I wonder why they're OK in such freezing stream...I'm not from snowy region, but I like to walk around snowy and quiet places:)
I think they stay warm with a special kind of feather called "down". Maybe you have heard of it. People often put down feathers in coats and blankets. Here is a link if you want to learn more about it.http://en.wikipedia.org/wiki/Down_featherThey are pretty amazing. I wouldn't last long in that water.