The jay lands on an ant-hill, ruffles up its feathers and flaps its wings and tail. Soon, there are angry ants running all over the jay.
When provoked, ants spray irritating formic acid from their behinds. This is their means of protecting themselves against intruders. Do your own test: Poke about in an ant-hill a little bit, then smell your finger. Formic acid is an effective weapon!
Other birds, for example the starling and the green finch, also practise anting. But what is the advantage of provoking the fury of ants?
It is believed that the purpose is to impregnate the birds' feathers with formic acid. This is in order to kill mites, fleas and lice with which birds are always plagued.