Good article about the squirrels.  I think the last paragraph is a little misleading in the comparison of squirrels and frogs, though.  Frogs freeze, but squirrels supercool (i.e., don't freeze even when below the freezing point).  Also, some only consider endotherms to be hibernators- ectotherm metabolism slows down as a mere consequence of lower temperatures, while hibernation is a coordinated downregulation of metabolism.