Scouts vs. usurpers: alternative foraging strategies facilitate coexistence between neotropical Cathartid vultures

Abstract

Understanding how diverse assemblages of scavengers can coexist on shared ecological resources is a fundamental challenge in community ecology. However, current approaches typically focus on behaviour at carcass provisioning sites, missing how important differences in movement behaviour and foraging strategies can facilitate sympatric species coexistence. Such information is particularly important for vultures – obligate scavengers representing the most endangered avian foraging guild. Their loss from ecosystems can trigger trophic cascades, mesopredator release and disease outbreaks. We provide the first-ever analyses of GPS location data from wild King Vultures Sarcoramphus papa and Greater Yellow-headed Vultures Cathartes melambrotus, coupled with trait data (from both wild-living and museum specimens) and visitation data from camera traps deployed at provisioned carcasses, to characterize vulture flight behaviour and strategies in the Peruvian Amazon. We found marked species differences in several key movement characteristics, including: King Vultures having home-ranges five times larger, average flight heights four times greater and ground speeds 40% faster than those of Greater Yellow-headed Vultures. Despite these differences, both species flew similar distances each day (on average), probably due to King Vultures taking 50% fewer flights and spending 40% less time in the air per day. Consistent with these patterns, King Vulture body mass was more than double that of the Greater Yellow-headed Vulture, with a substantially larger hang wing index (a measure of long-distance flight efficiency). At carcasses, Greater Yellow-headed Vultures typically arrived first but were rapidly outnumbered by both King and Black Vultures Coragyps atratus. We find that the movement behaviour of obligate apex scavengers in the western Amazon is linked to their ability to coexist – Greater Yellow-headed Vultures, a smaller stature ‘scouting’ species adapted to fly low, forage early and arrive first at carcasses, are ultimately displaced by larger-bodied, wider ranging King Vultures at large ephemeral carrion resources. Expansion of future GPS tracking initiatives could facilitate the exploration of direct facultative interactions from animal movement data and give further insight into how diverse communities assemble and interact.