In the Pyrenees, where several vulture species may gather at a single carcass, the bacteria inside their bodies behave in ways quite unlike what one might expect. A new study led by the CSIC Institute of Pyrenean Ecology has shown that each of the four European species — the bearded vulture, the griffon vulture, the Egyptian vulture and the cinereous vulture — forms its own unique microbiome, even when the birds share the same carcass.
The researchers analysed samples from 155 wild birds at four body sites: the face, the beak, the trachea and the cloaca. Bird species explained 18 % of the differences in microbiome composition, whereas body site explained only 9 %. This means that “who you are” matters more than “where you are sampled”. The red kite, which does not feed exclusively on carrion, also displays its own species-specific pattern.
The microbiome is not merely a collection of bacteria but a whole ecosystem involved in digestion, detoxification and defence against pathogens. Until now, such communities in scavengers had hardly been studied in natural conditions. It is now clear that mere contact with the same bacteria on a carcass does not guarantee their establishment in the body. Each species decides for itself which microbes get to stay.
This discovery is especially important for Spain, which is home to the largest vulture populations in Europe. Samples were collected from 2017 to 2022, mainly in Aragon, as well as in Catalonia and the Basque Country. In young birds the microbiome is even poorer than in adults: the community forms gradually, as the birds switch to carrion. Sex, meanwhile, has almost no effect.
The practical value of the study is considerable. By tracking changes in these bacterial communities, it will be possible to detect health problems in birds earlier and to understand how they are affected by the food supply, age or the environment. Moreover, vultures continue to perform their ancient role as nature’s sanitarians, quickly removing carcasses and thereby curbing the spread of dangerous microorganisms.
The next step is to understand exactly what functions these species-specific bacteria perform and whether they can be used as indicators of population status.
