Our environment is filled with sounds from bird songs to sirens, from music to barking dogs. As humans we’ve mostly learned what each sound means and we respond appropriately—we may seek shelter when we hear a siren and run to grab an ice cream when we hear the ice-cream truck.
Animals also respond to auditory signals in their environment. When an American Robin hears the calls of an Eastern Screech-Owl, it’s likely to move closer to the owl and call aggressively to persuade the owl to leave. Other songbirds might hear the call of a Tufted Titmouse and come closer to discover more foraging opportunities. Do birds learn to associate the call of an owl with danger and calls of other species with food, or is their response innate?
New research in The American Naturalist set out to answer this age-old question—is an animal’s response to auditory signals innate or learned? Luis Sandoval, associate professor at the University of Costa Rica, and David Wilson, associate professor at Memorial University of Newfoundland and Labrador, designed a clever experiment using playback of Black-capped Chickadee calls (the harsh chick-a-dee-dee-dee) and songs (the fee-be-o) to determine if a bird’s response is innate or learned. In North America many songbirds come closer, elicit alarm calls, or begin actively foraging when they hear chickadees calling, making the chickadee the perfect species to test their question.
Sandoval and Wilson gathered up examples of Black-capped Chickadee alarm calls and songs from the Macaulay Library and their own collection. They then played the calls and songs to year-round resident birds in Costa Rica, Colombia, and Brazil who are unfamiliar with chickadee vocalizations. To tease out whether residents might be learning to respond to chickadee calls from North American migrants who are familiar with chickadee vocalizations, they used playback during times when North American migrants were and were not present. Sandoval and Wilson hypothesized that if resident birds responded more strongly to the calls but not the songs of the Black-capped Chickadee, regardless of the presence of migrants, that could indicate that the behavior is innate. If the response is learned, Sandoval and Wilson predicted that resident birds would never respond to the unfamiliar chickadee calls or songs because they’ve never experienced the sound before.
Sandoval and Wilson found that 38 different non-migratory species responded to the alarm calls of the chickadee by approaching within 5 meters of the speaker. Resident species responded more to the alarm calls than the songs and their response didn’t change in the presence of migrants. The authors suggest that their results indicate that the response to the chickadee call is innate.
Having the ability to respond to unfamiliar signals, Sandoval says “is advantageous because it allows a species to recognize danger without having been exposed to the signal before.” If a species doesn’t recognize that the call of a chickadee means danger the first time they hear it, they might not live another day to learn the signal. “Being able to take in clues from the environment is basic to survival,” says Sandoval.
“The innate response,” Sandoval says, “is likely driven by the number of calls given over time. It’s more about the information in the call than the pitch or other characteristics of the call.” Frequently repeating the dee dee dee element of a chickadee call is what signals danger.
In a different study, Carolina Méndez, a graduate student at the University of Costa Rica, increased the call rate of a White-eared Ground-Sparrow by stringing multiple chip notes together. Mendez then played the recording consisting of multiple chips and an unmodified recording with a single chip to other birds in the area. Birds responded when they heard multiple chip notes strung together, but birds did not respond when they heard only a single chip note, further demonstrating, Sandoval says, “that the rate of the call and not the characteristics of the call influence the response.”
Pishing, the noise birders often make to bring birds out into the open works in similar ways, says Sandoval, and the behavior could be an innate response.
“One pish doesn’t get you much of a response, but when you do it repeatedly birds approach, because they recognize the sound as an alarm call and approach the sound to locate the danger,” said Sandoval. Pishing itself, Sandoval thinks, is not harmful to birds. “It’s the repeated and continued use that has the potential to negatively affect birds. To me the danger is the overuse of pishing,” says Sandoval. He recommends that birders stop pishing after they get a response from a bird.
“Distress signals, whether they are from pishing or another species calling rapidly, are often ingrained and share some acoustic characteristics that help other animals recognize danger,” says Sandoval.
Sandoval, L., and D. R. Wilson (2022). Neotropical birds respond innately to unfamiliar acoustic signals. The American Naturalist 200:1-16.