Imagine an alien species with a much slower perception of time than humans. For the aliens, perceiving human actions would be like watching a time-lapse movie in which motion appears to be sped up. Watching a gymnastics floor routine would be baffling: the alien would be unable to perceive the rapid movements the gymnast is executing. All it would see is a person zipping from one end of the mat to the other. Why, it wonders, are the human judges so excited by someone moving across the room?
This is often the way humans perceive the movements of small animals that have a more rapid perception of time. Animals often experience the world in ways that are beyond human capacities; if we don’t take their perceptual systems into account, we may overlook sources of social information for that species. Solving the mysteries of animal behavior often involves immersing ourselves in their perceptual world. If they’re birds, it means taking a literal bird’s eye view of their behaviors.
Some striking recent examples were only discovered when they were filmed with high-speed cameras, allowing us to view their behaviors in “bird time,” the far finer temporal scale in which they view the world. The manakins are a family of birds best known for elaborate, ricocheting, moonwalking courtship displays, with the exception of the black manakin. Its display—we thought—consists only of rapid, small hops.
Yet when filmed and slowed down, researchers discovered that each hop was in fact a 360-degree backwards somersault, lasting 0.37 seconds, and completely imperceptible to the human eye. Similarly, the cordon bleu finch, a common pet bird, was thought to have a simple hopping courtship display. When slowed down, these finches were revealed to be “tap-dancing,” alternating from foot to foot. In the case of both the manakin and the finch, although their displays initially appear simple and uninteresting to humans, females of the species pay close attention to male displays. They are very picky about which they prefer, as these rapid displays are challenging to execute correctly and provide a wealth of information about the physical quality of the male.
These ideas are still novel to many scientists. To study animals appropriately, we need to study them through the lens of their own umwelt, the way in which a particular organism experiences the world. How animals’ perceptual capacities allow them to see their environment, how evolution has shaped them to utilize different sources of information, and how their social lives are structured all influence the ways in which they learn and think. This idea is critically important for the study of communication.
What would happen if we applied this idea of “bird time” to song learning in the zebra finch, the most common model species for human speech development? Song learning in these birds has been studied for decades, but almost never in a social context. Usually, researchers let birds expose themselves to adult song by pecking a key, and their subsequent learning is assessed. Based on these studies, zebra finches were thought to learn solely via imitation, with no social information required.
We wanted to understand what information might exist in the immediate environment that a young learner could utilize. We began by watching the birds interact. What we saw surprised us. When females heard song, they sometimes responded with a small bodily movement, such as briefly fluffing up their feathers. Were these females’ cues giving young males information about the quality of their song?
In our new paper in Current Biology, we investigated the effect of these tiny gestures made by females. We found that males used the gestures of females in response to their immature singing (similar to a human baby’s babbling) to guide their song towards more attractive forms. To test this idea, we showed young males videos of females performing “fluff-ups” in response to their own production of immature song. Males that received this social feedback while they were learning ultimately produced better song.
Although immature song has always been assumed to be done purely for practice, we found that it has an important function: the babbling of baby birds catalyzes informative social reactions. Our findings mean that we have barely scratched the surface of how zebra finches, our most important model for human speech learning, develop their vocalizations. Only one other species of songbird, the distantly related brown-headed cowbird, is known to incorporate female social feedback into song learning. It is unknown if other species might use similar active social guidance of song, as no one has looked!
There has been far more research done on male singing behavior than on the female reactions to song. Since females are the arbiters of successful song—they judge whether a male’s song is good enough to select him as a mate—understanding the evolution and development of communication requires study of young learners and female listeners as a linked system of mutual influences.
In our lab, we also study human infants, and are discovering parallel methods of learning in birds and babies. Similar to the case in songbirds, human language is traditionally thought to be so complicated that it cannot be learned without some information about its structure already existing in our heads when we are born. However, eight-month-old humans perceive patterns in their native language which are not obvious to adult speakers, who are too wrapped up in the meanings of words and sentences.
When babies are played simple streams of syllables, they can deduce which syllables go together to rapidly identify words, a task which adults find extremely challenging. For a baby, there are structures underlying language that are tractable and learnable from the information available in the environment. If we do not consider the babies’ umwelt, and the ways in which they see, hear, and perceive patterns in the world differently from adults, we will miss the critical information that makes language learning happen.
As adult human researchers studying infants and birds, we are aliens attempting to decipher a foreign way of perceiving the world. To discover the behaviors we cannot see ourselves, we need to pay attention to the reactions of the intended audience, be they parents responding to baby babbling, or female birds responding to male displays.