I know this comment isn't abaout rain, but I was surprised to see that my chickens like to WADE in puddles. I mean actually walk deeper into them, and stand there. When it was really hot, it made sense, but I have seen them do it recently when it's not warmer than high 60s. (Which to ME is plenty warm, but not to folks - or chickens! - raised in this area!)
I have a hose with a leaky "Y" junction, which I prop up onto the edge of a rubber horse trough so it is constantly refreshed by the water. Might as well use that waste water instead of JUST wasting it. This horse trough tub is the front yard "duck pool" and chicken, cat and dog drinking pool. I don't cap the hose because that junction controls an old-fashioned move-it-around spray sprinkler. On, the sprinkler operates. Off, some water trickles into the black rubber trough. Overflow from it has created a permanent puddle on the low side, and this is what the chickens will step into and stand there, more than ...errr... "ankle" deep.
The chickens (and ducks, too, of course) love to wander through the sprinkler. That's kinda like "fair weather rain."
So I think it's a choice, not a "stupid or not" issue.