Crowding, reproduction, and maternal behavior in the golden hamster

Hamsters, housed in groups composed of one, two, four, or six females, with two males per group, were observed for a period of 60 days. The effect of such groupings on reproductive success was assessed by determining interference with pregnancy, lactation, maternal behavior, and litter survival. While there was little interference with the onset or course of pregnancy, a marked effect of group size on nursing behavior and litter survival occurred. These effects increased over the course of the experiment so that second litters were less likely to be nursed and to survive in the larger groups. The results appeared to be attributable to a breakdown in maternal behavior as well as to the killing of pups by nonlactating female hamsters. It is significant that the outcome of this experiment, reduced litter survival, parallels the effects that have been reported for other rodents, since different mechanisms are involved in the case of the hamster.