You never know what to expect when you’re out looking for new bird species on a bird watching trip. One of our group spied a Great Tit — ah, we had seen that one before, and in fact they are rather common, especially where there are bird feeders.
But then this bird started to do something very uncommon (to us). It dropped to our feet about 10 feet away and began rubbing its ventral surface on the ground, stopping every now and then to pick up something from the ground and tuck it under its wing.
This is most likely “anting” behavior, in which birds rub themselves on anthills or place ants individually on their bodies, as this Great Tit is doing. Over 200 species of birds have been observed “anting”, especially when they are molting new feathers or have an especially heavy load of feather mites or other parasites.
The ants carry a load of formic acid as a defense, and will release it when poked or pinched — which the birds do when they pick them up, or rub against them on the dirt of their anthills. The formic acid, in turn, acts as a deterrent to the bird’s parasites, because it is a natural miticide. So, the bird uses ants as a chemical defense against other arthropod parasites.
But that’s not the end of the story. The ants having released their toxic chemical are now fair game to be eaten, and provide some nutrition if a bird eats enough of them. So, as the bird preens its feathers after its ant dust bath, it can safely consume any stray ants it comes across — sort of like a dessert menu item. And this was quite nicely proven in an experiment by two Cornell biologists (in 2009) who observed that Blue Jays ate 90% of the ants that had been relieved of their formic acid, but engaged in anting behavior instead with ants that were intact (containing their sacs of formic acid).
Two benefits for the price of one interaction, to solve the problem of the big itch.
*The Big Itch is a play on words, based on the record set by our guides Alan Davies and Ruth Miller for bird species seen in a year (more than 4300) and described in their book — “The Biggest Twitch — Around the World in 4000 birds“.