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Why is it a bad idea to scare a vulture?

The Indian government wants its vultures back. Yes, the unattractive, carrion-feeding and generally reviled birds of prey are being bred in captivity in an effort to save the avian species. Why such fretting over the vile vulture? Vultures often feed on dead bodies of sickly animals and curb the proliferation of bacteria. If they disappear, it could open the door to a spike in diseases, including anthrax and brucellosis in livestock, which could then spread to people [source: Gross].

The population of Oriental white-backed vultures in India has dropped from tens of millions to around 11,000 as of May 2008 [source: Morrison]. Around 97 percent of two related species, the long-billed and slender-billed vultures, have also died off in India in large numbers [source: Morrison]. Scientists have identified an anti-inflammatory drug called diclofenac as the culprit. Banned from use in India in 2006, ranchers used to treat their livestock with it. If cattle given diclofenac died, and vultures fed on their carcasses, it took only one exposure to the tainted meat to kill the birds [source: Morrison].

The vultures found in India and the Eastern Hemisphere are collectively known as Old World vultures. The 12 existing species of Old World vultures are related to hawks and eagles and build nests out of sticks. The Western Hemisphere is home to seven species of New World vultures. Unlike their Old World counterparts, New World vultures don't build nests and have been genetically linked more closely to storks. These Western vultures include well-known species such as the California condor, turkey vulture and American black vulture.

Although they hunt down rotting carcasses of dead animals, vultures are referred to as birds of prey. They soar at altitudes thousands of feet above the ground in search of meat. New World vultures in particular have acute senses of smell to help them locate their meals. But even though they feed on nature's garbage, vultures are surprisingly sanitary birds. For instance, they have no feathers on their heads, which allows them to stay cleaner while digging into messy carnage that may contain unhealthy bacteria. Vultures also urinate on themselves to keep comfortable and disease-free. As the urine evaporates, it cools the vulture's body in the same way sweat works on humans. The acid in the urine simultaneously destroys harmful pathogens from their last dinner.

That acid inside a vulture's body can also be wielded as an effective defense mechanism.

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California Condor

One of the most well-known -- and most endangered -- of the New World vultures is the California condor. The population dipped to a low of 25 known individuals in the 1980s [source: Peregrine Fund]. A federal captive breeding program helped the population rebound, releasing some into the wild as early as 1992. However, the California condor remains classified as endangered with a current population of around 200.

The Vulture's Acidic Stomach

If you find yourself in the rare situation of being able to startle a vulture, resist the temptation. When vultures feel threatened, they have a handy way of reacting: They induce vomiting. As repulsive as it seems, vultures aren't the only members of the avian family to practice defensive vomiting. Herons, gulls and terns are known to do so as well [source: Deng].

To get an idea of how unpleasant vulture vomit is, think back to the last time you ate a sandwich with a lot of onions. You probably brushed your teeth or chewed gum afterward to cleanse your breath of that sour onion stench. Now, consider how terribly your breath would smell if you ate a sandwich made of rancid meat. It would probably be gag-inducing to all who passed by.

Carrion-eating vultures take this scenario one step further when in harm's way. Their defensive vomit is foul-smelling enough to drive away predators. If enemies approach too closely, the high amount of acid in the vomit is strong enough to burn them as well. In a study on whiteback vultures, the pH levels in their stomachs were between a 1 and 2 [source: Houston and Cooper]. That measurement is comparable to gastric and hydrochloric acid from the human stomach and is far more corrosive than acid rain, which has a pH between 4 and 5. It was also more acidic than the stomach contents of other carnivorous birds, including herons and barn owls.

In addition to scaring away predators, the vulture's stomach acid also explains how it survives off its odd diet of rotting meat. Vultures will stay healthy even after eating the carcass of a sick animal. The bird's stomach acid is so powerful that it breaks down the meat quickly, before any pathogens have a chance to infect it. But the acid may not kill bacteria completely as it moves through the body. Vulture feces, for instance, have carried traces of anthrax spores from contaminated animal flesh [source: Saggese et al].

However, while most animals recoil from vulture vomit, bald eagles willingly eat it as part of their diet. They are known to scavenge from other birds' kills and will settle for vulture vomit. When vultures hatch chicks, instead of bringing food into their nests to feed them, the parents regurgitate digested carrion. In light of this, perhaps instead of being known as nature's garbage crew, vultures should carry the title of the ultimate freegans.

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Cristen Conger, Staff Writer

HowStuffWorks 2009

Author’s Note: Why is it a bad idea to scare a vulture?

In all honesty, I wasn't thrilled with the prospect of writing about vulture vomit. The feathered flesh-eaters aren't exactly the cutest winged creatures in the sky, and their dietary habits are somewhat stomach-turning. But learning about vultures' upchuck defense mechanism proved to be a surprisingly fun experience since I ran across a wagonload of fascinating facts that altered my negative perception regarding the birds of prey. First, vultures' taste for rotting flesh serves an important purpose of preventing the spread of diseases and bacteria. They aren't alone in their tendencies to puke on threatening passersby, either; stately herons, gulls and terns also rely on the vomit defense. And without their extremely acidic stomachs, vultures wouldn't meet the employee qualifications for working as Mother Nature's much-needed garbage collectors.

Sources

  • "California Condor." Peregrine Fund. (Oct. 7, 2008) http://www.peregrinefund.org/Explore_Raptors/vultures/cacondor.html
  • Deng, Robert. "Black-naped Tern: Defense Vomiting." Bird Ecology Study Group. April 23, 2008. (Oct. 7, 2008) http://besgroup.talfrynature.com/2008/04/23/black-naped-tern-defense-vomiting/
  • Gross, Liza. "Switching Drugs for Livestock May Help Save Critically Endangered Asian Vultures." PLoS Biology. Vol. 4. No. 3. March 2006. (Oct. 9, 2008) http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1351926
  • Houston, D.C. and Cooper, J.E. "The Digestive Tract of the Whiteback Griffon Vulture and Its Role In Disease Transmission Among Wild Ungulates." Journal of Wildlife Diseases. Vol. 11. July 1975. (Oct. 7, 2008) http://www.jwildlifedis.org/cgi/reprint/11/3/306.pdf
  • Morrison, Dan. "Many Asian Vultures Close to Extinction, Survey Finds." National Geographic News. May 1, 2008. (Oct. 7, 2008) http://news.nationalgeographic.com/news/2008/05/080501-vultures-extinct.html
  • Saggese, Miguel D. et al. "First Detection of Bacillus anthracis in Feces in Free-ranging Raptors from Central Argentina." Journal of Wildlife Diseases. Vol. 43, No. 1. 2007. (Oct. 7, 2008) http://www.jwildlifedis.org/cgi/content/full/43/1/136
  • "Vultures." Peregrine Fund. (Oct. 7, 2008) http://www.peregrinefund.org/Explore_Raptors/vultures/vultmain.html

Vultures: Cheat Sheet

Stuff You Need to Know:
  • We can thank vultures for feeding on the dead bodies of sickly animals and thereby curbing the proliferation of bacteria.
  • Feeding on diseased animals typically isn't a problem for vultures due to their incredibly powerful stomach acid that can break down the meat quickly, before any pathogens have a chance to infect it.
  • You may want to refrain from scaring a vulture, should the temptation ever arise. Here's why: Vultures are famous for inducing vomiting when threatened, and they're not the only members of the avian family to do so.
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