Rules to Sing By
Unraveling the mysteries of bird duets in Puerto Rico's mountainous rainforests.
When I don’t answer right away, he turns the question around. “What happens if she doesn’t get it right? He attacks,” David winds up his monologue, “because he isn’t convinced she’s the female who is his mate. If she isn’t, he doesn’t want her anywhere near the eggs or chicks he is responsible for—remember, we’re in the tropics, so he is sharing the work of raising the family.”
It’s a dangerous game. The male calls whee-phew, and while his last note is still sounding, the female’s warbling response has to come at exactly the right split-second, on the right part of the beat, and continue in exactly the right yodel, the right sequence of melodic intervals. Otherwise, she could be beat up, and the male could fly off for another, more accurate female.
“It’s like a password,” David says about the strictness of the code. But why would the two wrens need a password? While birds have sound perception that pretty much aligns with our own, their visual capabilities are far sharper than ours. Don't they recognize each other on sight?
All the birds look pretty much alike, he explains, although the males are larger than the females, and in the Neotropics, they are often seeing each other the way we see them, against backlighting or dark foliage. “Remember how hard it was for you to see the elfin-woods warbler this morning?”
It may be hard for the birds, even with their very acute eyesight, to get a good look at each other until they are perching on the same branch. But it is critical to the survival of an animal to be able to recognize its family members, and David believes the coded duet is a means of positive identification, a continuing reassurance that the female bird is the wren’s mate and not some look-alike intruder.
“Do you think it’s the same for the elfin-woods warbler,” I asked, “that there’s something like a code at work?”
“We don’t know enough about that bird yet.”
This is the way that scientists looking at birdlife have to proceed. Bird by bird.
David's second bird-in-the-bush is such a strong contrast to the elfin-woods warbler that it seems an improbable singer of duets, in fact an improbable singer of any kind. This bird-in-the-bush is much closer to hand for David than the elfin-woods warbler because its only populations are captive. He can find them any time.
To have a look at the Puerto Rican parrot, we drive around the western edge of the island and turn south for about thirty miles into the heart of Karst country, where the shoulders of lumpy limestone mountains hunch up through rainforest. We take a tiny road that follows the channel carved by of the Rio Abajo, driving through dense growth in the low moist valley until we come to a locked gate. The bird’s extremely fragile hold on existence is the reason that the José L. Vivaldi Aviary is closed to outsiders.
Native to Puerto Rico and confined to the island, the parrot is a loud-colored, aggressive bird with a typically raucous parrot voice. In spite of these pugnacious characteristics, the parrot is nearly extinct. It numbers fewer than a hundred, and this figure is up from its low of thirteen birds in 1975. The government is involved in a concerted captive breeding program at two sites, one on the eastern end of the island, El Yunque National Forest, and this one in Rio Abajo State Forest.
A young Puerto Rican man meets us to open the gate. Brian Ramos Güivas, another of David's graduate students, has worked at this compound for more than ten years, and he knows the Puerto Rican parrot as well as anyone in the world.
Brian shows us two parrots in a large stand-alone cage, where he begins his customary presentation about the birds and their progress away from extinction. The two birds are a brilliant green and roughly the size of a crow if you don’t consider the crow’s tail. Brian points out a brief bold band of bright red where the heavy, curved beak meets the head and notes that this stripe is more pronounced on male birds than on females. “Also, the eye—inside this white eye ring—“ he indicates the iris—“is yellower in males, and it gets yellower as the parrots get older.”
“Yes, the parrots are aggressive––” he agrees. “Very aggressive. But these two, " he says about the pair eyeing us and sidling a little toward us, "have been hand-raised, maybe because they were sick or needed some kind of extra care, and they don’t show aggressiveness because they’re not afraid––which is not good for the birds that will be reintroduced to the wild.”
The program at the aviary is an intensive operation to replicate the bird’s natural reproductive pattern. It begins with collecting eggs from nesting pairs, incubating them, raising the chicks without providing evidence of the fact that their caretakers are human beings, moving them to a special evacuation building when hurricanes blow over the island, and then, before release, training them to recognize and avoid their predators. In addition to the inefficient foraging and homemaking skills of newly released birds, two innate factors limit the rebound in the parrots' numbers: the birds' aggression toward prospective mates and their apparent inability to take care of more than two chicks. But Brian reports that the staff releases about thirty birds a year, and that losses of newly released parrots are diminishing every year.
The two ogling us from their perch haven’t made a peep. But we can hear plenty of squawking from a wooded area behind the largest building in the compound, and when we approach the flight cages, cacophony breaks out. If one parrot’s squawk is loud, ten parrots in full voice are ear-shattering.