This is the kind of conundrum that White has been studying in his large, netted aviary, just north of the Morris Arboretum. There’s another aviary nearby, and he’s building a third, but the main action is inside this 60 x 20 x 12 foot cage. Strewn throughout it, like something out of a B-movie set, are dead trees and branches for the birds to flit about. At one end is a small wooden coop, ripe with rotting seed and droppings; in the middle are a couple of lawn chairs, where White and I sit and watch the 12 juvenile males and 11 females go through their complicated fandangos. (He identifies them by the colors of the bands he’s put around their legs.) They pretty much ignore our presence, which is one reason it’s such an oddly entertaining scene: equal parts high-school dance, co-ed summer camp, and seedy singles pickup bar.
Cowbirds aren’t the only feathered critters here. There are also a few juncos, courtesy of Dr. Deborah Duffy, his post-doctoral fellow. Though White dismisses them as “the little flittery ones with no character whatsoever,” the juncos could play an important part in his studies. If they build their nests and lay eggs in them, then cowbirds will lay their eggs there, too.
Getting the juncos to raise the baby cowbirds wouldn’t just mean less work for White, who during Prime Time (the breeding season) gets up at brutal hours of the morning to hand-feed the little beggars. It would also be replicating nature. Cowbirds bring the whole “It takes a village” thing to a new level, laying their eggs in Other Birds’ Nests (OBNs) and then flying off without a thought to child support. This may not be good for the songbirds that end up raising baby cowbirds. (Only a small number of the roughly 220 species that find cowbird eggs in their nests will recognize the scam and pitch the squatter eggs out.) But it does give the older cowbirds a lot more latitude to explore their options.
“Cowbirds are removed from all the parental-care duties,” says White. “And that, trust me, is a huge constraint on behavior.”
White uses the phrase “developmental ecology” to describe the complex interplay of the birds’ early surroundings and their DNA. It turns out that Cowbird Territory is right at the crossroads of Nature and Nurturemaking it a very rich and fertile field of study.
“Really, it’s a species with no hard and fast rules,” he says. “Through different developmental trajectories I’ve produced birds that can be promiscuous, monogamous, polygamousall of those things usually you talk about as the characteristic of the species, but it turns out that whichever one they end up with depended on its experiences during development. A characteristic of juvenile cowbirds is that you put them in a group and they can change their behavior dramatically within a couple of days, just based on the social milieu of the group.”
There’s some irony there, given that cowbirds were once considered a model of genetic pre-programming. After all, males can singand females can recognizea first-rate cowbird song even if they never heard one before. (And the young ones often haven’t, since they’re raised by other species.) But put them in an environment where they have social options and different experiences, and suddenly their slate is wiped almost clean. Traits the birds display during the breeding seasonthe way a male counter-sings or approaches a femaleare shaped by their surroundings. And some of those traits will determine how reproductively successful the birds will be.
White’s work is “very importantas well as interestingbecause it can hone hypotheses that can explain social behavior across a variety of species, including humans,” notes Dr. Robert DeRubeis, professor of psychology and former chairman of the department. “His work is also important from an evolutionary perspective because it provides a window into the social competencies that may account for the fitness of these birds.”
“I think that David is really on to something very exciting,” adds Dr. Marc Schmidt, assistant professor of biology, whose own field of study is the neural basis of vocal production and perception in songbirds. “Some of his most recent work even suggests that social upbringing can have a profound effect on embryonic development.”
In The Beak of the Finch: A Story of Evolution in Our Time, author Jonathan Weiner notes: “Today more and more evolutionists are doing what Darwin thought impossible. They are studying the evolutionary process not through fossils but directly, in real time, in the wild: evolution in the flesh.”
White’s aviaries are not exactly in the wild (though they’re a lot closer than the average laboratory setting) and some of his studies will require generations of cowbirds to yield results. But still, as Weiner writes: “The Darwinian view of evolution shows that the unrolling script is always being written, inscribed as it unrolls. The letters are composed by the hand of the moment, by the circumstances of the day itself.”
“We need a currency of evolution,” says White. “And that’s the gene. It’s a very nice currency because it can be immortal; it can be passed on from generation to generation. But nevertheless, which genes get passed on are definitely influenced by experiences. So to really understand, you have to deal with this interaction between genes and the environment in a better way than we have so far. And hopefully, there’s where I end up.”
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©2005 The Pennsylvania Gazette
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COVER STORY: The Cowbird Variations