Groups of 3 males and 4 females were housed in a seminatural environment for a period of 8 days. Female sociosexual behaviours were recorded and analysed from the beginning of behavioural oestrus (defined as the first lordosis response observed in the environment) until the end of oestrus (defined to occur at the moment of a lordosis that was not followed by another one within 60 min). The duration of behavioural oestrus varied between 4.05 and 10.87 h, with a mean of 7.41 ± 0.49 h. In order to analyse changes in behaviour during oestrus, the entire period was divided in 5% segments for each female. The frequency and/or duration of some behaviours changed during the period of oestrus, while others remained stable. Most remarkable among the latter are the frequency of lordosis and the lordosis quotient. From the start of oestrus until the end, the females responded with lordosis to every male mount. Rejections were most frequent at the beginning of the period of oestrus. Then there was a decline, and thereafter rejections remained at a low level, even when the end of oestrus was approached. Paracopulatory behaviours reached a maximum towards the end of the first quarter of the oestrus period. There was no evident decline at the end of oestrus. Females having a high frequency of lordosis showed more paracopulatory behaviours and were pursued more by the males than females with low lordosis frequency. When the behaviour of females with a large number of offspring was compared to that of females with a low number of offspring, no difference in sexual behaviours was found. Comparisons between the females’ behaviour in response to preferred (either defined as the male producing the largest number of lordosis responses or as the male that was most sniffed by the female) and non-preferred males revealed a few minor differences. Location of behaviour was also analysed. Comparisons were made between the environment’s open area and burrow and between different sectors in these parts. Some important differences were found. This is the first detailed description of female rat sociosexual behaviour during the entire period of behavioural oestrus in a seminatural environment.

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.