As they ride the wind, vultures seek dead things, not dying things, using a sense of smell far more highly developed than any other bird's. They can detect a dead mouse under leaves from 200 feet up. They are discriminating, preferring corpses between two and four days dead. (The turkey vulture entry in the definitive Birds of North America Online does note, "Takes live prey occasionally in unnatural situations.")
Another misconception, and one that has caused farmers to shoot them, is that turkey vultures spread disease. In fact the opposite is true. Something in the vulture gut allows them to digest and destroy the agents of diseases such as cholera and anthrax. If another carrion-eater—rat or coyote or hyena or dog—disposed of the infected carcass, contamination would be spread.
To those who prefer not to have vultures pooping on their building ledges or roofs or decks, Lynch says, "Their waste is as clean as any waste can be." But there is some threat to human beings from the other end of the vulture digestive system. If adults are threatened when nesting, they throw up on the intruder or play dead. (The latter seems a poor strategic choice, given their companions.)
Vulture nestlings are also armed with vomit—but the downy-white chicks with sheeplike black faces are still vulnerable to raccoons, skunks, fox, and possums. After successfully repelling a threat, the vulture, ever a model of conservation, re-eats the spit-up food.
Under threatening circumstances, an angry bird can aim green vomit at you from as far away as six feet. Normally, though, a turkey vulture's sociability extends to human beings as well as to its fellows. The people who care for injured wild birds report that vultures are gentle, inquisitive, and smarter than hawks and eagles. Here's the bottom line, from Lynch: "Once they get to know you they don't regurgitate on you."
Like morticians, these dealers in death also die. In the wild, vultures live about 10 years. If death doesn't occur because of old age, it comes from starvation, electrocution at power lines, trapping, shooting, ingestion of lead from animals that have been shot, or getting run over by a car. (A turkey vulture, ungainly on land, has a hard time getting airborne quickly, a serious problem if it's working on road kill.)
What would happen without them? The major vulture news of the last decade gives a clue. A mysterious die-off of Asian white-backed vultures has led to a pileup of domestic animal carcasses and an increase in the population of rodents and feral dogs. It turned out that an anti-inflammatory drug—diclofenac—used on sick livestock kills vultures even in low doses. Though the Indian government is phasing out the veterinary use of the drug, the vulture population hasn't rebounded. One social consequence has been that members of the Zoroastrian Parsi community, who have used vultures to dispose of human corpses, now have to cremate their dead. But that doesn't solve the problem of animal carcasses in a vulture-free world. Let's be grateful the turkey vultures are keeping us from being awash in dead raccoons.
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