In the tropical lowland forests of central Panama, you may encounter a singing competition with stakes higher than American Idol. It’s here that chestnut-backed antbirds sing duets to defend their territories.

Chestnut-backed antbirds are small insectivores that form long-term pair bonds, a lifelong monogamous relationship between male and female birds. The pairs live together year-round on territories that average about 10 square acres. The birds are common in central Panama, and they’re vocal, which makes them easy to locate.

All of these factors made chestnut-backed antbirds the perfect candidates for Erin Stewart’s master’s research. “In general, I was really interested in this project because there’s a lot of gaps in knowledge of the basic life history of tropical species,” explains Stewart, a graduate student in the UW Department of Zoology and Physiology. Almost all bird studies focus on the breeding season, but Stewart wanted to understand how birds behave when it’s not the breeding season. Additionally, Stewart wanted to look at a species where females participate in territory defense, rather than just focusing on male singing.

For chestnut-backed antbirds, a territory challenge is more of a dance-off than a knife fight. The birds rarely get closer than about five meters from each other. Primarily, they counter-sing at each other, but sometimes they also fan their wings, displaying white wing bars on the front of their wings. “Counter-singing” is where the duets come in: males start singing a tune, and then females back them up to prove that they’re not worth messing with.

Stewart wanted to understand these defensive duets. Do mated pairs sing in synchrony, in order to prove they are very in tune with each other? Or do they sing sequentially, to make it very clear any intruders will be facing the wrath of two birds, not just one?

To investigate this question, Stewart recorded the birds’ duets. Then, she set up recordings of duets with more overlap between the male and the female, and recordings with less overlap. She placed these recordings in the middle of the birds’ territories to see how aggressively they responded to each kind of recording.

Stewart found that birds tend to sing sequentially, and they tend to respond more aggressively to sequential songs. Numerical advantages, rather than synchronicity, are more threatening for this species.

Over the course of her six-month-long study, Stewart also discovered other new facts about chestnut-backed antbirds. Previously, two- and three-note songs were the most common and substantiated calls, with four-note songs rarely recorded. Stewart documented one- and four-note songs as well.

Also, although it’s generally thought that females of most species of birds are less aggressive and follow the male’s lead when singing to defend their territory, in this species, it varied from pair to pair. Sometimes, females would start singing before males, or they would even respond alone.

Stewart’s research demonstrates that there’s much more to know about nature’s karaoke routines, particularly in the neotropics.

To learn more, contact faculty advisor Patrick Kelley at patrick.kelley@uwyo.edu.

This article was originally published in the 2024 issue of Reflections, the annual research magazine published by the UW College of Agriculture, Life Sciences and Natural Resources.