Rules to Sing By
Unraveling the mysteries of bird duets in Puerto Rico's mountainous rainforests.
A few minutes before dawn biologist David Logue pulls the car off a narrow road near the top of a mountain not far from Mayagüez, Puerto Rico, where he is assistant professor at the University of Puerto Rico. The rim of the sun is barely visible on the horizon. Prime time for birdsong.
David and his graduate student Daniel Pereira immediately begin to offload sound gear. We will use it to lure a tiny endangered songbird and tempt it begin singing, to initiate a duet with its mate. The elfin-woods warbler is little studied, but one known fact about it is that it sings duets.
Duetting is the tightly synchronized sharing of song by male and female birds, and for scientists, one of the most baffling of birdsong forms. It is relatively rare. Although more than 400 birds are known to duet, this number accounts for only about 4 percent of bird species. Interestingly, though, the birds that duet are spread across a large number of families.
David has been obsessed by bird duets since his first day in graduate school at Colorado State University. “There was something very appealing about duetting,” David told me. “It was a very mysterious phenomenon that hadn’t been studied very much. Nobody knew why birds coordinated their singing this way, and it was just so elegant and beautiful—I mean, it’s couples singing together.”
His new subjects are very different types of birds with very different voices. Both birds live only in Puerto Rico, both are rare. One is listed as vulnerable, and one is hovering at the brink of extinction. The elfin-woods warbler is a tiny black-and-white bird that has been thought until quite recently to inhabit only the highest altitudes on the island, and the brilliant green Puerto Rican parrot is a larger, heavy bird that leads its loud, scrappy existence in the rainforests nestled low among the mountains. The primary threats to both birds’ survival are the confinement of their populations to an island and their low numbers––once an animal become scarce, the odds against each individual are greater and the toll taken by predation, disease, or environmental change is proportionally much more damaging.
The primary threats to both birds’ survival are the confinement of their populations to an island and their low numbers––once an animal become scarce, the odds against each individual are greater and the toll taken by predation, disease, or environmental change is proportionally much more damaging.
The elfin-woods warbler frequents the mountainside just ahead of us, and our trail scrolls up and down through what the Puerto Ricans call the elfin woods, the scrubby trees and vines that take over near the top of the mountain. As we make our way through this sparse growth, birdsong is picking up, and after a few minutes Daniel stops and looks up suddenly, then points to some foliage high above us. I hear a sharp thin note, and when David listens, he says, “Yeah, give it a try.”
Daniel brings out a shotgun microphone and waits for the song to start up again. Then he turns off the microphone and says, “He took off again.”
“Just one bird right now,” David says, still listening and looking into the leaves, tracking something. “There. See him?”
I do. He is a small dark shadow streaking against the early sun. He lands momentarily behind some high leaves and then speeds off again.