Last Sunday we had an excellent encounter with an army ant swarm and ant-following birds right on Pipeline Road. Ant-following behavior in birds is most often encountered in the Neotropics where diurnal ant swarms scour the forest floor for arthropods and small vertebrates.
Ant-following birds actually act as kleptoparasites, ant swarms have been found to have greater foraging success when birds were excluded (Wredge et al. 2005. Ecology 86:555–559). Obligate ant-following species, such as the Ocellated Antbird, are noted for bivouac (think giant ball of army ants clinging together, because that’s pretty much exactly what we’re talking about) checking, where every morning the bird visits several ant colonies in search of an actively raiding group. This behavior is mostly seen in obligate species, but has been observed in opportunistic species in areas without obligate ant-followers (O’Donnell et al. 2010. The Wilson Journal of Ornithology: 122(3), 503-512).
We encountered three of the antbirds at the swarm. An obligate follower the Ocellated Antbird which has gone extinct from BCI, the Bicolored Antbird- also an obligate ant follower, and an opportunistic follower the Spotted Antbird. Spotted Antbirds on BCI, where the dominant Ocellated Antbirds are now absent, have increasing attendance at swarms and home ranges that overlap more than those of Spotted Antbirds on the mainland (Touchton and Smith. 2011. Ecology 92:1126–1136.).
In addition to the antbirds, the swarm we encountered was attended by gray-headed tanagers, song wrens, a white-whiskered puffbird, several species of woodcreepers, a broad-billed motmot, and several other species.
We were lucky to witness an army ant swarm so close to the road, hopefully we’ll encounter another during this course!