Hummingbird’s call provides new insight about vocal learning

Claudio Mello, Ph.D., a professor of behavioral neuroscience

A team led by Claudio Mello, M.D., Ph.D., has made a discovery that may provide insight about the mechanism that enables people to master hearing and speech: A hummingbird with a call well above the known hearing range of any bird species recorded to date. The black Jacobin was found in Brazilian mountains.

As people age, they tend to begin losing hearing in the high-frequency range. Mello, professor of behavioral neuroscience in the OHSU School of Medicine, is investigating this hummingbird in order to better understand the mechanism by which it hears in this high range. That understanding could potentially be applied to people.

The findings were published March 5, 2018, in the journal Current Biology.

The Mello lab uses an avian model to help identify the mechanism of genes associated with vocal learning. This is important because three orders of birds — hummingbirds, parrots, and songbirds — share this trait with humans, which makes it possible to study the anatomical, molecular and behavioral basis of hearing, speech, and language.

These vocalizations are fast and high–pitched, and do not sound at all like a typical bird sound. The sound is more like an insect, such as a cricket, or like a tree frog.

Mello and colleagues at Washington State University made the discovery unexpectedly while studying many species of hummingbirds in the forested mountains of Eastern Brazil.

The team heard prominent high-pitch sounds that sounded perhaps like a cricket or a tree frog. They determined the sounds were coming from these black hummingbirds.

The researchers suspected the vocalizations had to be at an unusually high pitch, but they didn’t have the equipment needed to measure it. They returned with detectors normally used to pick up the high-frequency sounds of bats. The detectors picked up the unusual hummingbird sounds.

More recently, the team made recordings of the sounds using special equipment designed to study bat calls. The recordings showed that the sounds were quite remarkable, having a high degree of complexity and being produced at high frequency, including components in the ultrasonic range that humans cannot hear. Bird hearing generally has to be tested in a lab, either by recording from the brains of anesthetized birds or by watching how birds respond to sounds. Those studies aren’t suitable to studying hummingbirds in the wild.

The discovery suggests that either black Jacobins hear sounds other birds can’t or that the birds produce sounds they can’t even hear. The researchers speculate that the birds might rely on the unusual calls as a private channel of communication. That could be especially useful given that black Jacobins live among a diverse group of bird species, including 40 other species of hummingbirds.

The findings suggest that the hummingbirds must have an unusual vocal organ, the syrinx, to produce these sounds. They would need to vibrate very quickly and likely have a special composition, which may be different from other birds.

A next step would be to study the black Jacobins’ inner ears to see how or whether they differ from those of other birds.

Funding was provided by an Oregon Health & Science University Tartar Trust Fellowship, an Eastlick Distinguished Professorship, and the National Science Foundation.