Annual rhythm and hormonal control of predatory behavior in female ferrets.

The predatory behavior of female ferrets shows seasonal fluctuations which appear to be affected by estradiol. Under natural lighting conditions in the laboratory the annual rhythm of the behavior was observed during anestrus, estrus, pregnancy, pseudopregnancy and lactating period. Females in heat failed to show predatory behavior whereas females in anestrus killed their prey. Exposure of anestrous ferrets to a prolonged illumination (LD 16:8) during winter induced an estrus which inhibited predatory behavior. When estrus was terminated with human chorionic gonadotropin (HCG), predatory behavior did not further regress as it did in control runs. Thus, during the period of estrus, when estrogen levels are presumably high, predatory behavior was inhibited. To prove a possible interdependency of estrogen and predatory behavior, estradiol-17 beta-valerat was chronically administered. This treatment induced the estrous cycle one day after the first injection. Inhibition of predatory behavior occurred following a delay of 28 days. Thus, fluctuations of estradiol levels are a factor which may affect fluctuations of predatory behavior in female ferrets.