A Quantitative Description of the Behavior of Rats During Copulation

Abstract

In the normal sequence of events during copulation in laboratory rats, the distinctive ejaculatory thrust of the male is preceded by a series of mounts with and without vaginal intromission, and is followed by a period of copulatory inactivity prior to the next series of mounts and intromissions. In 1922, after a study of the development of the sexual behavior pattern of the rat, C. P. STONE concluded that in the course of the copulatory encounter, both males and females devote the greater part of their time to the performance of activities that have no relation to the sexual act. Indeed, if one combines the data of BEACH & JORDAN (I956) as representative of typical copulatory frequency data with those of PIERCE & NUTTALL (I96I) as representative of typical intromission duration data, one finds that less than one per cent of a typical rat sex behavior test is spent in actual intromission. Yet, there has been little systematic study of the behavior which occurs in the remaining 99 per cent of the test session. Most work has been on the frequencies and temporal spacing of those mounts, intromissions, and ejaculations which constitute such a small, albeit most interesting, part of the total pattern of activity. The most complete study is that of STONE (I922) on the behavior of maturing rats. As STONE was primarily interested in changes in behavior as the rats matured, he had little to say about changes in behavior within test sessions. GRANT & MACKINTOSH (I963) gave a brief qualitative description of some mating postures of the rat. Occasional reference has been made to such patterns as ear-wiggling, back-kicking, and hopping in the female rat (cf. BEACH, I942; I943; 1956), yet without systematic study of the complete behavior pattern. Knowledge of the complete behavior