Oh, yes they do! Last winter I was on "thaw patrol" every ten hours or so,
as the nectar would freeze solid and need replacing. Here's a link to a pic
of one of my little guys from last year--even our snowfall didn't dissuade
this brave hummer!

http://farm1.static.flickr.com/131/354199948_04be2b2f18_o.jpg

**Happy birding, and keep those hummies fat!

Susan Littlefield