Sex and the City Bird How urban avian types adapt mating, nesting, and other behaviors to survive By Chuck Baldwin
CITY FOLKS HAVE ALWAYS SEEN THEMSELVES as a breed apart, tough survivors. Turns out that urban birds, too, may be of a heartier strain. In probing this premise, we at Sierra found ourselves asking some unexpected questions: Is citified sluttiness a survival trait? Does busting a hip-hop move help a metrosexual bird thrive where his country cousin might fail?
To our knowledge, no scientist has yet tested our theory that last fall's Internet video sensation Snowball, a captive cockatoo that sings and dances to the Backstreet Boys, is evidence that avian players are adapting to the rituals of big-city dating. But a recent study by the College of William and Mary did indeed show that--to quote Science News--"female zebra finches, normally devoted to their mates, are more likely to flirt with male strangers" when exposed to city levels of background noise.
With a quarter of U.S. bird species declining or rare, according to WatchList 2007, a joint study by Audubon and the American Bird Conservancy, scientists are increasingly paying attention to how some have adjusted to humanity's spread.
"The urban habitat is usually more severe than the habitats these birds historically occupied," biology professor John Wingfield said following the release of a recent University of Washington worldwide study of avian behavior. "Urban habitats aren't easy, so the birds have to have developed coping mechanisms. . . . In the face of global climate change and human disturbances, such as increased urbanization and deforestation, we may be able to identify species that can cope with such changes," he said. Those that cannot "might even go extinct in the face of increased disruption."
Noting humankind's fascination with (and sometimes aversion to) urban birds, Sierra asked artist Jack Unruh to illustrate a brief tribute to these avian survivalists.
Click to see larger image.
ROCK PIGEONS used to nest in bushes, squat trees, and low rock ledges. But after 5,000 years of living with humanity, they've gone condo, settling in on virtually any flat city surface that offers protection--and usually high off the ground. With generations of use and little "housecleaning," their nests harden into claylike structures that are stronger than the flimsy ones found in more bucolic settings.
About 120 years ago, Eugene Schieffelin released some 100 EUROPEAN STARLINGS in New York City's Central Park. Like many successful newcomers to the city, they turned out to be an aggressive, resourceful, and omnivorous breed that moves in large flocks when young. The starling's numbers now exceed 200 million in North America, giving such populous species as red-eyed vireos, dark-eyed juncos, yellow-rumped warblers, and robins a run for their money.
Sources:The Urban Naturalist (Dover Publications, 1998) by Steven D. Garber Complete Birds of North America (National Geographic, 2006), edited by Jonathan Alderfer
Male EUROPEAN BLACKBIRDS living in cities appear not to stress out as easily as their wild counterparts, and those that tend to stay in town--rather than migrate--apparently develop gonads sooner, begin mating earlier in the season, and have longer reproductive cycles, say researchers at Germany's Max Planck Institute for Ornithology.
In European cities, GREAT TITS, similar to North America's chickadees, have changed their tune to overcome the din of urban traffic. The sounds of the city generally meld into a low-frequency hum that ranges in volume. In response, these birds have dropped now ineffective low-frequency notes from their songs altogether. Since most tits learn to sing from their neighbors, their repertoire has evolved to higher-pitched frequencies with fewer but stronger notes than in the songs sung by their country brethren only a few miles away.
Source: "Cities Change the Songs of Birds"; Current Biology; volume 16; pages 2326-2331; December 5, 2006; by Hans Slabbekoorn and Ardie den Boer-Visser
While humans may associate cities with crime, a study of NORTHERN MOCKINGBIRDS in Florida suggests that these "urban winners" are thriving, at least in part, because their nests aren't as vulnerable to natural predators such as snakes. (Mockingbirds in Berkeley, California, meanwhile, have been known to reproduce the entire sequence of a nearby car alarm.)
Source: Selected abstracts on urban bird ecology
from the 2006 North American Ornithological Conference
The PEREGRINE FALCON, the world's fastest bird, usually lays her eggs on a bare cliff ledge near the sea or in the desert. She and her mate then take turns incubating the eggs while the other hunts, sometimes storing food for future use in cliffside caches. In San Francisco, a population of peregrines has eschewed expected behavior and claimed squatters' rights on Bay Area bridges. These urban dwellers hunt on the wing as falcons normally would, catching ever-present pigeons and starlings at the nadir of deep, fast dives. But they keep their caches of food in nooks and crevices of the city's skyline. One couple, adopting the ethic of the Internet age, has taken to cavorting for a "nest cam" set in a wooden box filled with gravel on the 33rd floor of a downtown building. Their exhibitionism has earned them a worldwide audience and blog commentary that might shame Britney Spears.