Vultures eat all kinds of nasty stuff that humans can't (and wouldn't if we could). But how do they survive living off the rotting flesh of roadkill? Researchers set out to answer that query by examining the guts of 24 turkey vultures and 26 black vultures trapped and killed in Tennessee. Expecting to find plenty of bacteria as in human intestines, scientists were surprised to find ... poisons. The first, fusobacteria, is known to cause blood infections in humans, while the second, clostridium, "produces deadly botulism toxins," NPR reports. In vultures, the poisons appeared ineffective. Researchers also found "harsh chemical conditions" inside the birds' gastrointestinal tracts, LiveScience reports; vulture stomach acid is anywhere from 10 to 100 times stronger than that of humans.
Scientists guess the vultures' "extremely tough" digestive systems developed an immunity to the toxins, which may in turn help break down other nasty bacteria during digestion. "I think it's mind-boggling that organisms that are perceived as very bad for you seem to be very useful for other biological creatures," a researcher says. "It is not unreasonable to suppose that the relationship between birds and their microbes has been as important in avian evolution as the development of powered flight and song," another adds. The Washington Post reports vultures help kill dangerous microbes before they pass back into the ecosystem, and adds that understanding their immunity could help humans fight our own bacterial infections. (Click to find out what scientists learned about vultures when they left human bodies to decompose in a field.)