Why vultures are not poisoned by carrion

Some of the most mysterious species of fauna are scavengers. These animals feed on decaying organic material, or, more simply, the corpses of other animals. And at the same time, cadaveric poison does not affect them. The task of scavengers is important and even partly noble: they serve as an important link in the processing of organic matter, make it more accessible to microorganisms, and, in addition, eliminate potential breeding grounds for infectious diseases.

Today we'll talk about one of the brightest representatives of scavengers - vultures.

Vultures often deal with decaying remains that contain both highly unsafe bacteria and the cadaveric venom they produce. It is believed that the characteristic features of the appearance of scavengers are adaptations to a specific diet: a long, flexible neck allows them to "examine" the insides of a fallen animal in detail, and the absence of feathers on the head and neck reduces the likelihood that food pieces with bacteria and putrid juices linger on the body birds. As for the famous down or feather collar, it literally serves as a napkin - so that everything that flows down the scavenger's neck does not flow further onto the chest, back and stomach. Let it linger on a small "napkin" than stain the whole body. Well, in order to get rid of the bacteria that nevertheless got on them, the birds take sun baths: they spread their wings, exposing themselves to the sun's ultraviolet light (presumably, such disinfection works most effectively in the mountains).

But scavengers need to protect themselves not only from the outside, but also, so to speak, from the inside - after all, their digestive system must somehow resist putrefactive bacteria and decomposition products. On this score, there are various hypotheses, partly confirmed by research. For example, the resistance of birds to bad substances is explained by the strong acidity and powerful enzymatic activity of the gastrointestinal tract (it is known that vultures and vultures easily digest bones). On the other hand, bacterial microflora can play a role here.

Scientists from the University of Copenhagen (Denmark), Copenhagen Zoo and the Smithsonian Institution (USA) analyzed which bacteria live in two species of vultures, came to the conclusion that the gastrointestinal tract of birds combines high destructive power with no less high selectivity. The most amazing thing is that the vultures managed to "make friends" with the bacterial genera Fusobacteria and Clostridia. Some fusobacteria are part of the normal microflora of the upper respiratory tract, gastrointestinal tract and genital tract, but some of them are involved in the processing of organic remains. The same applies to clostridia - some of them are generally poisonous, producing botulinum toxin and other poisons. Largely due to fusobacteria and clostridia, animal remains become inedible for most animals. In addition to vultures: in them, these microbes have become a normal component of microflora, apparently helping the birds to digest carrion.

Another curious detail was revealed when they decided to compare the microflora of scavengers living in the wild with those that live in zoos. Both eat differently, and one would expect that their microflora will be different. Indeed, as we know, the diet strongly influences the species composition of gastrointestinal bacteria, at least in mammals. Since vultures and ordinary birds of prey are fed in the same way in a zoo, the bacteria in their intestines should be similar. But everything turned out to be different: in vultures in the zoo, the microflora resembled that which could be found in vultures in the wild, rather than in owls and hawks from neighboring cages. In other words, in scavengers, the composition of gastrointestinal bacteria is determined not so much by the diet as by the digestive system itself. The research results are published in Nature Communications.

How exactly the stomach and intestines of vultures separates unnecessary bacteria from the necessary ones, and how the necessary bacteria, despite all their harmfulness, help birds digest carrion is not yet completely clear. However, it is obvious that the relationship between scavengers and microflora is much more complex than previously thought, and new work indicates the directions in which these relationships can be studied. Indeed, the chemical environment of the stomach of vultures is unfavorable for many bacteria, but we managed to establish fruitful cooperation with some of them (more than dangerous). In general, the gastrointestinal bacteria of birds have been studied much, much worse than their "counterparts" in animals and humans, so, most likely, in the future, not only vultures with their eccentric feeding habits, but also ordinary birds will receive increased attention.