My chickens have a bad habit of standing in the pouring rain when it's been hot out & then my daughter drags soggy Silkies in the house to be bathed to get the sand & dirt off of them from the run. I have 1 especially who never fails to do this. I think she just isn't smart enuf to get out of the rain...LOL Mine like to dig in damp sand & lay down in it on hot days. They will deliberately dump their water buckets to accomplish this if the sand is not wet enuf for their tastes. However, I have never seen a chicken deliberately take a bath. They tend to get a bit upset & frantic if they accidently end up in the water bucket.