Female Reproductive Parameters in Wild Geladas (Theropithecus gelada)

Accurate data on reproductive parameters are essential for evaluating the adaptive and mechanistic bases of variation within and between species. Here, we combine fecal ovarian hormone analysis with measurements of sex skin swellings and reproductive behavior to describe female reproduction in geladas living in the Simien Mountains National Park, Ethiopia. We collected 10 years of reproductive data from 197 females across 36 units, with hormone data from a subset of these females (60 females from 16 units). First, we use these data to calculate age at maturation, age at first birth, interbirth interval, menstrual cycle length, gestation length, and duration of postpartum amenorrhea. Second, we present composite profiles of ovarian hormones, i.e., estrogens, progestogens, and sex skin measures across reproductive stages. Third, we examine whether ovarian hormones, sex skin phenotypes, and/or reproductive behaviors reliably reflect fertility or pregnancy in female geladas. The reproductive parameters calculated from our data were similar to those in previous studies on geladas and within the range of those for closely-related baboon species. We were able to reliably identify fertility and pregnancy using fecal estrogens only. The tumescent sex skin phenotypes and reproductive behaviors associated with fertility were also observed across all reproductive stages. We suggest that their presence outside of fertility may be a by-product of the flexibility needed for one or more female counterstrategies to infanticide.