Have you ever seen a bird rolling around on the ground as if it were having a spasm? Chances are the bird is either dusting, anting, or sunning, all in the interest of keeping its feathers and body healthy. Care of feathers is a top priority for all birds, because dependable fight is a matter of survival. The most common way to keep feathers in good shape is to bathe in water and then preen, or comb out the feathers to keep them healthy. Another is to bathe in dust, by fluttering and rolling around in dry soil. House sparrows are well known dusters. A dust bath not only helps shape the feathers, but it also may help rid the body of parasites.
Perhaps, one of the most effective, and certainly most bizarre, ways birds may rid themselves of parasites is to roll on ant hills, or on the ants themselves. It is believed that the formic acid that ants produce is a kind of pesticide for birds.
Sunbathing is still another way for birds to cleanse their feathers of parasites. Like anting, the behavior of a bird sunning is so strange that people often think the bird is sick. The hot sun often causes the bird to drop to its belly, spread or droop its wings, fan is tail feathers, and lean to one side. Then it may stare at the sun and gasp for breath as if it were about to die. Like going to a health club, it takes a lot of work to maintain a sound body.
-- George H. Harrison