Copulatory behavior of Syrian golden hamsters in a one-male two-female test situation

Eighteen male hamsters each completed two tests of copulatory behavior: one with one female present and one with two females. Males displayed only relatively small, quantitative alterations of their typical copulatory pattern in the two-female vs. the one-female situation. All males mated with both females. Shifts between females tended to occur at predictable times-particularly after ejaculations and those long intromissions that did not immediately precede ejaculations. When mating in the two-female situation, males sired more offspring than with one female. Females in the two-female situation received less copulatory stimulation than in the one-female situation, but there were no detectable deleterious effects of this reduced stimulation on reproduction. Should copulation occur between one male and two females in the natural habitat, it would appear to be of reproductive advantage to the male, with no detriment to the female.