It has recently been found that behaviors elicited in lab are different than in the wild. Rats live in colonies. Almost all females in colony wil come into behavioral estrus at the same time. Females tend to have thier offspring all at the same time. Might promote the survivability of the offspring.
Females also tend to modulate the receptive phase of the cycle differently in the wild than the lab.
During receptive phase, rats engage in lordosis. In a large colony, female will iniate copulation, male will mount and intromit and then the female runs away and then she will allow the male to mount her in 3 or 4 minutes. The timing ensures the vaginal code in which stimulation of the vagina causes the corpus luteum to be maintained and progesterone secreted which will encourage pregnancy. Males may actually secrete phermones that triggers the estrus phase in females and it takes about 3 days to occur. Also insures that all females tend to come into estrus at the same time as found in the wild.