Vultures live on a diet of rotting meat that would result in severe food-poisoning and death in most other creatures. How they do it is a mystery, but a recent investigation suggests these opportunistic feeders have evolved an extreme stomach to help them cope with their rather severe dietary habits.
When vultures descend upon a meal, they strip the rotting carcasses right down to the bone. If the dead animal's hide is too tough to pierce with their beak, they'll enter into it using other, uh, passages — including the rear door (so to speak) via the anus. Consequently, their diet often consists of meat that's not only rotting, but also laced with fecal contaminants that would kill most other animals. These birds, which include turkey vultures and black vultures, are somehow immune to the deadly cocktail of microbes contained within their dinner, included Clostridia, Fuso- and Anthrax-bacteria.
To find out how they do it, a team of international researchers generated DNA profiles from the community of bacteria living in the face and gut of 50 vultures from the United States. This allowed the researchers to reconstruct the differences and similarities between the bacteria found in vultures throughout the Western Hemisphere. Their analysis shows that something radical happens to the bacteria as it's being ingested and as it travels through the vultures' digestive system.
On average, the facial skin of vultures contains the DNA of about 528 different types of microorganisms, whereas the gut only contains about 76 types. This suggests that the vast majority of microbes are somehow being killed en route to the gut and/or on arrival, but that a good portion still survive the process and don't appear to harm the vulture.
"Our results show there has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest," noted team member Michael Roggenbuck in a statement. "On 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 bacterial toxins — species that would kill other animals actively seem to flourish in the vulture lower intestine."
By deadly bacteria Roggenbuck is referring to the Clostridia and Fusobacteria. The researchers say it's possible that these particular microbes are simply out-competing the other bacteria in the gut. It's also possible that they're conferring some benefit to the birds. The researchers suspect it might be a bit of both; while other microorganisms are likely out-competed by the surviving bacteria, the vultures also receive a steady stream of important nutrients when the bacteria break down the carrion.
The finding suggests that vultures (and probably many other birds) have evolved a rather complex and intimate relationship with their gut bacteria. And indeed, the DNA of prey species were completely degraded in the gut samples taken from most vultures, suggesting that the gastrointestinal tracts of vultures are extremely selective.
Read the entire study at Nature Communications.