Orangutans (Pongo spp.) Fact Sheet: Reproduction & Development

• 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: 227-301 days

Birth

• 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.

Wild populations

• About 40-45 years (Wich et al. 2004; Kuswanda et al. 2021)

Managed care

• Bornean orangutan (Pongo pygmaeus)
  • Median life expectancy (AZA 2023)
    • Males: 27.8 years
    • Females: 37.6 years
• Sumatran orangutan (Pongo abelii)
  • Median life expectancy (AZA 2023)
    • Males: 25.4 years
    • Females: 33.5 years

• 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

Indah and her young, Aisha

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Benirschke, (2002)
Galdikas, (1981)
Galdikas, (1995)
Kaplan and Rogers, (1994)
Leighton, et al., (1995)
Nadler, (1988)
Wich et al. (2004)