I was watching this solo Black Oystercatcher on a rock off the east side of the seasonal Burrowing Owl sanctuary. Its vivid beak and eye colors seduced me once again into clicking the shutter, see photo right. But this is not a post about the bird’s eye. Next, my lens traveled downward. I confess I have a thing for birds’ feet. They’re so interesting, so diverse, so well adapted to their habitat and lifestyle. There I saw something that surprised me. The bird had ants on its foot. Pretty big ones. Not only on its foot, but on its whole leg, on its ankle joint, and above, going into its belly feathers. What the heck?
The bird was standing on a rock in the intertidal zone; at high tide it would be flooded. Not very likely that the ants lived on the rock and climbed aboard the bird when it landed there. The bird is a shorebird quite capable of wading in water up to its belly; it could have easily washed the ants off if it wanted to. And, obviously, the bird has a formidable beak, well adapted to picking off any bugs that bothered it. But the bird paid no attention to the hitchhikers crawling up its leg and into its feathers. Maybe the bird has no nerves on the skin of its leg and didn’t know the ants were there. Birds have no nerves in their feathers so the ants could be running riot in there and as long as they didn’t bite the bird’s skin they’d be fine. Puzzled, I googled “birds, ants” — and got immediate hits.
It seems that more than 200 species of birds have a relationship with ants, so much so that there’s a verb for it, “anting,” and a Wikipedia page. Some birds spread their wings and flap their tail on an anthill, annoying the ants and provoking them to crawl all over the bird’s plumage. Other birds grab ants in their bills, crush them a little, and rub them on their feathers. In some bird species that were tested, this behavior was built into their DNA. Theories vary why they do it.
(A) Ant insecticide. Ants can exude formic acid, a chemical they use to make themselves taste bad. It repels insects. Birds deliberately annoy the ants and get them to spray their insecticide to kill the tiny bugs that infest birds’ feathers and skin. Or the bird squeezes the ant to exude the acid and then rubs the moist ant over its feathers.
(B) Dinner prep. In this theory, the birds get the ants to jettison their formic acid so that they’ll taste good when the birds eat them. Lots of birds eat ants, why not?
(C) It feels good. In this theory, the birds don’t get insecticidal help nor nutritional benefit, they just love to do it because they’re hooked on it, like smoking a cigarette or chewing gum.
OK, theory A is the most widely credited, but proving that the ants are actually killing or driving off the parasites that bother the birds, and this is why the birds do anting, hasn’t been easy.
Well, none of those behaviors exactly fit what I saw with the Oystercatcher. The bird wasn’t squishing the ants and rubbing itself with them. It wasn’t sitting on a heap of them and taking an ant bath. It wasn’t eating them. It was letting a small number of ants roam freely on its body. Were the ants feeding on parasites that bothered the bird? Were they relieving the bird of the need to preen, or part of it? Or was the bird just oblivious — ants, what ants? It’s another case for my MATWOB file (Mysterious Are The Ways Of Birds).