Red-throated Caracara, a falconid raptor, rivals predatory impact of army ants on social wasps

Abstract

Paper wasps are diverse in Neotropical rainforests but the factors that affect their abundance are poorly understood. Army ants (Ecitoninae) are generally thought to have the greatest predatory impact on populations of social wasps, but there is emerging evidence that predatory birds could also be a significant source of colony mortality. Our objectives were to (1) identify the genera of wasps preyed upon by Ibycter americanus (Falconidae), a specialist predator of Neotropical social wasps, (2) quantify wasp nest predation by I. americanus, and (3) compare wasp nest predation rates by I. americanus with calculated rates of wasp nest predation by Eciton burchellii army ants. In 2008 and 2009, we video recorded chick provisioning at I. americanus nests in French Guiana and found that adult birds brought nests of at least ten genera of mainly swarm-founding wasps (Epiponini). In 2012, we noted that three of four sympatric Eciton species raided into trees and thus potentially preyed upon the brood of paper wasps at the same site. We quantified the population density of one Eciton species, calculated its rate of wasp nest predation, and compared this predation rate to that of I. americanus. We conclude that I. americanus rivals the predatory impact of E. burchellii army ants on some populations of Neotropical social wasps. Ibycter americanus and other diurnal vertebrate predators may exert strong selection on wasp defensive behavior, resulting in defensive adaptations that include selection of specific nest sites as well as physical fortification and visual crypsis of nests.