Vultures Take Over Suburbia
They vomit all over the place, urinate on themselves to cool off, and feed on the dead. Now they're disgusting and even frightening suburban homeowners. But vultures are amazing creatures that are a key part of the food chain, and they reveal a lot about wildlife's ability to adapt to us.
"Here they come!" The shout goes out from the far side of a tulip poplar, in the backyard of a slate-roofed house in the historic district of Leesburg, Virginia, about 40 miles northwest of Washington, D.C. I look up. About a half-mile away, black specks pepper the horizon. At first it's difficult to identify the birds. They are tiny, coal-colored filaments, like a child's stick-figure drawings of gulls in flight, adrift in a reddening sky. But after a brief few seconds, this becomes evident: The birds are large. They are numerous. And they are flying straight toward us.
In fact, those birds--mostly black vultures, with a smattering of their red-headed kin, turkey vultures--know exactly where they want to be: roosted for the night in one of the trees beside the big fieldstone house at 212 Cornwall Street. They've been here for weeks. At first just a few dozen settled each sunset into a pair of tall pines. Evening by evening, more joined the roost. Their numbers climbed to 100, then 200, then 300. They filled the pines until boughs sheared off with their collective weight. The roost trees were slathered in excrement, white as candles. On sunny mornings the birds warmed their wings on the house's rooftop. On cooler days they skulked on the gravestones of a small cemetery next door, sliming the markers with chalky feces. Now the acrid scent of their waste wafts down the street. And Leesburg has had enough.
Dage Blixt, a biologist with the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS), points a small pistol skyward. He is a soft-spoken man with close-cropped hair and round wire-rimmed glasses, and he leads the five-person roost-dispersal squad hailed to Leesburg by town officials. A trio of black vultures arrows overhead, bold and muscular in flight. Blixt pulls the trigger and a 15mm Screamer Siren pyrotechnic shell corkscrews into the darkening sky, trailing orange sparks, screeching like a car with locked brakes. The shell narrowly misses a dead vulture, trussed by the feet and hoisted 40 feet into a pine. (Such tactics discourage vultures from a roost site.) The black vultures tuck and roll, surprisingly agile for their size. They circle overhead, confused. But there's no peace to be found. The air is filled with screamer shells and Bird Banger rounds, another pyrotechnic that explodes with a loud report up to about 100 yards in the air. Vultures that do find purchase in the roost trees are "shot" with the beam of a red laser that can reach 800 feet. The light is harmless, but it spooks the birds, and that's the point.
This is the first of 10 nights of vulture hazing in the streets of Leesburg, but it is just a tiny skirmish in a protracted struggle to deal with growing populations of these birds across much of eastern America. Of the three species of New World vultures occurring in the Lower 48 (one of which is the critically endangered California condor), black vultures and turkey vultures are doing a fine job of bouncing back from DDT contamination and heavy persecution in the early 20th century, when ranchers and farmers shot them by the tens of thousands. An increase in deer populations--and a corresponding spike in roadkill and carcasses during hunting seasons--plays a part, too.
Most often it's the black vultures that are, quite literally, pissing off their human neighbors, but these birds are more valuable than they're given credit for. "Vultures are one of the better disease control mechanisms out there," says Christopher Brand, research chief for the USGS National Wildlife Health Center, in Madison, Wisconsin. "They check the flow of infectious wildlife diseases such as botulism and possibly anthrax." (These birds evolved with the ability to metabolize natural biotoxins found in decaying flesh.) And given the way vultures use their sense of smell, they can find carcasses that go undetected by other scavengers, such as opossums, crows, and magpies.
What's more, it's hard to fathom what American roadsides would look like without vulture cleanup crews. A bird on the carcass is better than a few thousand maggots and untold bacteria, reasons Greg Butcher, Audubon's director of bird conservation. "We tend to like the other things that clean up carcasses even less."
Trouble is (from the disgusted-human perspective), black vultures are exploiting urbanizing landscapes, thanks to an increase in food sources such as roadkill and, from all indications, a warmer environment provided by growing acres of asphalt and concrete. In fact, the same things that draw new human residents to a burgeoning area are high on a vulture's relocation wish list: Great roads. Warm climate. Lots of open space but still convenient to good shopping.
If scientists can tease apart the causes of their success, it could help us learn to fashion a world where other living creatures can overcome an ever bigger human footprint. "The attitude is they are too ugly and too common for most people to appreciate. But we don't know enough about these birds," says Keith Bildstein, director of conservation science for Pennsylvania's Hawk Mountain Sanctuary. "We need to understand the biology of successful species, because what makes one species successful can help us better understand those that are really struggling to remain a part of our world."
Soaring on rising currents of heated air, carving sooty gyres hundreds of feet overhead, vultures bring a graceful smudge of life to the birdless skies of midday. A bird common from southern Argentina and Chile north through Central America and the Gulf Coast states, black vultures in the United States were once considered a denizen mostly of the Southeast. But they have marched--or rather soared--north up the East Coast for the better part of a century. (Turkey vultures are much more widely distributed, breeding as far north as southern Canada.) As late as the 1930s black vultures weren't known to breed much farther north than central Virginia. They were found breeding in southern Maryland by the late 1940s, in Pennsylvania in 1952, in New Jersey in 1981, and in New York in 1997.
At the same time, various population surveys have recorded a generally impressive climb in numbers. Between 1990 and 2005, Christmas Bird Count data showed an overall tripling in black vulture sightings. During the same time period, Breeding Bird Survey data from the U.S. Fish and Wildlife Service indicated more than a three percent annual increase--a rate that would double the current U.S. population in less than 15 years. Blixt estimates that the bounce is even higher, averaging about 10 percent. Some states, including Pennsylvania and New Jersey, have even seen the populations jump by a rate as much as three times the national average. "We're starting to realize the link between black vulture population increases and range expansions and human population growth," explains Bryan Watts, director of the Center for Conservation Biology at the College of William & Mary, in Williamsburg, Virginia.
Black vultures are among the most resilient members of the vulture family, even though they are slightly smaller than their cousins, the turkey vultures. Black vultures can better tolerate human presence. While most turkey vultures migrate, black vultures are largely residents. The olfactory bulbs of black vultures are much less developed than those of turkey vultures, so they rely more on sight to find a rotting good meal. They tend to fly higher than the turkeys, spot other vultures circling over carrion, then soar in for the steal. And their smaller size is no impediment to their packlike scavenging techniques; black vultures will gather in large groups and drive turkey vultures off a prize find of carrion.
"They are extremely resourceful," says Bildstein. While conducting vulture surveys in Central America, he has watched black vultures drag coconuts onto highways, wait for passing cars to smash the nuts, then eat from the broken shards.
Many bird lovers find this species' quirky habits and odd looks fascinating. "Watch how black vultures fly," says Elaine Leslie, a National Park Service biologist who has studied New World vultures in Florida. "Watch how they socialize. These are some of the coolest birds out there."
Old World cultures viewed vultures far more affectionately than New World suburbanites. Early Egyptians held that vultures would reveal the site of an upcoming battle by appearing there seven days prior to bloodshed. And their scavenging habits were so highly valued, especially in ancient Egypt's intense heat, that one pharaoh decreed the death penalty for killing a vulture--making it, perhaps, the first protected species.
Even their least savory traits are bewitching. Black vultures vomit defensively--"with wonderful quickness and power," marveled James John Audubon. Their distinctive urinary habits are astonishingly clever; the practice of urohydrosis--excreting down their legs--is a useful means of chilling the blood in their lower extremities and redistributing it through the body to stay cool.
These vultures have elongated, hooked bills designed to probe deep inside decaying bodies of whatever misfortunate beings they come across--be it mammal, bird, or fish. Featherless heads are easier to keep clean, a great benefit for a bird that frequently buries its noggin in rotting viscera.
Then again, from time immemorial vultures have had their share of detractors. Early taboos against touching dead bodies put vultures in a singular category of grotesquery, and Old Testament texts considered them "an abomination among the birds." Charles Darwin, of all people, cheerlessly ranted that vultures were "disgusting" and "wallow in putridity." He might have felt at home in Leesburg.
"They are ugly as *!%#," fumes Alan Ogden, as he plants yellow pansies in window boxes four houses down from the harassment in Leesburg, shaking his head and straining to speak above the pyrotechnic shells screaming in the background. "They smell like ammonia and sewage. I walk around the corner and 50 of them are sitting on gravestones, hissing. It's like living in a horror movie. If it were up to me, I'd kill every one of them."
Fortunately, few people subscribe to that view. But it is also true that roosting vultures congregate near homes and businesses, where they fly from trees to rooftops in the early morning to warm themselves in the sun. Once roosts are established, says Martin Lowney, who served as state APHIS director in Virginia until his recent relocation to New York, the birds "strip shingles from roofs, vomit all over the deck and grill, and tear kids' toys apart."
Vultures gather on communications towers, where their feces irritate workers. At lakeside neighborhoods in Florida and boat ramps in Virginia, large numbers tear apart boat cushions and strip windshield wipers from cars. And, unlike turkey vultures, they "take live prey on a regular basis," says Michael Avery, who runs a USDA wildlife research field station outside of Gainesville, Florida. "Their tight social organization might help them subdue and kill larger prey that turkey vultures couldn't." They are known to have killed and eaten striped skunks and opossums, hatchling leatherback sea turtles, and young night-herons, and ranchers complain that black vultures prey on newborn sheep and calves.
Black vultures feeding at cow-calf operations could key in on stillborn animals or scavenge birth sites. "We can't say it never happens," says Audubon's Greg Butcher, "but there are no studies that directly address how likely it is that a black vulture will kill and eat a perfectly healthy calf. But this is a very common complaint. It must happen, at least sporadically."
In populated areas APHIS phones are beginning to ring off the hook. Typically, reports Blixt, homeowners or municipal officials call the regional APHIS office seeking advice for how to deal with their newfound neighbors. "We first give technical assistance over the phone," he says. "Bang the trees, make some noise, work a spotlight. Get a few neighbors together and harass the birds for five or six nights." Most of the time, he says, that works. But if the birds won't move, the phone rings again.
"If we're asked to physically intervene, it's because there's a major problem. We get the tough cases," he says. "And it's not cheap. A project could cost $4,000." But these days more people are willing to pay. (The tab for the Leesburg harassment did come to precisely $4,000, which the town covered.)
On its face, Butcher figures, breaking up a roost can ease the tensions between growing human and wildlife populations. "Dispersing a roost is a bit like rolling the dice," he says. "They might move to a faraway place and we never hear from them again. Or they might move to a place where they cause even greater problems. But if we move them to a place that's not going to cause problems for humans, then no harm, no 'fowl.' "
Butcher does offer an important caveat: "Coexistence means that all parties continue to thrive, even if they must endure a little discomfort." APHIS reports that 1,827 black vultures were dispersed by agency personnel in 1996, with projects in Florida and Tennessee only. In 2005 that number had climbed to 23,660, with dispersal projects in 14 states and as far north as New Jersey. In that same period the number of black vultures actually killed by federal authorities (under permits from the U.S. Fish and Wildlife Service) soared from 238 to 2,005.
"There will be those times when lethal methods are necessary," says Butcher. "But we should be much more willing to try a wide variety of nonlethal methods, and APHIS research is pretty good at coming up with them."
"If we don't solve this problem, people will take matters into their own hands and do something stupid, illegal, or biologically unsound," says Blixt. "Neighbors tell us about people shooting these birds with pellet guns. That does no good. We usually shoot one to four birds a night [as part of the hazing] on a harassment project. It's still protection in the long run."
Others take a more cautionary note. "We don't want to head in the direction we were with raptor control in the early 1900s, when hawks were shot by the thousands," says Watts of William & Mary. "There are times when lethal control may be justified, but as a last option. There was an effort a few years ago for a permit to take 2,000 vultures a year statewide in Virginia. That's extreme. We have to think carefully about how to resolve these issues."
If development trends of the past century continue, more and more humans will have the opportunity to decide for themselves if black vultures are beauties or beasts. The real problem, both sides agree, is that the balance between humans and wildlife has been thrown out of whack.
In the pale light of a commuter's morning, Virginia State Route 7 is a river of red brake lights, wending east from Leesburg toward the District of Columbia. Hundreds upon hundreds of new townhouses, condominiums, single-family homes, shopping centers, and office suites dominate the landscape. Beside the blacktop, Route 7's shoulders are burdened with the offal of such sprawl: The medians are flecked with fast-food bags, mattresses, and the red smudges of road-killed deer whose half-scavenged ribs rise from the weedy grass like storm-shattered masts.
This is the perfect place to contemplate the causes of vultures' success. "The more you break up the habitat," says Lowney, "the happier these birds are." More roads equal more roadkill, more landfills, more McDonald's dumpsters. There's certainly more to be found in Loudoun County, the home of Leesburg. Since 1990 the county population has ballooned from 86,000 residents to 278,000.
As natural land cover is replaced by parking lots, asphalt, and buildings, air and surface temperatures rise. The U.S. Environmental Protection Agency reports that many urban areas have air temperatures up to 10 degrees Fahrenheit warmer than the surrounding region. This so-called "urban heat island effect" is helpful to birds that require rising columns of heated air to locate food. "There is actually a new, manufactured thermal corridor that extends from Washington, D.C., to Philadelphia and on to New York," says Bildstein. "Warmer urban areas create thermals, and there is no question that soaring birds are using them to great effect."
Global warming may well be bringing them north, too. Black vultures soar higher than their turkey kin, and they tend to feed on larger prey. As overall temperatures inch upward, so does the thermal boundary at which carrion freezes, which makes it unusable to avian scavengers.
The National Park Service's Leslie has doubts: "We need to be very careful with linking climate change to the population change. There are so many other factors, including changes in the prey base [from more plentiful roadkill, for one example], that have enabled black vultures to expand northward."
But others are far more convinced. "Climatic change is the most important factor affecting black vulture range changes," says The Peregrine Fund's Lloyd F. Kiff. "This is a species where there is a direct correlation to temperature. The northern range limit is set by a thermal line that allows carcasses to stay unfrozen. And vultures are like people: They are going to take advantage of every opportunity presented to them."
Their spectral silhouettes catch my eye late one morning as I'm driving down a four-lane highway through the rolling Virginia piedmont. I switch on my hazard blinkers, pull off the shoulder, and grab binoculars as the car shudders from the turbulence of passing trucks.
Fifty yards away, two dozen black vultures and a handful of turkey vultures work over a large catfish carcass that they've dragged about 40 feet from the edge of a small pond. For the moment an older, gray-headed bird has control of the fish. He holds it with his left foot and sinks his bill deep into the entrails. As his head disappears inside the carcass, like an ostrich sticking its head in the sand, other black vultures hop in to snip a piece of fish flesh.
I watch for maybe 15 minutes. At one point the turkey vultures, shut out from the feast, take a few hops and wing off for prey they don't have to share. Now the king of the rotting catfish stands on one leg and uses a claw of the other to pick a piece of fetid meat from its nostril.
In the soft-focused background of my binoculars, 100 yards distant over a grassy field, red, white, and blue flags flap cheerfully in a stiff breeze: "Welcome!" they read. "Models Open!"
Roads are coming. Trees are falling. Another chunk of Virginia vanishes. More asphalt. More landfills. More roadkill. More vultures. After all, we laid out the welcome mat.
Watching that greedy vulture clean his nostrils while paring the catfish down to its skeletal essentials, I offer a silent resolution: Should these innocuous, if putrid, transplants ever come toting their trashy belongings onto my street, I'll be resolved to stand upwind and offer a neighborly wave of respect.
State of the Bird
Looks: Bulky body, short tail, broad wings, wingspan of about five feet. Plumage all black except for white flash near wingtips; head is featherless and dark gray.
Behavior: Feeds mainly on carrion, which it finds mostly by sight. Soars for hours, scanning for carcasses and watching the actions of other scavengers. Sociable, usually roosting in groups.
Range and habitat: From southern South America north through Central America and Mexico to southern Arizona and throughout the southeastern United States. Expanding range northward; now common to Ohio and Connecticut. Occupies all kinds of open and semi-open country.
Status: Christmas Bird Counts and Breeding Bird Surveys show steadily increasing populations in some areas in recent decades.
Threats: Growing vulture populations and spreading suburban sprawl are bringing vultures and humans into more contact and conflict.
Outlook: Long-term prospects may depend on educating the public about the important ecological role of scavengers.--Kenn Kaufman