Chemical contraceptive impacts on cyclic progesterone and sexual behavior in zoo-housed Western lowland gorillas.

For regularly cycling primates in captivity, chemical contraceptives can be used to reduce the likelihood of unintentional offspring, but the effects on cyclic progesterone and sexual behavior have not been well studied in gorillas (Gorilla gorilla gorilla). As zoos are invested in maintaining naturalistic behaviors and physiology, this is an important aspect of gorilla physical and mental health. We examined how exposure to combination and progestin-only oral birth control pills altered cyclic progesterone and timing of sexual behaviors in four female gorillas at four institutions compared to cycling controls. Hormonal data were collected using fecal steroid metabolites as detected by enzyme immunoassay. Behavioral data were collected via one-zero sampling done by keeper staff. All methods of oral contraceptive eliminated the ovarian cycle, with fecal progestogens being maintained below baselines in cycling control individuals. There was also no evidence of any cyclic patterning in endogenous progesterone, suggesting that the methods tested do not allow for detection of a recovery of endogenous progesterone during a short no-pill period. We also found that the oral contraceptives altered the timing of behavioral displays when compared to cycling control individuals but was not directly related to any fluctuations in endogenous progesterone. This study reveals a need for additional research on contraceptive use in gorillas and reinforces that sexual behavior in gorillas is both hormonally and socially mediated.