Research undertaken in Kenya, by zoologists from Trinity College Dublin, has revealed that vultures of the Gyps species are acquiring and using social cues from keen-eyed raptors to pinpoint carcass location. The vultures are then plundering the raptors’ finds, displacing the eagles, and reaping the rewards of their raids.
Gyps vultures are reliant on thermals to fly; flapping flight is too energetically expensive to allow them to cover a large enough area to be effective scavengers. Raptors also exploit thermals, but due to their smaller size they are able to utilise the relatively weaker, early morning thermals. This leads to raptors encountering carrion ahead of the vultures.
The scientists used game-theory models and fieldwork collected from the Mpala research centre in the Laikipa district of Kenya to study producer-scrounger dynamics between species of scavenging avifauna. Not only were the vultures utilising the eagles’ eyesight, they were also benefiting from their sharp, hooked beaks. Eagles are far better equipped than vultures when it comes to having the tools to pierce and tear into the tough, leather-like hide of an ungulate.
African white-backed vultures (Gyps africanus) and the Rüppell’s vultures (Gyps rueppellii) were observed delaying raiding the raptors bounty until the tawny (Aquila rapax) and steppe eagles (Aquila nipalensis) had ripped through the hide. The marauding vultures then converged en masse, to out-muscle and force the raptors from the carrion.
The researchers suggested that the eagles were not losers in these interactions, gaining a “finder’s fee”- an exclusive share of the resource by arriving first at a carcass, before continuing to hunt throughout the day.
It is believed that these findings could have positive ramifications when it comes to considering strategies regarding vulture conservation. Vultures are an ecologically vital group of birds due to their keystone role as obligate scavengers and biomass recyclers.
Vulture numbers are declining severely in many of their ranges. Both the African white-backed and the Rüppell’s vulture are IUCN red-listed as endangered and have faced rapid declines in population numbers. This study underscores the importance of shifting conservation efforts to eco-system based management strategies as opposed to centring attention on single species.
In a press release, Dr Andrew Jackson from Trinity College Dublin, who supervised the research, stated that “Vultures were once the most abundant birds of prey in the world, but their numbers have been hammered in recent decades by habitat loss, inadvertent poisoning, and hunting. Our study shows, as is often the case in the tangled web of ecology, that it is important to consider other species when trying to conserve vultures. Conserving early rising raptors may help to boost the chance that vultures find enough food to survive.”
A. Kane, A. L. Jackson, D. L. Ogada, A. Monadjem, L. McNally. Vultures acquire information on carcass location from scavenging eagles. Proceedings of the Royal Society B: Biological Sciences, 2014; 281 (1793): 20141072 DOI: 10.1098/rspb.2014.1072