Thus spake Pseudo_Intellectual:
What were the crows doing? Wriggling, shimmying through the grass on their bellies with wings unfurled. We know crows engage in play behavior, but this looked like nothing so much as pathetic attempts at recovery after having their wings dislocated by some thuggish onlooker. Still, they hopped up and flew away neatly enough as I approached to investigate the matter. Were these just goofy birds or was there a substance on the ground they were rolling in, a kind of crow-nip? Ants, there are ants on my shoes! Stepping back a bit and shaking my feet I observe that the area of almost highest ant activity correlates almost exactly to the mysteriously favoured spot of the crows.
Some bird species, infected with parasitical lice, will squat or roll around on the ground near an ant nest, to allow ants to crawl into their plumage. Only formic acid-producing formicine ants are used, as apparently formic acid kills bird lice (This is also proposed as the reason why there are no parasitical lice on mammalian species that eat ants, such as the aptly-named ant-eater). Over 200 bird species perform this behavior and while they are not entirely freed of lice afterwards, the lice population on the bird does decrease.
After repetitions of this spectacle (never before observed, then a dozen times in a couple of days), our eventual hypothesis: the crows were intentionally seeking to introduce ants onto their bodies, insinuating them between feathers to eat or otherwise take care of parasites living on the crows. Shit, I knew them crows was smart birds, but if I was a crow I would be spending so much time in the air and trees that I wouldn't ever have even seen an ant, let alone been aware of their theraputic capacities.