Mother rabbits and their offspring: timing is everything

Mother rabbits nurse once every 24 hr for ca. 3 min. The contribution of pup stimulation to the regulation of this process was investigated by: reducing litter size to one pup, covering all the mother's nipples, or taping the mouths of an eight-pup litter. Time inside the nest box with the young significantly increased under all these conditions. Yet, eight pups sucking on a single nipple allowed a normal time in the nest box. Bringing the litter to the mother earlier than usual promoted maternal behavior expression twice in 24 hr; the proportion of responsive females and the time at which they responded depended on the size of the litter suckled. These findings indicate that: (a) suckling determines the time inside the nest box and prevents mothers from responding to further pup stimulation for a variable time; (b) pup exposure promotes maternal behavior, even "out of phase" with circadian rhythmicity.