I had a batch of chickens escape when I updated to 1.8; that's ok. Some of the chickens got into a wide river, two swam almost all the way across. Since then I've logged out and in again, and teleported away and back too. Now I find the chickens can hardly move in the water. They don't drown, but they move so slightly in any direction that I thought they'd stopped moving altogether. (They turned and their wings flapped, but I couldn't see any other movement.) I tried to lead them with seed. They looked at me, but didn't move towards me. I was able to push them to shore easily, and once out of the water they were able to move well.

Another chicken I have a clearer view of (from a high bridge) seems to move about an eighth of a block in any direction, but then it stops. It bobs up and down very erratically, not bobbing for short periods. The chickens I tried to lead with seed did not bob at all while they were looking at the seed, so I suspect they only dip down when they start to move.

Edit: This slow motion starts the moment a chicken enters the water. (I wasn't clear on that when I initially wrote the report.)