A Failure to Find Evidence of the Estrus Cycle in the Rat's Activity Level

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maintained on nd lib. food and water. Ss were observed for two weeks every evening from about 7:30 to 1:00 using a time sampling procedure (Bolles, 1960) that yielded 96 observations of each S each evening. All behavior was classified as sleeping, lying, grooming, sniffing, eating, drinking, locomotion, rearing, or manipulating objects. Additionally, the classical estrus signs, lordosis, ear twitching, etc. were watched for, but were never observed. After 14 days observation there appeared to be some indication in some Ss of heightened activity with some cyclicity approximating 5 days, so the general activity phase of the experiment was terminated and direct tests of sexual receptivity were begun. Here S was individually placed in an arena with a pair of males of proven aggressiveness until she could be scored as receptive or not. These tests were run for each S every evening for 5 days and provided quite unambiguous anchoring of the estrus cycle for all Ss. The experimental question here may be put in two ways: (1 ) can the general activity records be analyzed to yield predictions of which day a given S would be receptive, and (2) knowing when S was receptive can some cyclic pattern be discovered in the general activity protocols? The first was attempted prior to seeing the receptivity data; prediction was a little poorer than chance ( 1 out of 16 to the day, and 4 out of 16 to within one day). Evidently, what looked like a 5-day activity cycle in some Ss was just coincidental. Exhaustive analysis of the activity records also failed to indicate any ad hoc correlation between activity in the homecage and sexual receptivity. It seems likely that the estrus cyclicity in activity wheels reported by Wang (1923) and others, of which so much has been made, is a phenomenon specific to activity wheels, and tells us more about wheels than it does about motivation.