Sexual behavior and hormonal estrus cycles in captive aged lowland gorillas (gorilla gorilla)

Abstract

To evaluate whether observed cycles in proceptive behavior in aging lowland gorilla females (age 40+) at Brookfield Zoo were driven by ovarian activity, we compared monthly behavioral data to estradiol and progestogen cycles based on fecal hormone assessments. Progestogen peaks showed regularity and close coincidence with monthly sexual behaviors. Estradiol was more variable. Progestogen peaks varied between 22±5 days for the control female (29 years old), to 24±2.5 and 29±8 for the two aged subjects. In the first aged female, which was housed with other females and a silverback, the high degree of cyclicity in sexual behavior, regularity of progestogen cycles, and close concordance between hormonal cycling and sexual behavior strongly compared to patterns found (in this and other studies) in gorilla females 35 years old, a population that is rapidly increasing in North American zoos as gorillas continue to age. Am. J. Primatol.