Copulation patterns are important to understanding male mating strategies and stabilization strategies of
social organizations in primates. However, information on copulation patterns of Asian primates is relatively rare. This
study was undertaken to collect data on mating behavior and birth seasonality of Black-and-white Snub-nosed monkeys
(
Rhinopithecus bieti
) using all occurrence sampling and Focal animal-scan sampling methods at Mt. Lasha, between
January and December, 2011. Our study focused on observing mating frequency and birth rates. Snub-nosed monkeys
mate year round, with two observable peaks: one reproductive peak during the mating season, roughly from August to
October, and a second non-breeding peak during the birth season. It is unclear what biological significance this
non-reproductive mating peak has. During our observation, we noted a lower ratio of mount to ejaculation and rare
ejaculatory copulations, which indicated that every mating would not result in ejaculation. This study corroborates the
previous view that the
Rhinopithecus bieti’s copulatory pattern is likely multiple-mount ejaculation (MME) or at the
upper part of mating continuum of single-mount ejaculation (SME) toward MME. More ejaculatory copulations initiated
by males than females indicate that MME is not only a mating strategy of males, but that males can influence the position
of their copulatory pattern on the continuum between SME and MME. The mating frequencies significantly correlated with the birth rates with a delay of 6 to 7 months. Monkeys gave birth within a strict seasonality with a birth peak of
March, which confirms the previous view. Infants were born with a certain degree of synchronization, but different
populations displayed different modes of synchronizations.
