Newborn rabbits show behavioral and physiological thermoregulatory responses within the 1st hours of life. Although the mother prepares a nest for her young, she does not stay with them. The hairless immature young survive by huddling together in the nest. In this study, ambient temperature had a powerful influence on the behavior of newborn rabbits and providing they were warm, they did not huddle. The rabbits were studied over the first 10 days of life during which time their fur grows rapidly and their body weight nearly trebles. As each day passed, their preferred environmental temperature fell. In these observations smell and contact with littermates did not appear to have a major effect.