Army Ants and Birds
There are more than 150 species of army ants in the Neotropics and they forage in large swarms on the forest floor. The ants flush out cryptic arthropods and other small vertebrates that attempt to escape the swarm.
During an army ant swarm, it is common to observe flocks of different bird species and other critters including lizards, following army ants. But why do birds, especially, follow army ants? Well, there are two possible reasons for this.
A behavioral ecology known as “ant following” is where birds such as Tanagers, Woodcreepers, Anis, etc., and even other insects such as butterflies, wasps, flies, mites, beetles and lizards, follow army ants to feed on the arthropods and other small vertebrates flushed from the forest floor. But many times, these other smaller creatures become food for the birds as well. Another reason why birds follow army ant swarms is for anting. “Anting”, is a specialized behavior in birds and is the application of ants or ant substitutes to the feathers, and can be divided into two forms; active and passive anting.
During active anting, birds seize several ants in their beaks, crush them, rub them, and place them among their feathers. During passive anting, birds lay down among the ants and permit the ants to invade their plumage. The birds stretch out one or both wings, spread their tail or tuck it forward between their legs. Suggested reasons why birds have adapted to anting is for; self-treatment against ectoparasites, treatment of fungal or skin infections, reducing skin irritation during molting, and feeding.
Army ants eject formic acid or other fluids from poison glands which might help to kill or remove mites, lice, and other fungal or bacterial microparasites. Also, birds may apply ants to the feathers to remove the acid before the ants are consumed.
One morning at BFREE, a huge army ant swarm which lasted for a couple hours, swarmed through the compound and followed by different birds. Groove-billed Anis, Grey-headed Tanagers, Northern-barred and Tawny-winged Woodcreepers, Clay-colored Thrush, a Great Kiskadee and a Hooded Warbler, followed the army ants feasting on insects being stirred as the ants swarmed on the compound. A pair of Yellow-faced Grassquits and 6 individual Ruddy Ground-Doves, were also close by foraging but they could have been foraging on other food particles. A scorpion and a Striped Basilisk were also among the army ant swarm possibly feeding on insects as well.
So the next time you come upon an army ant swarm, pay close attention to the ants and the birds flocking them. You may witness a feeding frenzy or “anting” behavior. It also provides a wonderful opportunity to observe different birds from a close distance.
Sources:
Martínez, A. E., H. S. Pollock, P. F. Rodrigues, and J. M. Touchton. 2021. Army-Ant Following in Neotropical Birds: A Review and Prospectus. Ornithology 138:ukaa 078.
Willis, O. E., and Y. Oniki. 1978. Ann. Rev. Ecol. Syst. 9: 243 – 63.
