It takes special guts to be a vulture, scientists said Tuesday, as they explained a long-standing riddle of the animal world.
The birds strip putrid carcasses to the bone -- and if the hide is too tough to pierce with their beak, they will happily rummage their way to the innards via the anus.
In doing so, vultures expose themselves to toxins and microbes like anthrax and clostridium that would sicken or kill other animals.
The bird's trick lies in an extraordinary digestive system, according to a study by Danish and US scientists published in the journal Nature Communications.
Honed by millions of years of evolution, the vulture gut enables the creature to kill most of the harmful bugs it swallows, and cosily co-exist with the remainder.
The scientists generated DNA profiles of bacteria communities living in 50 American vultures -- 26 black vultures (Coragyps atratus) and 24 turkey vultures (Cathartes aura).
Samples taken from the vultures' facial skin showed a massive variety of 528 different types of micro-organisms. But only 76 survived in the gut.
"Our results show that there has been strong (evolutionary) adaptation in vultures when it comes to dealing with the toxic bacteria they digest," said Michael Roggenbuck of the University of Copenhagen.
"On the one hand, vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest.
"On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria -- species that would kill other animals actively seem to flourish in the vulture lower intestines."