insights from studying the way they develop the ability to “talk” have allowed researchers to try to determine why some human speech, cognitive, and social disorders occur, given the well-established link between speech, brain function and social interaction.
Stephanie White, a researcher and lab director at the University of California, Los Angeles, has studied birds for over 20 years. She says that birds provide the opportunity to study how human speech works because, in many cases, studies of human brain regions are limited to dissecting dead brains.
“Behavior doesn’t translate to a dish,” she added.
Vocal learning in birds
Songbirds, parrots, hummingbirds, and a few other animals learn to communicate in whatever song pattern or language their parents “speak.” Just as nearly any human could learn English or Swahili or Khoisan, nearly any songbird could theoretically attempt to imitate a White-Crowned Sparrow’s song or a finch’s song or a robin’s song, said David Rosenfield, director of Houston Methodist’s Speech and Language Center. It’s all done through a rare ability called vocal learning.
Birds hear a sound in the environment, remember it, and then produce it from memory. But a bird is only able to do this during a tiny window at the beginning of its life, while certain brain areas are still flexible.
If songbirds are not exposed to their tunes within a brief window as babies, their “critical period,” they will never be able to sing like normal wild birds. And that means they won’t be able to effectively communicate. Even if they are exposed to bird songs later in life, they can produce only crude approximations of normal bird songs, according to ethnologist Peter Marler’s famous 1970 study of White-Crowned Sparrows. The study exposed birds to songs at different periods and compared the resulting tunes that each bird sang.
“The bottom line is that if the bird doesn’t hear what it’s supposed to produce, it won’t learn it,” Rosenfield said.
Vocal learning in humans
Human vocal learning operates in a similar sequence, and, as with birds, scientists’ attempts to understand language-related disorders from stuttering to developmental disorders like autism focus on early experiences.
In humans, this critical window to gain fluency in a language covers the first few years of life, and ends sometime between the age of five and the onset of puberty, as found in Elissa L. Newport’s 1990 review in Cognitive Science.
Then, just as babies make babbling noises that slowly transform into words and then sentences, birds will make garbled sounds that are crude approximations of bird songs, and, with practice, transform those into full bird messages.
Marler’s famous 1970 study theorized that birds, like babies, hold a memory of what their caregiver’s language sounded like, compare it to the sounds that they are making, and adjust their sounds accordingly to match the model during language development.
Historical applications of bird research to humans
After realizing the similarities between how humans and birds learn to speak, scientists started testing bird brains for shared brain areas and genes.
Many studies, such as this 2015 report by Andreas R. Pfenning of the Department of Neurobiology of the Howard Hughes Medical Institute and several co-researchers, confirmed that songbirds’ brains share unique pathways for speaking that are found in few species other than humans. A bird’s brain area called the HVC is crucial for learning and producing song—analogous to some speech-related areas of the human prefrontal cortex. This region of the brain helps control Area X in birds, a cluster of around 2,000 genes that are dedicated to producing learned vocalizations. Area X is similar to the basal ganglia, one of the human brain regions that connect with the human prefrontal cortex and plans and controls articulation.
In 2001, the FOXP2 gene became the first gene identified to affect the development of speech in humans, due to its relationship with many other areas of the brain and hundreds of other genes. Later research found it was crucial to birds as well: when baby birds were injected with a serum that changed the way their FOXP2 genes worked, they couldn’t learn to sing a normal song.
Since then, research on shared genes in birds and humans has advanced.
“Not just for FOXP2, but for many genes, there’s a greater similarity in the gene expression profile of these regions [in humans] and birdbrains than not,” White said.
Today’s translational birdsong research
Today, translational research focuses on experimentally manipulating certain genes and brain areas in songbirds to see what happens. Results of these studies help scientists develop hypotheses about the role that these same genes and brain areas play in human vocal learning.
A study published in Science Advances in Feb. 2021, for example, injected birds with a serum that mostly stopped FOXP1, a gene closely related to FOXP2, from controlling other genes in the HVC.
Baby birds who had heard adults singing before the injection were able to learn to sing normally, to complete the vocal learning process without problems. But birds who hadn’t heard an adult sing before the injection failed to sing the notes that would allow them to communicate with other birds. They sang songs that were similar to birds that hadn’t been exposed to an adult teacher at all.
Before this study, researchers knew that FOXP1 would play a role in vocal learning, said Therese Koch, a co-lead author of the study. They now know more about how and why.
“Previously, it hasn’t been possible to disentangle the role of FOXP1 in … understanding an example so that you can copy it, versus the actual learning process of achieving that copy,” Koch said.
This study has important implications for humans. Mutations in the FOXP1 gene can lead to intellectual disabilities, developmental delays and autism-like behaviors in a disorder known as FOX-P1 related syndrome. The gene is also linked to autism spectrum disorder: studies have found that some people on the autism spectrum may have too much FOXP1 expression.
Now, Koch said that she and her co-researchers at The University of Texas Southwestern Medical Center may look further into why exactly this gene could stop birds from learning from tutors, in order to understand why this gene is related to all these human disorders.
“Is it the social fact … that the bird doesn’t care about other birds after FOXP1 knockdown, that it’s just not paying attention?” Koch asked. “Or is it just that it can’t form those memories correctly, because potentially the neurons where we knocked down FOXP1 are involved in storing the memory of a tutor song to guide later learning? We don’t know any of that yet, but all of those would be interesting future questions to look at.”
The future of songbird research
In California, White hopes to take this research even further in her integrative biology and physiology lab at UCLA. Because scientists have identified genes and neural networks involved in critical-period vocal learning in birds, they could in theory target those areas in drugs that will treat communication issues in humans, she said. She added that her lab researchers have tried to identify brain areas to target drugs in their resident zebra finches, but haven’t found anything so far.
“The going model for drug development are rodents and nonhuman primates,” she said. “[But] there’s a gaping hole in being able to treat problems of speech delay, and kids that are nonverbal.”
At the moment, there are no FDA-approved drugs marketed for stuttering. A drug prescribed for children on the autism spectrum, Risperidone, may solve issues like repetitive behaviors, but not the social-communication aspect of autism. White says songbirds may be the animal model solution, but it will take a “big shift in NIH thinking” to get research to that point.
Other experts suggest caution about applying songbird models to treat human communication disorders. Michael Lombardo, who directs the Laboratory for Autism and Neurodevelopmental Disorders at the Istituto Italiano di Tecnologia in Italy, recently published a study linking gene expression in songbirds and humans to early language outcome subgroups. But he said in an interview that there’s not yet enough evidence to link songbird development to treatment for language in Autism spectrum disorder, for instance.
“Anything in songbirds is a much more simplified and specific process than what human language represents,” he said. “It could be that things developed in research on songbirds have no real value for helping treat language problems in children with autism. But I guess we have to wait and see what research shows.”
Caroline Catherman is a health, environment, and science reporter at Medill. You can follow her on Twitter at @CECatherman.