Groups of rats (3 males and 4 cycling females) were housed in a seminatural environment consisting of a burrow and a large open area for a period of 8 days. Sociosexual interactions were recorded whenever 1 or several females were in behavioral estrus. Male sociosexual behaviors occurred in bouts (periods of sexual activity followed by more than 60 min without any sexual behavior), which could be ended either by mount (mean ± 95% confidence interval was 38 ± 13% of all bouts), intromission (21 ± 15%), or ejaculation (40 ± 18%). Bouts had a median duration of 2.8 ± 0.9 h. Within a bout, the intensity of sexual behavior remained quite stable. Interestingly, there was no decline as the end of the bout approached. There was no relationship between the last event in the preceding bout and the interbout interval. Regardless of whether there was single or multiple females in estrus, the males copulated with all available females in an order that was not significantly different from random. Social behaviors like sniffing and anogenital sniffing were more frequent in the burrow whereas sexual interactions were more frequent in the open area. The seminatural environment employed here offers a considerable amount of information concerning sexual interactions that cannot be obtained in traditional pair tests. Whenever speculations about the biological function or adaptive value of sexual behaviors are to be made, it appears that the present approach is indicated.
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