The Ant-Following Bicolored Antbird
- Just Adventures Panama
- Jan 28, 2017
- 2 min read
Updated: Jun 1
The Bicolored Antbird (Gymnopithys bicolor) is a specialized member of the antbird family (Thamnophilidae), found primarily in the lowland rainforests of Central and South America. It is one of only four species in its genus and is classified as an obligate ant-follower—a bird that relies almost exclusively on army ant swarms to locate prey. Unlike many other antbirds and insectivorous birds that opportunistically forage near swarms, obligate followers such as the Bicolored Antbird obtain the majority of their food by capturing insects and other small arthropods flushed out by the movement of the aggressive army ants.

Army ants (especially Eciton species) form massive, mobile swarms that patrol the forest floor, disturbing and flushing insects, spiders, and small vertebrates from leaf litter and undergrowth. These swarms are a keystone ecological phenomenon in Neotropical forests, providing a resource hotspot that attracts a complex guild of ant-following birds. The Bicolored Antbird is among the most dedicated followers, often competing aggressively for the best positions near the leading edge of the swarm where prey density is highest. This aggressive competition includes vocalizations, physical displays, and sometimes direct confrontations with other ant-followers to maintain prime foraging access.
Remarkably, the Bicolored Antbird rarely forages away from ant swarms, demonstrating a highly specialized foraging strategy that ties its survival closely to the availability and movement of army ants. This obligate relationship has driven a series of morphological, behavioral, and ecological adaptations, such as cryptic plumage for remaining concealed near the swarm, and acute vigilance to detect and track the advancing front of the ants (Willis, 1985). The antbirds often maintain a complex system of dominance hierarchies at swarms, where larger species like the Bicolored Antbird generally dominate smaller ant-following species.
This tight ecological link exemplifies one of the most specialized predator-prey tracking strategies in tropical birdlife, reflecting a co-evolutionary dynamic that has persisted over evolutionary time. The dependency on army ants also means the Bicolored Antbird’s presence and population health can be closely tied to the abundance and health of army ant populations and the integrity of their rainforest habitats.
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Sources:
Willis, E. O. (1967a). The behavior of Bicolored Antbirds. Wilson Bulletin, 79(3), 287–301.
Isler, M. L., Isler, P. R., & Whitney, B. M. (1998). Use of army ant swarms by birds in Panama. The Auk, 115(4), 1069–1073.
Willis, E. O., & Oniki, Y. (1978). Birds and army ants. Annual Review of Ecology and Systematics, 9, 243–263.
Remsen, J. V., Jr. (1984). Community organization of army-ant followers: Effects of ant swarms on bird species abundance and distribution. Ecology, 65(6), 1801–1819.
Willis, E. O. (1967b). The behavior of army ant followers. Ornithological Monographs, No. 5.
Willis, E. O. (1979). The behavioral ecology of obligate army ant-following birds. Wilson Bulletin, 91(3).
Willis, E. O. (1985). Ecology and evolution of obligate ant-following birds. In Neotropical Ornithology (P. A. Buckley et al., Eds.).
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