Let someone else do it! That’s the attitude taken by hungry hyenas and jackals on the plains of Kenya in their search for food. Rather than finding a meal by themselves, they often look to the skies in order to spy on the movements of vultures.
When large groups of these iconic birds descend, they present an obvious signal to a carcass, which the mammals cue to. They are, in effect, the eyes in the sky for the mammals. This is a shrewd behaviour because the view of animals stuck on the ground is often blocked by the lay of the land.
A team of biologists from North Carolina Zoo and University College Cork recently published their findings in the Journal of Animal Ecology having used a combination of fieldwork and computer modelling to show that by using vultures, hyenas and jackals could find carcasses nearly twice as fast as if they had to search without them. One of the authors — Dr Adam Kane of University College Cork, who began this work at Trinity College Dublin — previously showed that vultures themselves often scrounge on the discoveries of eagles.
Dr Kane said: “What we’re seeing is a chain of arrivals at a carcass where the species that arrive early on tend to be the best spotters, whereas those that arrive later tend to be the most physically dominant. This is important because it means the first-comers must eat quickly before they are bullied off their dinner.”
“Although both jackals and hyenas are capable hunters, a carcass doesn’t fight back, so the mammals don’t have to work as much as they would for a hunt. They have an army of vultures to contend with but a vulture is quite a bit smaller than your average hyena. The birds can’t afford injuries if they are to ever fly again, and so tend to concede their meals to the larger competitors.”
By building computer models that used real-life animal data, the authors were able to predict the time that mammals should arrive at a carcass if they were cuing to the arrival of the birds.
Dr Kane added: “We know how far a hyena can see and how fast it can move so it’s simple math to determine when it should appear at the carcass if it is indeed following the descending vultures.”
Co-author Corinne Kendall, who conducted the fieldwork in the Masai Mara National Reserve, said: “Curiously, the mammals never directly followed scavenging eagles. Eagles have a broad diet and also eat small prey, like snakes and mice, and thus they may not be a reliable signal when searching for larger carrion that mammals are actually looking for.”
Unfortunately, all African vulture species are on the edge of extinction. The results from this study suggest that as vultures disappear from the environment there could be negative impacts on the mammals who need a cue from above to find carrion.
Additionally, vultures provide an important ecological service in keeping diseases outbreaks down, so their dwindling numbers may coincide with unwelcome spikes of diseases like rabies, which can proliferate on rotting carcasses and be spread rapidly by animals eating the older, rotten meat. That’s why North Carolina Zoo, in partnership with the Wildlife Conservation Society, has an on-going program to save vultures in Tanzania.