The early bird gets the carcass: Temporal segregation and its effects on foraging success in avian scavengers

Temporal segregation is known to be an important mechanism of coexistence in many foraging guilds but has not been examined in avian scavengers. Given that carrion availability is higher in the morning than in the afternoon and that differences in wing-loading and nesting behavior may limit morning activity in some species, there is potential for temporal segregation in resource use to play an important role in the coexistence of avian scavengers. I predicted that Lappet-faced Vultures (Torgos tracheliotos), which have lower wing-loading and lower competitive abilities, would have higher abundance at carrion resources in the morning than White-backed Vultures (Gyps africanus) and Ruppell's Vultures (G. rueppellii). In addition, I predicted that differences in activity patterns among vulture species would affect foraging success. Using experimental carcasses, I examined the effect of time of day on foraging behavior. I quantified foraging success in roosting birds, measured as the proportion of individuals with a full crop. Contrary to predictions, during the dry season White-backed and Ruppell's Vultures were more abundant at carcasses in the morning and Lappet-faced Vultures were more abundant in the afternoon. In the afternoon a large proportion of the Gyps individuals appeared to be satiated and densities were lower at carcasses, perhaps creating a temporal competitive refugium in the afternoon during which Lappet-faced Vultures could feed. However, Lappet-faced Vultures have lower foraging success than White-backed and Ruppell's Vultures. These results demonstrate that temporal segregation occurs, but may not reduce competition, in this scavenging guild.