Public Release: 

Orangutans suckle for up to eight years, teeth reveal

Cyclical nursing patterns in wild orangutans

American Association for the Advancement of Science

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IMAGE: Wild orangutan mother and 11-month old infant from Borneo. Investigations of barium in teeth from other individuals show a pattern of increasing mothers' milk consumption during the first year of... view more 

Credit: Tim Laman

Orangutans Suckle for up to Eight Years, Teeth Reveal: Researchers have developed a method for tracking characteristically elusive nursing patterns in primates and used it to discover that some immature orangutans suckle for eight years or more - exceeding the maximum weaning age reported for other non-human primates. The findings could have meaningful implications for managing endangered primates with slow reproductive rates, such as the Sumatran and Bornean orangutans, the life histories of which are poorly understood. Little is known about weaning age in wild orangutans, but some scientists suggest that weaning continues for up to six years (or more) after birth. Barium, a nonessential element, often follows similar pathways in the body as calcium, and is easily incorporated into skeletal tissues such as teeth when maternal milk is ingested. Testing for this element is, therefore, an effective way to indicate if an infant or immature individual is still nursing. In this study, providing one of the first such detailed nursing histories of wild orangutans, Tanya M. Smith and colleagues analyzed barium levels in the teeth of four orangutans starting from their first year of life. They found that after the first year, barium levels generally decreased, but barium was present into the eighth and ninth year of life. Additionally, the authors found cyclical periods of high and low barium concentrations from year to year. They indicate that decreases in barium levels might correspond with times of high fruit availability, when growing animals can be less reliant on milk, while increases in barium are a result of the increased milk consumption that sustains the growing animals during periods of food scarcity. These insights into the nursing and weaning patterns of orangutans are noteworthy, since observing suckling in tree-living, inconspicuous primates is always a challenge.

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