Eating eagles carrion

Delicious carrion: vultures rob eagles

Dublin (Ireland) - Food is ready - vultures seem to think to themselves when eagles discover a carcass. A team of international biologists has now observed that they do not stop at fighting the kings of the skies for their food. The vultures spy on the eagles, which occasionally eat carrion, and benefit from their findings. Then they drive the competition away from the feeding ground by mobbing by pushing down in larger groups. They benefit from two things: First, eagles, with their excellent vision, are better able than vultures to spot carrion from the air. Second, they are better able to break open the carcasses with their powerful beaks. The procurement of food for vultures is thus much more complex than previously thought, write researchers in the journal "Proceedings of the Royal Society B". When looking for food, the scavenging birds use not only information from their conspecifics, but also from members of other species. The researchers hope that knowing these connections could help to protect the threatened vultures more effectively.

"We filmed interactions between eagles and vultures feasting on animal carcasses," says Adam Kane of the School of Natural Sciences at Trinity College Dublin. "Our videos confirm that eagles use their keen eyes to find the carcasses first, while the vultures simply 'scrounge' by following them to the carcasses." as well as the predatory eagle (Aquila rapax) and steppe eagle (Aquila nipalensis) have been observed in the wild in Kenya. Their study is not based solely on this field research, in which they analyzed the arrival times of the various birds in the carcasses. In addition, Kane and his colleagues worked with model calculations.

The temporal data from the videos show that the eagles create the information about a food source. They are therefore regarded as producers. The scavengers, on the other hand, are the users, or also scavengers, of this information. The vultures don't just follow the eagles to a good source of food. At the same time, they take advantage of the fact that the eagles with their strong beaks can easily tear open the skins of the dead animals, for example - which the vultures could not do themselves. So the scroungers just wait until the producers have done the dirty work. Only then do they drive the competition off the dinner table and start eating. "But that doesn't mean that the Eagles are the losers," said Kane. You would arrive earlier and would therefore have the advantage of being able to help yourself first. "Once they have been driven out, they can go hunting again - a strategy that is not available to vultures."

With the help of their model calculations, the biologists were able to theoretically analyze further details of the relationships observed in the field. The game theory model shows that such an imbalance in competition - in which the vultures virtually dominate the eagles on the carcasses - predicts this result, which has developed in evolution. Game theory deals with the economy of cooperation and fraud in the case of competing interests. Another model also suggests that the interactions between the eagles as producers and the vultures as scroungers make the vultures vulnerable when the eagle population declines.

Vultures are a very central part of the ecosystem. While other birds of prey such as eagles do not disdain carrion, but also eat prey they have killed themselves, they feed exclusively on carrion. They use dead and decaying biomass and in some cases also reduce the spread of certain diseases. In order to be able to protect them effectively, as the current study shows, it is necessary to consider the entire ecosystem and include it in protection. "Vultures were once the most common birds of prey in the world, but their numbers have been particularly damaged in recent decades from habitat loss, accidental poisoning and hunting," said Andrew Jackson of College Dublin, co-author of the study. "Our study shows that it is important to consider other species as well when trying to protect vultures." In this case, that means protecting those birds of prey that are there early can help increase the likelihood of that vultures can find enough food to survive.

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