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Column: Bird anting befuddles scientists

Published 10:45am Thursday, July 9, 2009

While looking up information for last week’s column on grackles I found they were one of the more avid anting birds.

Anting is when a bird in some fashion introduces ants to its feathers. Some do it actively by picking ants up in their beak and rubbing them against their feathers. Others prefer the passive method, stirring up an ant nest and then simply laying down on the nest with wings splayed letting the ants crawl all over it. I’ve long been curious about this. Not all bird species engage in anting but it’s a regular activity amongst those that do.

Over 50 species here in North America are known to indulge, including many perching birds, turkeys, grouse, pheasants and even owls. It seems that in this day and age science can pretty quickly figure out most anything it puts its mind to. However, one that stubbornly eludes us is why birds do it. This behavior was first officially documented in 1935 and has been actively studied ever since but nobody has been able to pin down the reason.

There are just about as many explanations for anting as there are studies done on it. Some scientists try to keep it simple, saying the birds are just removing the foul tasting acids found in most ants prior to eating them. That really doesn’t wash, though, as it doesn’t explain why birds lie on active ant hills. One commonality found by most of the studies is that not just any ant will do.

The ant species nearly all birds choose are those that produce formic acid. Most ants have butyric acid but only a few species produce the odiferous formic acid, which they eject in a spray for self defense like skunks. These are the ones birds strongly prefer for anting. Formic acid producing species rarely, if ever, bite. Is it because they don’t bite back or is there something about the formic acid itself? The most common theory is that the formic acid acts as an insecticide, fungicide or bactericide or a combination of all. Some think the acid may have a medicinal effect on the skin. Others theorize it may be a source of vitamin D enhanced by exposure to the sun which the bird ingests while preening. Another oft heard explanation is that the acid helps keep the feathers from drying out.

To complicate matters, even though called anting, many birds use other things besides ants. Over 40 substitutes have been documented. These include certain other insects, various fruits, hot cigarette butts and matches, mustard, vinegar, hair tonic and even motor oil. Is there some link between all these things that we’re missing or do the birds resort to them out of frustration if they can’t find the right ants?

Often birds get really goofy while anting. They quiver and shake their heads, go into weird contortions and even stumble, fall down and roll over. This may imply anting provides some form of stimulant. Perhaps the formic acid provides an intoxicating, pleasurable effect like cats with catnip. It’s also been suggested that the ant movement is like getting a massage but that doesn’t explain the birds that crush the ants and rub them on their feathers.

Why kill your masseuse? One researcher using a captive oriole concluded it had something to do with the burning sensation caused by the formic acid. He tested the ant species the oriole selected by touching them on his tongue and noticed all the ones chosen left a mild burning sensation on his tongue. When he killed the ants by heating or freezing, the acid no longer produced this sensation and the oriole rejected them. Those killed by other means still caused the hot feeling and the oriole readily preened with them.

But the oriole didn’t apply the ants all over itself. It did almost all the ant rubbing under its tail, particularly around the vent. This led him to theorize the heat sensation from the acid was a sexual stimulant. Did he have a kinky oriole or could the formic acid be the new wonder drug for hemorrhoids? Carpe diem.

Larry Lyons writes a weekly outdoor column for Leader Publications. He can be reached at larrylyons@verizon.net

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