Anting is widespread and fascinating, but its purpose is uncertain

10/9/2013 | 0

Blue Jay photographed in Spring Hill, Florida, by S. Hunter Spenceley.

Blue Jay photographed in Spring Hill, Florida, by S. Hunter Spenceley.

A Blue Jay, holding an ant in its bill, spreads and lowers its wings and brings its tail forward between its legs, wiping the outer wing and tail feathers with the ant. The jay has been doing this for several minutes, sometimes losing its balance and stumbling a bit.

The behavior, called anting, is almost comical. It occurs when birds utilize ants in a stereotypic way. It can be active, as in the case of the Blue Jay, or passive, such as when a Wild Turkey or other bird crouches on an anthill with its wings and tail spread, allowing ants to crawl freely throughout its feathers.

Anting appears to be widespread and common but not readily observed. Most information is anecdotal. More than 200 species of birds — mostly songbirds — have been observed to ant. The ants come from two subfamilies, they don’t sting, and they produce defensive secretions to repel attackers. Ants in the first and largest group produce formic acid, which they eject from the tip of their abdomen. In the second subfamily, a repugnant oily liquid is secreted from anal glands.

The function of anting has been debated for years. Proposed explanations have generally related to comfort behavior or feather maintenance. Because anting episodes are most common in late summer and early fall, a period that includes heavy avian molting, some biologists associate anting with the soothing of skin irritated during rapid feather replacement.

A more common belief is that anting controls parasites, such as biting lice and feather mites, which live in the inner catacombs of a bird’s plumage. The concentration of formic acid in the solution emitted by ants is greater than 50 percent, which laboratory studies have shown to be strong enough to kill lice and mites. But whether it will kill mites and lice on wild birds through anting has not been demonstrated.

20 Common birds that ant

Ruffed Grouse
Wild Turkey
Great Horned Owl
Northern Flicker
Cedar Waxwing
Northern Mockingbird
Gray Catbird
Veery
Wood Thrush
American Robin
Golden-crowned Kinglet
Dark-eyed Junco
Song Sparrow
Northern Cardinal
Rose-breasted Grosbeak
Baltimore Oriole
Red-winged Blackbird
House Sparrow
American Crow
Common Raven

Source: Lovie M. Whitaker, A Résumé of Anting, with Particular Reference to a Captive Orchard Oriole. The Wilson Bulletin, September 1957, Vol. 69, No. 3, 195-262.

Birds have used more than ants when anting. They’ve anted with millipedes and bombardier beetles, both of which emit insecticidal chemicals. They’ve anted with marigold flowers, which contain the natural insecticide pyrethrum. Gardeners have been surprised to see birds anting with mothballs added to the edges of their gardens. Mothballs contain the insecticide napthalene. The rinds of lemons and limes contain chemicals to discourage insects from invading the fruit. They, too, have been used for anting. And, although I hate to say it, birds have also been observed anting with cigarette butts.

Yet another function of anting, prey preparation, was suggested decades ago but didn’t gain momentum until more recently. The idea assumes that, during anting, the ants rid themselves of the formic acid in their poison glands, thus permitting the birds to eat them without harm.

Thomas Eisner and Daniel Aneshansley of the Department of Neurobiology and Behavior and Department of Biological and Environmental Engineering at Cornell University wanted to know if formic acid was the reason for anting behavior, so they presented six hand-reared Blue Jays with two types of ants: some that had had their formic acid-containing sac removed and others that were intact (that is, ants that possessed their normal defensive apparatus).

When ants lacking the formic-acid sac were presented to the jays, the birds ate most (96 percent) immediately. When the intact ants were offered, a majority (61 percent) were used for anting. Clearly, the presence of the ants’ formic acid-containing sac was a trigger for anting to occur.

How do birds get rid of the formic acid of wild ants? Both the poison sac and crop are located close together in the ant’s abdomen. Birds that want to eat ants must remove the formic acid but not damage the crop, as it contains up to 30 percent of the total food value of an ant.

Supporters of the prey-preparation hypothesis believe that birds adopted anting as a means of inducing the hapless ants to rid themselves of the poison. By grabbing the ant’s thorax (anterior), a bird does no damage to the poison sac or crop in the abdomen (posterior). When it passes the ant through its feathers during the anting process, the rubbing action induces a defense mechanism in the ant, causing it to eject formic acid. Anting continues until the poison sac is empty. Then the morsel can be swallowed harmlessly.

Two of the six Blue Jays in Eisner and Aneshansley’s study had never been exposed to insects, including ants. Yet their first response to an ant was to initiate anting, demonstrating that they were genetically programmed for anting behavior.

So what is the function of anting? Or is there more than one function for this fascinating behavior? Be on the lookout for anting birds. They are sure to remind you of the complexity of all birds, and to increase your appreciation for how amazing they are.

Read it yourself

Thomas Eisner and Daniel Aneshansley, 2008, “Anting” in Blue Jays: Evidence in Support of a Food-Preparatory FunctionChemoecology 18 (4): 197–203. doi: 10.1007/s00049-008-0406-3. Available on the National Institutes of Health website PubMed Central (PMC).

Eldon Greij’s column “Amazing Birds” appears in every issue of BirdWatching magazine. This article appeared in the October 2013 issue. Eldon is professor emeritus of biology at Hope College, located in Holland, Michigan, and the founding editor of Birder’s World magazine.