Rules to Sing By
Unraveling the mysteries of bird duets in Puerto Rico's mountainous rainforests.
David comes over to explain that very little is known about how parrots live in the wild. Given that they are so brightly colored and blatant with their voices, this surprises me. But he says that, like the elfin-woods warbler, they are difficult to see. They live in very dense foliage and are almost always observed with backlighting. Most of what we know about parrots we have learned from captive birds, and in spite of how much we know about their mimicry, we know very little about the vocalizing of parrots living in the wild.
Most parrots live what is called a fission-fusion lifestyle. Every morning, the flock leaves a common roost where the birds have spent the night, and they fly off to forage, separating into smaller groups until late in the day, when they gather closer together. As they try to decide on a new roost for the night, the groups of parrots call back and forth, imitating each other’s calls. It has been proposed that this mimicking is to mediate the reuniting of the two groups separated during the day before they settle on a roosting place in the evening.
“That isn’t duetting,” David explains about the exchanges between groups of birds. “That’s song matching.”
In a top corner of one of the big flight cages hangs a metal cylinder with an opening at the bottom and an enclosed compartment at the top. This simulates the parrots' nesting situation. The birds move into tree holes, preferably vertical cavities because they are less accessible to predators. While housing considerations for their breeding are relatively straightforward, the rest––aggression and song exchange between prospective mates––is not.
Once a pair is made, the parrots are monogamous until one of them disappears for some reason or there is what David calls a “divorce,” when for some reason the couple can’t keep it together to raise another clutch of chicks. The male parrots don’t incubate the eggs, but they do feed the chicks.
“What I want to see,” Brian says about the vocal communication research project he has proposed to David, “is if the duets affect how often the males feed the chicks.” In a row of three contiguous cages, Brian will house a female parrot in the middle cage with a male in the cage on either side of her. He will monitor the amount and format of vocalizing, and then see which male she prefers. Once the female parrot has selected a mate, he will house the two together in a larger crate with a nesting cylinder and wait for the chicks to hatch and the male get to work on the provisioning.
“When the pair starts duetting,” I raise my voice against the ratcheting background of clamoring parrots, “how can you tell the two parts from each other?”
"The females make a slightly different sound, more like crying than squawking,” Brian characterizes it. I wonder how he will ever to able to hear it well enough to distinguish this in this pandemonium?
We drive out of the compound with parrot calls still reverberating in our ears. None of it sounded like singing, and I wonder how a bird can be said to duet without making some attempt at melody or harmony or counterpoint. Or at least some audible indication of compatibility. When we stop for lunch I say, “I wonder what those voices will sound like when they get into a duet.”
David gives me a long glance. “That was a lot of what you were hearing this morning.”
Evidently during all the clamor, he hadn’t thought it necessary to point out the exchanges of raucous sequences between the males and females.
“That was a duet?” All those raucous squawks and brays? But what about all those comparisons to happy monogamy?
“That’s what you were listening to.” Apparently, those unlovely sounds haven’t changed his ideas about pair bonds and biological parallels to the bonds between human couples.
Reprinted with permission from Calls Beyond Our Hearing: Unlocking the Secrets of Animal Voices, by Holly Menino, published by St. Martin's Press © 2012. All rights reserved.