Bioacoustics of Macaca nigra

Breeding. Although Crested Macaques give birth throughout the year, they show an intermediate degree of reproductive seasonality with more than three-quarters of births occurring within seven consecutive months (December—June). In the wild, females usually undergo several ovarian cycles before conceiving. Cycles are relatively long, lasting on average 39-6 days. In captivity, they even extend over this period if males are not available. During ovarian cycles, female Crested Macaques exhibit a pronounced swelling of their anogenital tissue, which is a good indicator of the timing of ovulation. Fully turgescent females are usually mate-guarded by high-ranking males, but they still manage to mate with other males to a minor extent. During mating, females may utter copulation calls, but the frequency and loudness of calls vary between females and between cycles of the same female. Similar to anogenital swellings, female copulation calls, if uttered, also provide a hint to the likelihood of ovulation. Male Crested Macaques may vocalize during copulation, but the function of these calls remains unknown. Similar to most of the other anthropoid primates, females do not show any post-conception mating. Infants are born after a gestation of 175 days, and females give birth only every other year. The interbirth interval is 22 months.

Movements, Home range and Social organization. Crested Macaques live in multmale—multifemale, female philopatric groups, which are, in contrast to other Sulawesi macaques, quite large. Groups comprise 60-80 individuals (adult sex ratio: 1:2-9), but they can grow up to more than 100 individuals. Smaller groups of only 25 individuals have also been observed. Home range size is 74-350 ha depending on group size and time of the year; home ranges are bigger during the rainy season. Home ranges of adjacent groups overlap significantly. Among macaques, Crested Macaques are among those that are the most socially tolerant, with conflicts being of lower intensity, often bidirectional and commonly reconciled. In contrast to more despotic species, female Crested Macaques often exchange affiliative interactions across matrilines. Males, however, fight fiercely over rank and can receive severe injuries. A typical demonstration of male social status is the loud call, which is emitted by all adult group males but significantly more often by high-ranking ones. Male dominance statusis also encoded in the acoustic structures of their loud calls. The red of the male’s scrotum and anus varies in intensity among individuals but also over time in the same individual. It also seems to be a sexual signal, but its precise function still remains unexplained. The extent of the red increases with male age. Males move several times between groups and also have been found roaming the forest solitarily or in small all-male groups. They emigrate from their natal group when reaching adulthood, often immediately trying to take over top dominance in neighboring groups.