Ant colony tracking in the obligate army ant-following antbird Phaenostictus mcleannani

Abstract

More than 100 species of tropical birds track army ants to feed on arthropods that flee from the ants. Some species are obligate ant-followers that obtain most of their food at ant swarms, but the mechanism used to track ant colonies remains poorly understood. Ant colonies are nomadic and do not raid every day. It has been hypothesized that (1) by keeping track of three ant colonies daily, each bird should find at least one ant swarm per day, and (2) the birds use the vocalizations of conspecifics as cues to find ant swarms. I followed radiotagged Ocellated Antbirds (Phaenostictus mcleannani) in Costa Rica, which are obligate army ant-following birds, to test both hypotheses and describe how they navigate to find army ant swarms. I found that the birds remained at a single ant swarm throughout the day if that swarm was found in the dominance area of the birds; otherwise, the birds visited several ant colonies. Birds travelled in an oriented manner among ant colonies, in cohesive groups that moved in single file. I recorded “following” events in which a focal bird travelled in a group to a nomadic ant colony that this bird did not check on the previous day; the focal bird travelled with birds that visited the colony on the previous day. Following was occasionally facilitated by vocalizations produced by birds immediately before leaving a swarm. I propose that individual Ocellated Antbirds take advantage of collective knowledge to find army ant swarms.