Reproduction
Males usually reach sexual maturity at about 3-3.5 years old, while females reach it at about two years old. Females approaching estrous can be easily identified because of the swelling and bright red coloration of the genital area. This signals to males that the given female is ready for mating. Moreover, just prior to mating, males will use their fingers to probe the female's birth canal. This is immediately followed by sniffing the area because estrogen and progesterone can be detected by this method, further helping the male conclude if the female is indeed ready to breed.
Gestation is about 6 months for colobus monkeys and one female has about 1-2 new-born every two years. Parental care is intense and often, the role is shared by multiple females of the group. It is observed that about 76% of offspring are born between September and December. Infanticide has also been noted on occasion when a new male joins a given group that has infants.
Research has suggested that the ability for dietary expansion, which consuming charcoal partly allows, explains the higher birth rates and densities due to resource availability. Birth rates for those living in mangroves are higher than colobus monkeys living in coral rag forests.
There are higher birthing rates between October-December for colobines on Uzi Island and then January-February for those in Kiwengwa, located on the eastern side of the main island. Infant mortality can be significantly high with half of the infants born not reaching more than six months of age. The birth rates themselves, however, are actually decreased in comparison to mainland colobus monkeys and interbirth intervals are longer as well. Research has suggested that this is a consequence of disturbed habitats in which mainland colobi are not so affected.
Read more about this topic: Zanzibar Red Colobus
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