Vultures don't have a good reputation. Which is a bit sad really since they're an important part of the ecosystem: they ensure all that left over meat doesn't go to waste. But our revulsion at the consumption of day-old meat blinds us to the important question – how are they able to eat this stuff without dying from the flourishing bacteria?
Described in Nature Communications, a team led by Aarhus University's Professor Lars Hestbjerg Hansen explains that the answer seems to lie in exceptional gut bacteria. Before we continue, however, we suggest you don't read the following over dinner, unless your own stomach rivals a vulture's for toughness.
The dead animal lying in the sun for too long isn't the only issue here. When vultures find an animal with a hide too tough for their beaks, they take the back way in via the anus. Therefore, the meat they are eating is mixed with a flavoring of feces.
"To investigate vultures' ability to survive eating this putrid cocktail, we generated DNA profiles from the community of bacteria living on the face and gut of 50 vultures from the U.S. Our findings enable us to reconstruct both the similarities and differences between the bacteria found in turkey vultures and black vultures, distributed widely in the Western Hemisphere. Apparently something radical happens to the bacteria ingested during passage through their digestive system,” said Hansen, after the first study of vulture intestinal ecology.
The skin on the vulture's faces hosted 528 species of micro-organisms, Hansen found, but only 76 of these survived in the gut. Dominant among these are Clostridia and Fusobacteria, which the authors note are “widely pathogenic to other vertebrates”
University of Copenhagen PhD student Michael Roggenbuck says, "Our results show there has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest. 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 deadly bacteria - species that would kill other animals actively seem to flourish in the vulture lower intestine."
The authors think vultures have gut bacteria capable of both breaking down the meat they consume and out-competing the microorganisms that would flourish inside other animals if they tried to eat rotting meat.
To understand how much the vulture's intestinal micro-organisms have changed to cope with their unique diet, we will need to learn more about related species. Co-author Gary Graves of the Smithsonian Institution says, "The avian microbiome is terra incognita but 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."