Smithsonian's National Zoo Mourns Loss of Female Gibbon

The National Zoo’s 27-year-old female Northern white-cheeked gibbon (Nomascus leucogenys), Siam, died this morning after an aggressive encounter with Mickey, a 25-year-old male gibbon. Keepers separated the pair and immediately brought the injured female to the veterinary hospital, where Zoo veterinarians attempted to stabilize her despite several severe injuries. A final pathology report will be completed in three weeks.

“The primate staff is very saddened by the sudden loss of Siam who has been under our care for the past 23 years,” said Lisa Stevens, curator of Pandas and Primates. “We are especially shocked that it came as a result of aggression from her cage mate in such a swift and unpredictable act. Siam was an excellent mother and companion to her long-term mate Ralph, who was euthanized this past June due to severe illness. Their offspring will contribute to the future success of the Species Survival Plan.”

Accredited zoos participate in animal breeding programs called the Species Survival Plan. The SSP scientists determine which animals breed by considering their genetic makeup, nutritional and social needs, temperament and overall health. Siam and Mickey were paired together based on an SSP recommendation. Social animals, gibbons live in small, monogamous families composed of a mated pair and up to four offspring.

Siam made significant contributions to the survival of her species; while at the National Zoo, she mothered four offspring. Sydney, a male born to Siam in 1999, remains on exhibit at the Zoo.Between five and seven years of age, white-cheeked gibbons become sexually mature, and while males’ hair remains black, females’ hair turns a golden-beige color, similar to that of infant gibbons. Siam, however, lost her gold color and turned black as a result of an ovario-hysterectomy. This color differentiation made her easily distinguishable from the Zoo’s remaining female white-cheeked gibbons, Mae and Muneca.

White-cheeked gibbons are listed as critically endangered on the International Union for Conservation of Nature’s Red List of Threatened Species. Populations have declined by more than 80 percent over the past 45 years due to habitat loss and trapping for the pet trade. The lifespan of a wild white-cheeked gibbon is usually about 25 years; for a gibbon in human care, that number can be 40 years or higher.

Native to Viet Nam, Lao People’s Democratic Republic and China, these lesser apes are one of the few apes where the adult female is the dominant animal in the group.