It’s difficult to capture the cuteness of this chicken behavior with a still camera–we really should try to make a video. Anyway, this is called “dusting” or “dust bathing.” The ladies have dug a hole in our yard and are gleefully rolling around in it, flicking loose dirt under their wings and driving it between their feathers. This is an innate behavior and an important part of chicken hygiene. Dusting suffocates skin parasites that prey on chickens, and it also seems to be pleasurable for the hens, judging by their blissful expressions.
After dusting they puff up and shake off, and settle in to do fine cleaning by preening. When they’re done, they’re all pretty and shiny.
It’s really important that chickens have constant access to dirt–loose, dry, sandy dirt–so they can dust at will. If for whatever reason your chickens don’t have this access, whether that’s because they’re being raised in a concrete floor, or are trapped inside because of bad weather, or your chicken run is swamped with mud, or whatever, it’s a smart thing to provide them with a tray of dirt so they can bathe. Dusting is nature’s favored method of insect control.
ETA: To give you some indication of size, a kitty litter tray would be a good size for a few hens to share, a cement mixing tray for a bigger flock.
Warning: Rant Ahead
We first got our own hens because we disagreed with the industrial style of raising chickens and farming eggs. But at the time that disagreement was purely theoretical–now it’s stronger than ever, because it’s based on practice. The more we know, and experience the fundamentals of chicken life, the more appalling the industrial practices become. One fundamental is that chickens are designed to live on dirt. They love to scratch, peck, dig and bathe in it. Take dirt away from them and you have to scramble to make up for that deficit in unnatural ways. Being unable to scratch, chickens get bored and peck at each other–so their beaks have to be cut off. Deprived of the ability to dust, they get mites and lice, and have to be treated with pesticides. It’s just sad.