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Following birds that follow army ants

Aaron Maizlish/Flickr.comOcellated antbirds make their living off army ants.

As a child I was traumatized by a movie that featured hordes of army ants shredding every living thing in their path. Entire villages of people, dogs and livestock were stripped to skeletons.

OK, traumatized may overstate matters a bit, but I still remember the movie quite clearly after all these years. I’m not sure how many years, but the movie was in black and white.

I have since learned there is nothing for people to fear. For scorpions, centipedes and other ants, it’s a different matter. Indeed, when I visit the tropics, I look forward to finding raiding columns of army ants with great anticipation. It’s not that I enjoy watching the ants dismember grasshoppers and cart the butchered pieces back to the temporary bivouac. Rather, it’s the unique set of birds that have come to capitalize on the frenzied escape of insects. They have found it advantageous to wait around the margins of these swarms and pick off the invertebrates trying to flee.

The list of birds that are army ant specialists is long. A field guide to birds of any tropical country in the New World from Mexico south will have pages devoted to antbirds, antthrushes, antwrens, antshrikes, antvireos, antpittas and more. Most are from a family of birds (Formicariidae), and almost all follow army ants.

The family name is derived from the Greek word for “ant.” They are not actual wrens, shrikes and vireos, but they simply reminded scientists of familiar species from home. And then there are others including tanagers, woodcreepers, woodpeckers, cuckoos and even a few raptors that benefit from the food bonanza.

To find an army ant swarm is to find a wide range of bird species. Many are seldom encountered anywhere else in the forest. The birds at army ant foraging columns tend to ignore people. You can approach relatively closely and observe these birds as they wait patiently maybe a foot off the ground for the opportunity to snatch a fleeing insect. A person can safely approach an army ant column within a foot. Just don’t step on the foraging column. The ants do bite and sting.

Two of my favorite antbirds are spotted and ocellated antbirds. The ocellated antbird has blue skin around the eye and is covered in chestnut-colored feathers, each with a black central spot.

Unlike many ants, the several species of army ants do not make permanent nests. As they scour the forest floor, there is little left behind for the ants (or the birds) to feed upon. The ants must constantly move to new areas that have had the opportunity to repopulate the forest floor with a new crop of insects since the last visit. Consequently, they establish temporary nests to house eggs, young and pupae. These bivouacs are formed by the bodies of the living ants. Periodically, they must disassemble the temporary home and move.

This makes me wonder how the birds that are army ant specialists raise young. They must return to their own nest to feed nestlings, and their nests are not mobile like those of the ants. How do they relocate the traveling ant swarm? How far can they commute from swarm to nest? How do they find a new swarm when one swarm leaves their home range?

Stewart Janes is a retired biology professor at Southern Oregon University. He can be reached at janes@sou.edu.