For bird enthusiasts visiting the lowland rainforests along the Madre de Dios River in eastern Peru, experiencing an army ant swarm is one of the most exciting spectacles. Following a raiding column of Burchell’s Army Ant (Eciton burchellii) not only reveals the fascinating behavior of these relentless predators but also provides a rare opportunity to observe a diverse assemblage of ant-following birds in action.
To find a swarm, you must first identify the right habitat. The forests of Tambopata National Reserve and Manu National Park provide prime conditions for army ant activity. Early morning is the best time to search, as swarms typically begin their raids shortly after dawn. Instead of looking for the ants directly, it is more effective to listen for the calls of obligate ant-following birds, such as the Ocellated Antbird (Phaenostictus mcleannani) and the Bicolored Antbird (Gymnopithys bicolor), which rely on the swarms to flush out insects.
Tracking a swarm requires patience and attention to bird behavior. The most dominant species, including the White-throated Antbird (Gymnopithys salvini) and the Bare-crowned Antbird (Gymnocichla nudiceps), position themselves at the leading edge of the swarm to capture the most abundant prey. Other specialists, such as the White-plumed Antbird (Pithys albifrons), forage slightly behind the front line, taking advantage of insects that escape the initial assault. Opportunistic species like the Spotted Antbird (Hylophylax naevioides) and Rufous-capped Antthrush (Formicarius colma) often follow at a distance, picking off stragglers.
Once you locate a swarm, positioning is crucial. Standing too close may disrupt bird activity, while stepping into the ants’ path can lead to painful bites from their aggressive soldiers. These Eciton burchellii defenders use powerful mandibles to subdue prey and will not hesitate to latch onto anything they perceive as a threat. Wearing long pants and being mindful of your footing will help avoid unwanted encounters.
Understanding the ants’ behavior increases your chances of success. Eciton burchellii colonies alternate between raiding and stationary phases, with active hunting lasting up to two weeks before transitioning into a bivouac. Arriving during the stationary phase may yield little more than a cluster of resting ants and no bird activity.
Occasionally the Plumbeous Antbird (Myrmelastes hyperythrus) follows army-ant swarms in pursuit of prey flushed by the ants. Prey usually perch-gleaned by reaching up, out or down with quick stabs of the bill. Observed to pick large larvae 5–8 cm long from fallen tree trunks; in order to consume these, pecked off pieces a third the size of the bill, sometimes biting pieces off ends.
Experiencing an army ant swarm along the Madre de Dios River offers an unparalleled look into the intricate relationships that define tropical ecosystems. The interplay between ants, birds, and fleeing insects is a dynamic and unforgettable spectacle, rewarding those who take the time to observe and appreciate it.
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