How Can They Eat That?

factorialist_carrion

Have you ever had a case of food poisoning? The terrible headache, alternating fever and chills, the crippling cramps which lead to diarrhea and vomiting…it’s not an experience you’re likely to forget. It’s definitely not one you’d want to repeat.

factorialist_microbeAs you probably know, food poisoning is caused by consuming food that is spoiled, undercooked, or improperly cleaned. Such food can be contaminated by viruses or bacteria, like staphylococcus, E. coli or salmonella. These microbes, while common, wreak havoc when ingested, and the symptoms we experience are the body’s way of purging them from our system.

Will That Be Dine In, or Carrion?

Amazingly, there are members of the animal kingdom which survive on food that would make us miserably ill: uncooked and contaminated meat. I’m talking about scavengers, or carrion eaters, of course. Vultures, hyenas, crows, and coyotes are some well-known examples, but many more exotic species like the Komodo dragon and Tasmanian devil also survive primarily on dead meat. Other animals not typically portrayed as scavengers, like bears, foxes, lions, and badgers, will not turn up their noses at carrion.

“Scavengers are found in nearly any climate, and are an important part of every ecosystem”tweet

Scavengers are found in nearly any climate, and are an important part of every ecosystem; they clean up the remains of the dead, and keep valuable nutrients in circulation.

But the question remains: How can they eat that? Why don’t they get sick like we do?

The answer is somewhat complex.

For one thing, their digestive systems have evolved to be highly acidic, and thus more capable of breaking down raw meat and the bacteria that so often accompany it. This is true not just for scavengers, but for carnivores in general. Whereas we humans have inherited the digestive tract of our largely herbivorous ancestors, which is more suited to dissolving cellulose and fibrous plant matter.

Also, most carrion eaters don’t actually prefer their meat rotten. They actively seek out fresh corpses, in which the flesh has not yet reached an advanced state of decay. The toxic and harmful bacteria are often found in the deceased animal’s intestines and colon, or in the surrounding soil. The longer the body is left lying in the open, the more the internal organs break down, and the more those bacteria are able to spread and contaminate the surrounding muscle tissue.

A Bacteria Battle Rages on in the Belly

All but the toughest scavengers avoid rancid corpses, where the meat is badly decomposed. And, following that line of reasoning, I guess you can call vultures the toughest of the tough. They can, and often do, consume meat that is so rotten and riddled with bacteria that it would be deadly to most other species.
the destructive power of their gastrointestinal juices
A group of scientists from Denmark recently undertook a study of the digestive system of the North American vulture; the results were published in the journal Nature Communications.

The team took samples from 50 different vultures, from two different species, comparing the bacteria from their faces, their guts, and their feces. They found that bacteria were much more prolific on their faces and beaks than in their digestive tract (528 different strains, as compared to just 76), suggesting that their strong stomachs are capable of dissolving and breaking down most microbes.

The team also noted the complete breakdown of DNA in the vulture’s gut, as compared to samples taken from its face and food, further demonstrating the destructive power of their gastrointestinal juices.

factorialist_botulismHowever, some bacteria do proliferate in the vulture’s digestive system, and they are definitely not the kind of microbes you would want hanging around in your stomach. The study found that the vultures’ guts were full of Clostridia and Fusobacteria, both of which are highly toxic to humans – and most other vertebrates, for that matter.

Fusobacterium is known to cause ulcers and sepsis. It flourishes in cancerous cells and tissues (whether or not it actually causes cancer has not yet been determined). Clostridia are a colorful group of pathogens which are responsible for such conditions as tetanus, botulism, gangrene, and – you guessed it – food poisoning.

But these nasty little germs make themselves right at home in the guts of vultures, forming a mutually beneficial partnership, or symbiosis. The bacteria get a constant supply of dead flesh upon which to feed, and in return they help the vultures to break down meat that is…well, less than fresh. This arrangement is one of the key ways that vultures have evolved to be the perfect scavengers, filling an important niche in ecosystems around the world.

You know what they say: it’s a dirty job, but someone’s gotta do it.