Big Lift for a Little Falcon
Volunteers are erecting nest boxes in some unlikely places to keep kestrels soaring in American skies
- Cheryl Lyn Dybas
- Aug 01, 1991
As jets roar all around him, researcher Roger Jones trudges through a field of broomsedge along a runway at Virginia's Dulles International Airport. Undeterred by the racket, he makes his way toward a wooden birdhouse mounted atop a pole, one of the 20 or so nest boxes that dot the sprawling airfield. His purpose: to check for resident American kestrels and band any new arrivals.
But not even a man with a mission can ignore the high-decibel thunder of the British Airways' Concorde. "Cover your ears!" Jones shouts to his three assistants as the supersonic behemoth booms low over their heads.
Meanwhile, not far away, a male kestrel hovers above a field on the edge of the plane's shadow, seemingly unaware of the fuss. "He's probably looking for mice or insects to feed the young in one of these boxes," Jones explains after the Concorde has landed. "There's not much that bothers a kestrel when it's seriously hunting."
The diminutive raptors are a familiar sight around Dulles these days, thanks largely to Jones, an amateur bird enthusiast who started putting up nest boxes at the airport 17 years ago. "Before Roger's project began, we didn't see many kestrels at all in the fields out here," says John Litzenberger, operations manager at the airport. "He provided the birds with something they really needed—a replacement for the trees that were cut down to make way for runways when Dulles was built in the 1960s."
Jones, who has a permit from the U.S. Fish and Wildlife Service to band birds, has taken a keen interest in the plight of the American kestrel. The species builds homes only in naturally occurring tree cavities or those hollowed out by other animals. In "Kestrel Karetakers," a newsletter he publishes from his Northern Virginia home, Jones exhorts readers to erect alternative housing for kestrels, which are finding fewer places to live as trees disappear from their habitat.
But Roger Jones isn't alone in his concern for kestrel homelessness. Around the country, hundreds of altruistic avian aficionados are putting up shelters near open areas where the birds like to hunt. This surge of goodwill toward the little falcons is one big reason why, even with the shortage of natural housing, the kestrels' future is looking bright. While populations of many other raptors around the country decline, "thanks to nest box programs, kestrel numbers are more than doubling in many areas of the country," says Tom Cade, founding chairman of the Peregrine Fund, Inc., in Idaho. As he points out, people are inadvertently giving kestrels a hand in another, surprising way: by building roads. "Highways keep the birds' favorite prey, insects and rodents, on the move and easily caught," says Cade.
That doesn't mean life is easier for the kestrel everywhere people appear on the scene. Changing agricultural practices and continued use of pesticides, for instance, can make even prime farmland inhospitable, if not lethal, to the raptor.
About the size of a blue jay, the kestrel is the smallest and most frequently sighted falcon in the United States, its range spanning most of North America. Early ornithologists dubbed the species "grasshopper hawk," no doubt because of its fondness for large insects. As it searches for food, the kestrel seems to dangle motionlessly above the ground—a feeding style called "hover hunting," unique among falcons.
Another characteristic that sets the kestrel apart from its kin is the male's slateblue-and-rust plumage, which contrasts vividly with the duller, reddish-brown hue of the female. "The American kestrel is the only falcon species in which the male and female show such a marked plumage difference," says Cade. He suggests the birds' coloration helps the similarly sized male and female recognize each other in the wild. Other raptors may determine sex among their own species by the difference in size between the larger females and smaller males or by behavioral differences.
Although kestrels are migratory in northern climes, the birds remain year-round in areas farther south. Throughout their range, males and females seldom mix during winter. As the temperature rises, males begin to establish nesting territories. Come early spring, females move in and wait to be enticed into a nest cavity by a food-carrying male. Some, but not all, kestrel pairs remain together and return to the same nest site every year.
Kestrel females lay their usual five cream-and-brown speckled eggs around April in the mid-latitudes of the United States, earlier in more southerly locales and later in northern areas. After four weeks, the young hatch and remain in the nest for another month. In many parts of the birds' range, newly fledged kestrels make their appearance over grasslands in late summer.
Since kestrels don't excavate their own cavities, they seek out prefabricated homes, such as abandoned woodpecker or flicker holes, or nest boxes provided by people. To secure a hollow, the falcons often must compete with other cavity-nesters like screech owls, starlings and snakes—and they don't always win, as Mark Hoffmann has discovered. One afternoon in Florida, the Maryland Department of Natural Resources biologist peered into a tree cavity that seemed a likely nook for a kestrel. Instead, he found a pygmy rattlesnake. "Most birds of prey won't tangle with a rattlesnake," he says.
Recently, at another site in north-central Florida, Hoffmann studied a population of kestrels and found it declining for reasons that had nothing to do with competition from other species. The birds' numbers dropped from 45 pairs in 1938 to 8 in 1982—a reduction of about 80 percent, says Hoffmann, who blames the decline on the clearing of longleaf pine trees to create farmland. In the past, he says, most farmers left the trees standing because they did not have the equipment to move them. The increased use of tractors after World War II meant fewer trees and, in turn, fewer kestrel nesting sites.
Farming practices may be harming kestrels in other ways as well, especially if the birds' hunting grounds are sprayed with pesticides. At Canada's McGill University, in a huge facility that houses 350 kestrels, biologist David Bird studies the effects of pesticides on the species.
Because of their diet, kestrels were not severely affected by the now-banned pesticide DDT, which decimated populations of other raptors, says the scientist. The chemical accumulated in the tissues of fish and ducks and was passed on to the ospreys, bald eagles and peregrine falcons that ate them. Kestrels, on the other hand, feed mostly on insects, which do not concentrate DDT at such harmful levels.
Even so, preliminary research at the McGill colony suggests that other, commonly used pesticides may kill kestrels. Raptor biologists have recently begun to suspect that the new organophosphate pesticides can, at certain levels, harm the bird's nervous system. "The kestrel is turning out to be an important species for monitoring pesticide accumulation in the food chain," says David Bird. "It is much more likely than other birds of prey to live in agricultural areas, and that's where pesticide use is heaviest."
Fortunately, in most cases the appearance of people in kestrel habitat has been more help than hindrance to the birds. Nowhere is this more evident than, of all places, on the road. With increasing frequency, drivers on many interstate highways in Idaho, Iowa and other midwestern states are spotting kestrels perched atop big green exit signs, scanning the ground for food.
What motorists don't see unless they happen to glance in their rearview mirrors are the nest boxes fastened to the backs of the signs. Every spring, biologists and volunteers in a number of Midwest states brave freeway traffic to hang kestrel houses over the road.
The nation's first highway nest-box program began in Iowa, inspired by one scientist's early-morning jog. Ron Andrews, a biologist with Iowa's Department of Natural Resources, was running along Interstate 35 near Clear Lake eight years ago when he "looked around and saw what appeared to be primo kestrel territory." He noticed a number of the birds hovering or perching near the grassy rights-of-way. "They apparently were hunting for mice or insects, oblivious to the roaring trucks and speeding cars," recalls Andrews. "So I thought, 'If the falcons will hunt along this busy road, why wouldn't they nest here as well?'"
In 1983, with the help of some local Boy Scouts, Andrews attached 20 kestrel boxes to signs along the roadway. Since then, he and others have erected ten times that many kestrel condos, and their efforts seem to be paying off. Later this year, Iowa Governor Terry Branstad is expected to inaugurate the nation's first interstate "kestrel trail," a 200-mile stretch of 1-35 across the state from Minnesota to Missouri, with an average of one nest box per mile. By the end of this nesting season, the project is expected to produce more than 400 kestrel hatchlings—nearly double the number that hatched each year in all of Iowa before the first box was installed.
As word of Iowa's success spreads, biologists elsewhere have launched or begun considering similar programs. In Boise, Idaho, biologists with the U.S. Bureau of Land Management wanted to boost the local kestrel population. So in 1986 they recruited some Boy Scouts and started attaching nest boxes to signs along 1-84 between Mountain Home and Caldwell.
"The boxes were almost an instant success," recalls Karen Steenhof, biologist in charge of the project. "That first spring, kestrels nested in 4 of them and successfully raised 17 young. Now there are 69 boxes out there providing homes for the young of 16 mated pairs."
While most people erect nest boxes to replace trees, field biologist Mark Causey in Prince William County, Virginia, got involved because of another critical shortage—of dilapidated barns. "Kestrels in my area had been nesting in old barns on the county's dairy and beef farms," explains Causey. But as the urban sprawl of Washington, D.C., creeps deeper into the county, he says, many farms have been sold and the barns bulldozed.
For more than a decade, Causey has enlisted local farmers to help him put up and monitor kestrel boxes. He started with five in 1980; now he makes regular house calls to check on and band the occupants of 75 nest shelters.
One May morning, Causey turns off Virginia Route 29 and pulls his pickup truck into the gravel driveway of "The Home-place Farm," home of farmer Everett Kline. It's also home to a pair of kestrels, which have produced young every spring since Causey installed a nest box on the farm five years ago. In the old days, kestrels used to nest between the barn door and hay stacked next to it, says Kline. Now that he no longer keeps hay and the barn has collapsed, he says, "I'm glad the kestrels have the nest box."
As Causey walks away from checking the kestrels' nest, a shrill klee-klee-klee pierces the air. The call, which gives the falcon another of its nicknames, "killy hawk," is a warning that, while kestrels don't mind living next door to man, there is such a thing as too much friendliness.
Despite the birds' occasional irascibility, people go out of their way to lure kestrels to their yards. Take Greg Scott, for instance, a naturalist and photographer in Gilman, Wisconsin. He builds kestrel homes by hollowing out dead trees with a chain saw. One tree, he remembers, "had kestrels nesting in the cavity I made, starlings nesting in an old woodpecker cavity above them and woodpeckers in a new cavity at the bottom of the tree."
Fortunately for kestrels and people who like having them around, the birds aren't too choosy about the company they keep.
Virginia writer Cheryl Lyn Dybas dodged low-flying jets and territorial kestrels while researching this article.