White-tailed ptarmigan name "Tetrao (Lagopus) leucurus" by the Arctic explorer John Richardson in 1831. It was later determined that "Lagopus" had sufficient distinguishing features to be regarded as a separate genus and the bird became "Lagopus leucurus". Molecular studies have shown that "Lagopus" is monophyletic, with the rock ptarmigan ("Lagopus muta") and White-tailed ptarmigan being sister species. The position of the willow ptarmigan ("Lagopus lagopus") is less clear cut, it showing some genetic divergence over its wide range. The genus name "Lagopus" is derived from Ancient Greek "lagos" (λαγως), meaning "hare", + "pous" (πους), "foot", in reference to the bird's feathered legs.
Winter white dwarf hamster able to sense a directional change in photoperiod length, such as in one experiment that demonstrated a transition from 16 hours of light to 14 hours initiates a change to the winter coat. The change to the winter coat can be triggered in the summer by the short day lengths. The change occurs back to the summer coat in the autumn, when the length of the days change again. At internal temperatures hamsters in captivity start later with the changes. The winter colour is less pronounced in them. The eyes of the Winter white hamster are black, unless it is