Bicolored Antbird (Gymnopithys leucaspis)
Antbirds:
by David L. Ross, Jr.

The ants fanned out across the sun-flecked forest floor. A thin mass of tiny black forms 10 meters wide and 3 meters across, numbering in hundreds of thousands methodically progressed. This is a swarming legion, over powering all too slow in evacuating their path. So proceeds the day for the army ants, a predaceous horde boiling over the forest floor, invading nook, cranny, stump and burrow, for anything, which their impressive numbers can capture. Arthropods as katydids, crickets, beetles, and spiders crawl, slither, and hop away. Scorpions and spiders are pursued up saplings and tree trunks, they are forced to twig and leaf tip from which they drop in an attempt to escape. The ants follow, and at places it seems to sprinkle ants, which undaunted regroup into a column or swarm. Their catches reward the effort, lines leading back to the bivouac carry the quarry and dismembered portions of larger victims. Many prey items suffer what seems a torturous death. Scorpions seem to wreath with pain arching and twisting till the last bites subdue them. Crickets hop through the swarm and are attacked the instant they land they fall over and kick wildly sometimes to jump to safety, and sometimes to still more ants.


While the ants are the cause, they are only the beginning of the fleeing insects peril. Parasitic wasp and flies hover about the swarm-front in numbers as robber flies look to take entire insects. Such a swarm is often revealed by the loud calls of an interesting group of birds. Most dependable of these are the obligate followers, some so dependable as to be expected at any army-ant swarm. These are the so named "antbirds", and a standout amongst them is the Bicolored Antbird whose stocky form is often perched low above the approaching swarm, head hunched low, eye turned downward towards the hunting ants. This horizontal posture is held patiently often on a vertical perch.

The Bicolored Antbirds seem plagued by twitches and other idiosyncrasies. Indeed many species of birds and other organisms exhibit behaviors which upon first glance seem purposeless outside themselves. But an explanation of the bicolored's twitching habits might be found in their proximity to the aggressive army ants. In fact the ants are often searching or traveling along the very perch upon which the birds have chosen to wait. Perhaps this is why Bicolored Antbirds have developed a jerky foot shuffle where the feet are rapidly slid outward along the perch and then, in the process advancing or potentially bird-biting ants are kicked away. This is also accompanied by a rapid fanning of the tail, which may serve to shake off climbers. For certain though is the business at foot, as a large insect hops away from the ants, the antbirds make quick lunges, and short darting flights to capturing in their beaks the larger of the fleeing insects.