Interspecific competition for cliff ledges on the Magaliesberg between nesting Verreaux’s Eagles and roosting Chacma baboons

Abstract

Animals that share suitable rock ledges located on near-vertical cliff faces are compelled to interact when using this
scarce resource. Because interspecific and exploitative competition for suitable ledges may have a vital influence
on the survival and reproduction of Verreaux’s Eagles (Aquila verreauxii) and Chacma baboons (Papio ursinus),
an investigation into the reciprocal rock-ledge usages by the two species will improve our understanding of this
trait. In this study, we used camera traps stationed at four eagle nests to study interspecific interactions at nest
sites. At the first two eagle nests, no baboons were recorded, and two young birds fledged successfully. At the
third nest, the baboons only slept on the nest once the fledgling successfully left the nest. At the fourth nest, the
eagles did not breed and the birds (eight visits) and baboons (three visits) used the nest interchangeably over a
28-day period. Whereas the cliff-ledge provided a secure nest site for the Verreaux’s Eagles in the breeding season,
for Chacma baboons sleeping on an inaccessible ledge may limit predation by terrestrial predators (e.g. by leopard
Panthera pardus). This alternating usage of cliff ledges suggests that the two species probably co-use this limited
cliffside resource to increase their own fitness.

Keywords: apex predator, Aquila verreauxii, baboon-eagle co-use, competition, exploitative, interference competition, Papio ursinus