Went through an eclipse a few years back and the flock did return to the coop as if it was nighttime, with some heading to roost, but they reemerged once daylight increased again.
I had to travel a bit for the 2017 eclipse and my chickens of course were not in totality. But tomorrow's eclipse goes right over our house so I'll get a first hand look at what our chickens do. If I can find this thread again, I'll report back!
So, how did they do?
My chickens were caught off guard in the woods when totality hit. They got real quiet and started moving cautiously as a big group towards the coop. When they were almost to the coop totality lifted, and they were left looking about as confused and foolish as chickens can look. It's almost like they didn't trust their senses, because they took a moment to eyeball the area before getting back to their routine.
I also have guineas, geese, and muskovies. They all got quiet and hunkered down where ever they were. The geese and ducks were very still, had their heads tilted and were looking upwards. I think they were watching all the bats emerging from the trees, but I'm tempted to pretend they were joining me in looking at the sudden hole in the sky.
Rojo, our rooster, gathered up his girls and herded them up close to the coop but they did not go in. They just kind of hunkered down close to the run and seemed ... puzzled and a bit stressed. Confused, I guess. I imagined them thinking, How can it be bedtime, we have not had our bedtime snack yet? It was eerily quiet as the day birds stopped singing and calling, then the evening birds started their songs. My son thought it was really cool and impressive. I'm so glad he enjoyed it. We all did!