Finding Beauty in a Boorish Bird
Scientists take a closer look at pigeons and find that these seemingly ordinary birds are extraordinarily colorful
THE "WILD NATURE 4-H'ers" of Madison County, New York, are taking a field trip, and the wildlife, obligingly, is everywhere. As group leader Denise Almonte dumps a bag of popcorn on the sidewalk, hundreds of pigeons launch themselves from the ornate buildings that surround Columbus Circle in Syracuse, New York, and land a few feet from the group of nine- and ten-year-olds. The clatter of pigeon wings sounds like applause. "They like me!" says Briana Foisia, age nine.
If pigeons like people, not everyone likes pigeons back--as their nickname, "sky rats," attests. Maybe it's the way pigeons seem to target your car with their droppings. But if pigeons can be pests, they've also done plenty to help humanity. With their legendary homing skills, pigeons have been pressed into service to carry wartime messages almost as long as wars have been fought. They've ferried blood samples to hospitals and served with the U.S. Coast Guard on search-and-rescue missions. In 1998, workers even used homing pigeons to smuggle diamonds out of a South African mine.
Consider too, that pigeons probably have spent more time under the microscope of scientific scrutiny than any other bird. They were the first subjects tested in psychologist B. F. Skinner's famous boxes. They've been launched into wind chambers to unravel the mysteries of avian flight. Their anatomy, endocrinology, metabolism and genetics have been studied in minute detail. Yet a few mysteries remain, like the one the 4-H'ers hope to help solve: Why do pigeons come in so many colors?
At this point, it's important to explain that the pigeon we're talking about is Columba livia, aka the "rock dove." The name distinguishes this bird from the more than 300 other species of pigeons and doves in the family Colombidae. Thousands of years ago, in their native habitat (Asia, Europe and North Africa), rock doves probably all looked mostly the same: grayish blue with two dark bars on each wing, a pattern that scientists call "blue-bar."
The Columbus Circle flock includes not only blue-bars but also red-bars, "checkers" (for the checkerboard pattern of light and dark wing spots) and "spreads" (so-named because they looked as if dark paint has been spread all over their bodies). Some experts recognize as many as 28 different feather colors and patterns among feral pigeons, ranging from pure white to virtually pitch-black.
How can a band of kids with a bag of popcorn solve the mystery of pigeon diversity? Because they're not working alone--they're one of 700 groups and individuals enrolled in Project PigeonWatch, a research effort organized by the Cornell Lab of Ornithology and funded by the National Science Foundation. The main goal of this project is to help parents "do" hands-on science with their children. "At first some parents said, ‘Counting pigeons? This is ridiculous!'" says Karen Pate of Tampa's Museum of Science and Industry, which offers family PigeonWatching. "But the children really loved it, and eventually the parents became bigger pigeon watchers than the kids."
While families have fun, scientists benefit. Spread over 47 states and 11 countries, PigeonWatch participants collect far more information than a single university researcher ever could. The first step as a PigeonWatcher, says project leader Mindy LaBranche, is simply to count the birds of each color and pattern in a flock. This step should reveal any geographic differences in flock makeup. And by noticing where certain plumages are most common, scientists may learn why certain colors and patterns persist. For example, other studies in Europe have shown that dark-colored pigeons predominate in the north and light pigeons are more common in the south--perhaps because dark plumage helps to gather the sun's heat.
"Okay," says Almonte. "Let's count those colors." The 4-H'ers hunker down on the pavement, whipping out clipboards and pens while the pigeons fight over the spilled popcorn like baseball fans chasing after a home-run ball. "Ten ‘blue-bars'!" announces ten-year-old Kevin Koval, "and eighteen ‘spreads.'" "I see some red birds," adds Bridgett Mead, age nine.
At one level, says pigeon expert Richard Johnston, it's easy to explain why city pigeons come in different colors. "We humans created feral pigeons," explains the University of Kansas professor emeritus. The birds you see loafing on city buildings or farm silos are not direct descendants of wild rock doves; their immediate ancestors were domesticated pigeons bred for a variety of colors, patterns and body shapes. Modern pigeon fanciers recognize hundreds of domesticated breeds, most of them so different from wild rock doves that Charles Darwin once said he found it hard to believe the flamboyant birds shared a single wild ancestor.
People probably began playing with the pigeon genome 5,000 to 10,000 years ago, when Mesopotamian farmers first began rearing pigeons for food. But as long as people have been creating new breeds of pigeons, pigeons have been escaping, forming free-living or feral populations. Cities are good habitat for runaway birds because tall buildings substitute for native clifftop nest sites. There's also plenty of food in the form of fast-food litter or handouts from bird-lovers. The Columbus Circle pigeons are probably descended from domestic birds brought to North America by European settlers nearly 400 years ago.
By now the pigeons have scarfed up the fourth and last bag of popcorn. The 4-H kids settle on the park benches beneath the tall bronze statue of Christopher Columbus (whose last name, appropriately, means "dove") to tally their counts.
If the reason feral pigeons are diverse is because their ancestors were diverse, an important question still remains, says LaBranche: Why does that diversity persist for generations? When other domesticated species escape to the wild, their descendants either revert to a single "wild" type, or become less varied in appearance. "That's what happens with feral dogs," says LaBranche. "They revert to a kind of basic, muttlike appearance."
But feral pigeons may not feel the selective pressures that wild birds do. "Think of the old adage, ‘odd-man-out,'" says Johnston. "Predators usually take the most conspicuous individual, the one that sticks out." In cities, however, pigeon predators such as falcons and hawks are rare. Thus standing out in a crowd may pose no great risk to a colorful pigeon.
One bird in particular does stand out amid the bobbing birds in Columbus Circle. The pigeon is pale gray all over, with no dark marks. It moves stiffly, limping a little, as if it is injured. When club president Marty Rokoff, age ten, forgets Rule Number One of PigeonWatching ("Move slowly") and stands up suddenly, the other members of the pigeon flock whir back up to the rooftops. But the pale pigeon stays behind, crouching in the shelter of a hedge.
Besides "lack of predation," PigeonWatch poses two other hypotheses as to why feral pigeons persist in a rainbow of colors. One concerns the genetic link that can exist between appearance and behavior. The theory goes like this: Perhaps blue-bars are normally more aggressive, and when the flock feeds, they grab the most food. These well-fed blue-bars would be the birds most likely to pass on their color to future generations. In cities, however, food is plentiful. Maybe feral birds don't have to be bullies to fill their bellies, and so birds of all feathers flock peacefully together.
Another idea has to do with sexual selection. During courtship, pigeons choose their mates based on a number of factors, including color. If pigeons preferred partners with the same color or pattern as their own (scientists call this process assortative mating), the variety of colors would be maintained.
Nancy Burley, a researcher at the University of California-Irvine who has investigated feral pigeon mate preferences, says females do seem to prefer certain colors and patterns (at least among the four choices she tested). But since female pigeons factor into their decisions such qualities as a prospective partner's age, experience as a parent and status in the pigeon community, assortative mating probably doesn't explain why pigeon flocks retain their rainbow status.
Still, PigeonWatchers continue to document pigeon mate choices. It's easy to spot courtship behaviors--which include billing and cooing, plus bowing and tail-dragging. So far, PigeonWatchers have found no evidence that all females fall for a single plumage type; nor do females tend to choose males who look like them. Instead, diversity rules: Sixty-five percent of the time, females choose mates unlike themselves.
The 4-H'ers are gathering up their clipboards and backpacks when one of the accompanying parents points frantically to a tall building nearby. There, on a square granite tower, sits a female peregrine falcon. The big bird stretches her wings and launches from the perch, dropping swiftly in a smooth curve that ends ten feet above the bush where the pale pigeon hunkers forlornly. For several heartbeats the falcon hovers like an oversized hummingbird at a nectar feeder. But the shrubbery is dense and prickly. Finally the bird flaps her wings heavily and returns to her original perch.
What this scenario suggests is that if feral pigeons have so far maintained their diverse plumages because there aren't many predators around to snatch the birds that stand out . . . well, that situation may be changing. "We have a natural experiment in progress," says LaBranche. "Just in the last decade, the number of peregrines living in major U.S. cities has just skyrocketed," thanks to a captive breeding and restoration program. And city peregrines like to eat pigeons.
LaBranche sees this as an opportunity to expand PigeonWatch in the future. "I'd like to look at cities with and without peregrines, to see if there are differences in the composition of their pigeon flocks," she says. Many cities with resident raptors also have "falcon-cams," video cameras trained on rooftop nests that broadcast the action to local cable stations and Web sites. "PigeonWatchers could scan the videotapes and record what colors of pigeons are being eaten," LaBranche says.
Okay, maybe you'd have to love pigeons a lot more before you'd volunteer for that job. But give it some thought. And the next time you see some pigeons in the park, check those colors.
Pennsylvania writer Cynthia Berger has new respect for pigeons after reporting this story. To learn more about Project PigeonWatch, go to www.birds.cornell.edu/ppw.