Two species of tanagers (Passeriformes: Thraupidae) forage on army ant workers ( Eciton burchellii) carrying immature paper wasps.

Eciton burchellii is a Neotropical army ant that consumes a variety of arthropods captured during swarm raids. Wasp larvae and pupae provide an important food source for E. burchellii, and this ant species is thought to be a major predator on immature wasps in many Neotropical areas. Some birds also prey on wasp brood. Numerous bird species regularly follow E. burchellii swarms but are thought to typically avoid eating army ants. Rather, the birds feed on the arthropods that the ant swarms flush from the leaf litter. I report observations of ant-following birds, the Gray-headed Tanager Eucometis penicillata and the Flame-colored Tanager Piranga bidentata consuming E. burchellii workers that were carrying Polistinae wasp larvae and pupae. It has been suggested that ant-following birds may impose a cost to army ants by consuming arthropods and competing with ants for food resources. Also, it has been speculated that army ants emigrate at night to avoid the loss of their brood to birds, but lack of direct observations of birds attacking ants for their brood makes this claim unsubstantiated. My observations of birds consuming wasp pupae and larvae being carried by E. burchellii are evidence of rarely observed direct stealing of prey and loss of ant foragers to ant-following birds. These observations suggest that birds would also eat the larvae and pupae of army ants if given the opportunity, providing evidence to support the claim that predation pressure may be one factor driving nocturnal emigration. [ABSTRACT FROM AUTHOR]