Vultures look at eagles

Scavengers use eagles as "feed scouts" to find fresh carcasses

An African vulture approaching © Darcy Ogada
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Flying Snorkels: African vultures use eagles as "feed scouts" and let them do the tedious search for carrion. They observe the eagles on their flights and wait until they have discovered a carcass and have already broken up ready to eat, as British biologists discovered. But that means: If the eagles disappear in one area, the endangered vultures also suffer.

As scavengers, vultures are virtually the flying disposal force of nature - and this is very effective. For when a vulture has spotted a carcass, other people quickly find themselves. "In flight, they keep visual contact with their conspecifics. Then when someone discovers a carcass and lands, the others notice it quickly, "explain Adam Kane of Trinity College Dublin and his colleagues. In their study, the researchers now want to find out if vultures can also "look" across species, where a rewarding meal can be found.

Dead ungulates as "bait"

For this purpose, the researchers exposed carcasses of dead ungulates near the Makpala Research Center in Kenya. In addition to the white-backed vulture (Gyps africanus) and the black-billed monkey (Gyps rueppellii), two eagle species live in this area - the steppe eagle (Aquila nipalensis) and the savanna eagle (Aquila rapax). The two eagle species usually hunt live prey, but do not disregard carrion if they happen to find it.

With the help of surveillance cameras, the researchers filmed which birds first discovered the designed carcass and how quickly a representative of the other bird group was there. Even those who initiated and then won the ensuing conflict examined the researchers on the basis of the images.

Most of the eagles spotted the carcass first, only then came the vultures. © Darcy Ogada

Vulture as "Schnorrer"

The result was clear: In most cases, one of the two eagle species first arrived at the carcass, followed immediately by the first vulture. This was so quickly on the spot that this can not be a coincidence, as statistical evaluations revealed: The vultures must have followed the eagles deliberately. "Our videos confirmed that the eagles use their keen sight to find the carcasses, while the vultures simply snoop on this information and follow them to the carrion, " explains Kane. display

And not only that: At the set table, the vultures wait until the eagles have torn open the carcass with their beaks. Only then do they press close and try to drive the eagles off the prey usually with success. Although the biologists observed the reverse case a few times, that an eagle followed a vulture, but much more often the vultures were the "scroungers".

Problem updrafts

The reason for this is obvious: The big vultures need thermal updrafts to fly through the air, as the researchers explain. But just in the morning, these updrafts are still rare. In order to be able to fly off a large area, they would have to change to flapping flight and that costs a lot of energy. Eagles, on the other hand, use a different flying technique and can therefore fly off large areas without updrafts.

"Therefore, it is very likely that they will discover a fresh carcass before the vultures, " said Kane and his colleagues. The vultures, on the other hand, seem to have learned not only to peer from their peers, but also to closely observe the eagle behavior and to recognize when they have found the carrion.

Important for vulture protection

"Our results show that a social transfer of information can lead to important interactions between different species, " say the researchers. The endangered vultures must therefore not only be regarded and protected as an isolated species, but other species must also be considered - in this case the eagles. Because if these disappear or are hunted too hard, the vultures suffer as well: they lose their most important food scouts. (Proceedings of the Royal Society B: Biological Sciences, 2014; doi: 10.1098 / rspb.2014.1072)

(Royal Society / Trinity College Dublin, 10.09.2014 - NPO)