[Serial copulatory behavior of male hamsters and rats]

The copulatory behavior of mammalian males is generally characterized by the male's repeated approaches to and mounting of the female. The mounting behavior can lead to intromission, and after several intromissions, an ejaculation occurs. Following ejaculation, the male refrains from sexual activity for a period of time, the so-called "post-ejaculatory interval (PEI)". Most mammals will return to copulate again. Both male hamsters and rats were used and each animal performed five series of copulations with a proestrous female. From the 1st to 5th series of copulations the hamsters showed a shorter PEI than the rats. In addition, the PEI of the hamsters showed no change after each ejaculation, while the rats gradually showed a significantly increased PEI during the five series of copulations.