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- Forced copulations by subadult males is used to establish dominance; pregnancy rarely results.
- Cooperative copulations between subadult males and females has also been observed.
- Reproduction occurs mainly through sexual contact between fully adult males and fully adult females.
- Sexual contact is often initiated by the female, who tend to choose the dominant flanged (fully adult) male.
- Males may mate with more than one female (polygyny).
- Orangutan females have a menstrual cycle lasting 22-32 days; a small amount of bleeding lasts a few days
- The menstrual cycle begins at 5-11 years of age; average is 7-8 years.
- Females do not exhibit conspicuous genital swellings during ovulation.
- Age of first reproduction in females, 12- 15 years. In males, 18-20 years.
- Interbirth interval: 7-8 years (Bornean orangutan)
- Interbirth interval: 9.3 years (Sumatran orangutan) (Wich et al. 2004)
- The longest for any great ape population
- In the wild, a female has up to four surviving offspring during her lifetime.
- No evidence of menopause
Gestation & Birth
Gestation: 227-301 days
- Single births most common, occasional twins
- Average birth weight, 1.5 to 2.3 kg (3-5 lbs).
- Sex ratio at birth 1:1
Infant (0-2.5 years)
- Infant mortality is thought to be low.
- Infant spends the first 6-8 months firmly attached to the mother, then begins to spend short periods nearby, but not attached.
Juvenile (2.5 - 7 years)
- 4-5 years of age: independent of mother, but remain in mother's territory
- Up to 7 years of age: Move out of mother's territory
- Weaning takes place as late as 5-8 years of age
Adolescent (7-10 years)
- Females: 20-30 kg (44-66 lbs)
- Independent of mother
- Sexual maturity reached at about 6-8 years of age
- Most social age group.
Subadult Male (10-15 years)
- 30-50 kg (66-110 lbs)
- Sub adult males do not exhibit secondary sexual characteristics typical of adult male
- Development into adult male (accompanied by drastic endocrine changes) may be repressed as long as the individual lives near a fully adult male. Once separated, development of secondary sexual characteristics may occur rapidly.
- Delayed maturation of males may be a social strategy used to allow coexistence of two males
Adult (Female: 8+ years; Males: 15 + years)
- Researchers estimated the age at first reproduction for female Summatran orangutans at 15.4 years (W 2004)
- Development of secondary sexual characteristics in males occurs at 15-20 years of age.
- Adult females and sub adult males difficult to distinguish unless the female is accompanied by young.
- 50-57 years in managed care
- 45-60 years in the wild
- In a study of wild Sumatran orangutans, researchers estimate 58 years for a life span (Wich et al. 2004)
- Potential predators: humans, clouded leopard, tiger, possibly the Asian hunting dog.
- Compared to mortality figures for other great apes, mortality of all age classes is lower in orangutans. (Wich et al. 2004)
- For infants under one year in age, more than three times lowers than chimpanzees and 2.5 times lower than in gorillas
Kaplan and Rogers, (1994)
Leighton, et al., (1995)
Wich et al. (2004)
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