Why: In The Golden Compass, sometimes the Lyra's daemon Pantalaimon turns into one:
Pantalaimon's white ermine fur bristled: she felt it tickling her neck.Answer: Holy moses:
ermine is also goes by the names stoat, ermelin, and short-tailed weasel. Sometimes "ermine" refers to the animal only when it has white fur, while "stoat" only refers to when it has brown fur.
In spite of being such a small animal, the ermine's gestation is among the longest reported for mammals (11 months) because of the adaptation of delayed implantation, or embryonic diapause, in which a fertilized egg is not implanted in the uterus until months later. The animal's "real" gestation is much shorter. This is presumably an adaptation to the highly seasonal environment in which the stoat lives.Source: Google Images
The More You Know: Here is a pretty good explanation about "What are Daemons?"