Red-throated Caracaras are enigmatic but seldom studied raptors of tropical American forests. They are known to prey on social wasps and exhibit cooperative breeding, but little quantitative data have been published. We investigated Red-throated Caracara nesting, predation and social behaviour in the field in French Guiana from 2008 to 2013. We closely studied two nests with automated camera systems and found a high level of cooperative behaviour among adults tending nests. Seven individuals were involved in bring prey to and guarding a nest in 2009. Our observations of caracaras nesting in bromeliads confirmed that the majority of their diet was comprised of the brood of social wasps, although they also brought millipedes and fruits to the nest. The social behaviour of the caracaras included intense territorial behaviour, including specific vocalizations and displays in response to conspecifics or playback of caracara calls. Caracaras also attacked conspecific decoys, and we observed them attacking members of other groups on two occasions in 2011. The caracaras provided their chicks with nests of a diverse assortment of wasp genera, including Polybia, Pseudopolybia, Leipomeles, Apoica and Parachartergus, and the proportional abundance of these taxa is not congruent with published studies on generic abundances. In addition, while army ants had previously been considered top predators of social wasps, we calculated that the caracaras, as specialist predators, could rival or exceed army ants as a mortality factor for social wasps. It had been hypothesized that these caracaras rely on a powerful chemical repellent to protect themselves from the stings of their defensive prey, but we found no evidence of such a repellent. We used a video recording arena to observe caracara predation behaviour on nests of various species of Polybia. We observed that the caracaras are indeed stung by some species of wasps, but the caracaras mount high-speed aerial strikes against such nests, knocking them to the ground or striking them repeatedly until the adult wasps depart in an absconding swarm. The caracaras exploit this absconding response when attacking highly defensive wasp species in order to minimize stings while obtaining the wasp brood.
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Thesis advisor: Gries, Gerhard
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