Social and environmental factors influence the suppression of pup-directed aggression and development of paternal behavior in captive meadow voles (Microtus pennsylvanicus).

Rats were tested for induction of maternal behavior by exposing them to young pups continously for 10 to 15 days. Nonpregnant intact, ovariecto-mized. and hypophysectomized females were studied, as well as intact and castrated males. Nearly all the animals exhibited the four main items of maternal behavior and there were only minor differences in the latencies for the onset of maternal behavior among the various groups. It is concluded that all rats have a basic level of maternal responsiveness which is independent of hormonal stimulation.