Abstract: Summary One hundred and forty-four naive virgin female golden hamsters were each given a single 15 min test with three pups aged from day 1 (<24 hr) to day 18. A group of eight females was tested with each age of pup. Pups aged from day 1 to day 6 were generally attacked like prey, killed and eaten. Pups of intermediate age (day 6 to day 10) were usually initially attacked but this was often followed by maternal responses. The females', behaviour with the oldest pups suggested that they were being treated as strnge adult intruders. This result differs from that of a similar experiment with mice in which the youngest pups were found to be the most effective for eliciting materal responses. An explanation for this difference in terms of the evolutionary history of the golden hamster species is proposed.

Abstract: Summary Initial contact with pups of a certain age causes changes in virgin female hamsters' behaviour with pups of another age. This was shown by comparing the behaviour with 5-day-old pups in groups of naive (control) animals and of animals given one previous contact either with 1, 5 or 9-day-old pups. Maternal responses were more intense in the animals previously presented with 1 or 9-day-old pups than in the control animals. Attacking was increased after initial contact with 1-day-old pups and decreased after initial contact with 9-day-old pups. Animals presented twice with the same pattern did not show marked changes in either of the two activities.