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.