I live in Superior, WI and have had my ferrets for two winters.  I have
noticed that when it gets cold they bulk up.  Even my tiny 1lb girl packed
on the pounds.  Their hair also gets really puffy.  They look like they're
scared, but what's happening is the hairs are getting thicker and moving
apart from each other to create "dead air space" that is easily warmed and
kept warm by the body heat.  It's kinda like when you put plastic over
your windows to create that "dead space" to help insulate the house.
 
When the weather starts to get warmer they'll lose the extra fat and their
hair will smooth out closer to their bodies.
 
Cynthia and Tifa, Padme, Selphie, Jewel, Waffle, & Eggo
[Posted in FML issue 3596]