Animals have always been able to sense changes in weather and storms. In fact, as a little girl I was somewhat amazed by what appeared to be my grandfather's psychic abilities. He was always able to forecast the weather. He clued me in when I was about 7. He wasn't predicting the future, he was watching his herd. You could tell a storm was coming by their behavior, how serious the animals thought it would be, and which direction it was moving all by watching the animals.
I believe God sent the animals to Noah, and I believe that after the flood God dispersed them, but if that won't satisify a skeptic, remind them that science teaches the continental plates were once connected to one another, and that certain land masses change.
There are also cases of nautral phenonomen in modern times that amaze people. I've seen it rain frogs. We've probably all heard the stories of tornados scooping up farm animals and then depositing them, alive, many miles away.
Animals migrate. They have an uncanny ability to find ways through things that we never dreamed of.