Pigeons: Masters of Pomp and Circumstance
by Howard Youth
A Rainbow of Pigeons
When it comes to variety of color and pattern, no other free-living bird compares with the feral pigeon. Common plumage colors include the blue-bars, silver-backed, blue-headed birds that resemble wild rock doves; checkers, dark birds with checkered backs; pieds, birds with big white splotches; spreads, all-dark birds; reds; whites; and red-bars, reddish birds with a similar pattern to the blue-bar. Most or all of these plumages are represented in large city pigeon flocks. Feral pigeons often choose mates based on plumage color or pattern.
Studies show that ferals often choose mates based on their color patterns. This type of breeding, known as assortative mating, varies by location, and has helped perpetuate the various color types commonly seen throughout cities.
Since 1994, University's Laboratory of Ornithology has run a program called Project PigeonWatch, which aims to survey regional differences in the prevalence of different color types of North America's pigeons. Still in the data-collection phase, Project PigeonWatch enlists the help of school groups and other participants who monitor local pigeon flocks and submit tallies to Cornell twice per year. Their coverage provides data from all across the continent that would otherwise be nearly impossible for the ornithologists to collect by themselves.
I joined Project PigeonWatch earlier this year, and, armed with my pigeon identification chart and tally sheet, casually surveyed local flocks. At Cleveland Park, a residential neighborhood in Washington, D.C., I found a flock of 41 feral pigeons feeding outside a Metro rail station. My survey revealed that the flock consisted of 46 percent checkers, 17 percent blue-bars, 17 percent pied, 9 percent spread, and about 2 percent (one individual) each of red and red-bar birds. I could not easily assign a plumage type to roughly 7 percent, or three, of the birds. I found a similar distribution of colors in a larger flock outside the National Museum of Natural History on the Mall downtown. My quick unscientific survey loosely confirms formal pigeon research.
Studies done in North America and Europe have revealed interesting distribution patterns and behavioral differences between the color types. For instance, checker- and spread-colored birds are found most frequently in large cities in North America and northern Europe, while blue-bar birds are common in rural areas and in southern cities of Europe.
Findings about behavior differences between these common color types have been striking. For instance, researchers learned that blue-bars tend to gather in smaller groups and travel more widely in search of food. They also defend their nests more vigorously from other pigeons.
Checkers and spreads have been found to breed more in winter than blue-bars do, and they tend to be concentrated in cities. In temperate-climate winters, most birds' gonads are small and inactive, enabling birds to store their energy as fat so they can survive severe weather. However, in checkers and spreads, the gonads usually stay enlarged year-round. It's likely these birds can ride out winters with less fat due to the urban abundance of shelter and food.
Other findings include a north-to-south increase in red-plumaged city pigeons in North America and Eurasia, and offer reasons why predominantly white pigeons are usually so uncommon. White pigeons tend to be the least territorial of the color types; the majority of their offspring, due to interbreeding and back crosses, lose much or all of their white color; white coloration may not provide as much thermal heating as darker plumages; and light birds stand out to predators such as hawks and cats. Despite this, in a very few areas, such as Honolulu and Seville, Spain, up to 80 percent of local flocks may consist of white birds.
Billing and Cooing
In our quest to answer life's riddles, we have used pigeons in countless experiments, the most famous of which include studies of genetics, orientation, and psychology. But many of us choose to ignore the most obvious research project to which pigeons lend themselves--first-hand lessons in animal behavior. Pigeons, be they city dwellers or rural foragers, are wild creatures exhibiting wild behavior. They are one of the most easily studied birds, feeding, nesting, and courting right under our noses.
Spend a few minutes watching pigeons, and you'll likely witness the behavior leading to copulation. Sexually active birds, usually males, frequently clap their wings together in a sort of advertising flight, and may combine the claps with an ostentatious glide, with wings held in a "V" and tails spread. On the ground, a male "drives," or chases, his mate away from other prospective suitors. A male then struts around his mate, eventually standing up, spreading his tail, and bowing to coo at her. Other intimate pigeon behavior includes billing, often a prelude to mating, when the female sticks her bill down the male's throat and takes an offering of regurgitated food, and allo-preening, when pairs lightly preen each other's heads. Once paired, pigeons may mate for life.
Pigeons often nest high on protected ledges, under bridges, or in abandoned buildings. When a nest site is selected, the male pigeon gathers twigs one by one, placing them next to the female, which sits on the nest and works them into a flimsy platform of twigs and grass or straw. Pigeons usually lay two white eggs that take about 18 days to hatch. Parents share incubation duties, with the male usually taking the morning to afternoon shift. The nest remains covered by one of the parents about 99 percent of the time. This protection from heat loss is especially important in cooler months.
Once the young hatch, they are fed "pigeon's milk," or crop milk. Parents share the responsibility of feeding their chicks this thick fat- and protein-rich substance produced in the parents' crop, a pouchlike compartment in the esophagus. By the end of the first week, crop milk production dips and the parents feed their young increasing amounts of seeds, until by the second week, the crop milk is gone. Four to six weeks after hatching (it varies by season--about four weeks in summer, six in winter), young pigeons leave the nest. Pigeons can average about six broods of two young per year, but due to the vagaries of harsh weather, disease, and predation, only four to six nestlings (between one-third and one-half) survive per year. Compared with many songbirds, in which about 30 percent of young survive, this is a good survival rate.
Although pigeons are among the most thoroughly studied animals, great rifts remain in our knowledge of their biology, even in the Washington area. "Considering this bird's close association with people, it is remarkable that almost nothing is known about its breeding biology in Maryland," writes Eirik A. T. Blom in the Atlas of the Breeding Birds of Maryland and the District of Columbia. "As far as ornithologists and birdwatchers are concerned, the [feral] rock dove barely exists, despite its large numbers." Cornell's Margaret Barker thinks we ought to look a little closer. She conducts workshops with city school groups that have signed up for Project PigeonWatch, and has faced pigeon hecklers dozens of times. "Many students consider pigeons rats with wings, cowards, or like to kick them, or think they're freeloaders," Barker says. "But that's before we go out and look at individual birds and their colors. My personal experience in doing workshops is that when people look a little more closely, they want to treat pigeons with respect."
(ZooGoer 276) 1998. Copyright 1998 Friends of the National Zoo. All rights reserved.)
