Geographic Distribution and Habitat
The hamadryas baboon is an Old World monkey found in northeast Africa, predominantly in Ethiopia, Eritrea, Djibouti, and parts of Sudan and Somalia. It can be found in Ethiopia’s Yangudi Rassa National Park and in Eritrea’s Harar Wildlife Sanctuary. There are also populations in Saudi Arabia and Yemen, where they are believed to have been introduced by humans during the era of ancient Egypt. Though it was considered a “sacred baboon” in ancient Egypt, the hamadryas baboon is now regionally extinct in the country.
The habitat of the hamadryas baboon is varied: they can be found in the mountains of Ethiopia, on hillsides, and in subdesert and arid habitats. Unlike many primates, hamadryas baboons live in cliffs instead of trees. The highest priority for this species is finding a habitat with ready access to water.
Size, Weight, and Lifespan
The hamadryas baboon is sexually dimorphic, accounting for a great variance in size between males and females. Male hamadryas baboons can weigh from 44-66 lb (20-30 kg), while females weigh considerably less, typically from 22-33 lb (10-15 kg). When sitting, a male hamadryas baboon is anywhere from 1.6-2.1 ft (49-64 cm) tall; a female ranges from 1.6-1.8 ft (49-54 cm) tall. The hamadryas baboon typically lives around 20 years in the wild, but in captivity they have lived to be older than 30. The oldest hamadryas baboon on record lived to be 37.5 years old, in captivity.
There is a notable difference in coloration between male and female hamadryas baboons, making them sexually dichromatic. Females have brown fur with hairless faces and hindquarters of a similar color. Males are more colorful than females, with striking silvery fur that grows in a prominent mane around their heads and on their shoulders, emphasizing their pink faces. They have strong brows over their deep, expressive eyes, and long, narrow snouts with short hairs around their mouths—which are home to large teeth. Their bottoms are hairless and pink, like their faces.
Males look similar to females until they reach sexual maturity. Females’ backsides swell up when they are in estrous, and become a striking red when pregnant. Both sexes have tails anywhere from 1-2 ft (31-61 cm) in length, tipped with tufts reminiscent of the end of a paintbrush. Being baboons, these monkeys have prominent ischial callosities, or sitting pads, which allow them to sit for long periods of time, including while they sleep.
What Does It Mean?
Not occurring during or limited to a particular season: not seasonal.
When male and female animals of the same species display different colorations.
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Hamadryas baboons are omnivores, but the majority of their diet consists of plants. Since they often live in dry regions, they are able to get by on a poor diet for long stretches of time when they have to. Populations in Africa rely heavily on acacia trees for their roots, seeds, leaves, flowers, and pods; populations in Arabia are known to eat cactus fruit and palm nuts. The species also depends on desert dates, the fruit of the Balanites aegyptiaca tree, and has been known to hunt small mammals.
Behavior and Lifestyle
The hamadryas baboon is a diurnal primate, which means they are active in the daytime. They spend their days foraging for food, and then retire to the cliffside to rest. They are quadrupedal and will travel anywhere from 4-12 mi (6.5-19.6 km) daily. Hamadryas baboons play together and spend time grooming the male leader of their group.
Daily Life and Group Dynamics
Hamadryas baboons operate in a one male unit (OMU), in which one polygynous adult male mates with multiple females, each of which bears one offspring. An OMU can be as small as two baboons—one male and one female—or as large as 23. There is often an additional male, believed to be related to the leader of the OMU, who serves as a “follower.” It is a strict patriarchy, and the male leader is very protective and possessive of the female members of his group, called a “harem.”
The social structure has many levels. At the smallest level, there is the the OMU, which does everything together—eating, foraging, and traveling. The OMU is part of a larger “clan” of OMUs, of which the dominant males are believed to be related. Clans group together to form a “band” of several hundred baboons, which will reunite throughout the day and share a sleeping site on the cliffs, seeking protection from predators.
Various social cues provide a means of communication for the hamadryas baboon. Yawns, prolonged stares, and head-bobs are all ways to threaten another baboon. Male baboons protect the female members of the OMUs from other males, and will bite the females’ necks to keep them from venturing off. Males will also bark at each other to defend their harems, and also bark at predators.
Reproduction and Family
The hamadryas baboon breeds aseasonally, and females are in estrous from 31-35 days. The leader of the OMU has exclusive mating rights to the females. The gestation period is between 170 and 173 days and the mother typically gives birth to only one infant. She only gives birth once every 15 to 24 months.
The infants are cared for primarily by their mothers, who nurses them for up to 15 months; the males will play with their young and protect their young from threats. Predators are a concern, and so are other baboons who sometimes kidnap infants. As is typical of baboons, offspring are given a great deal of attention.
The hamadryas baboon is often called the sacred baboon because it was considered sacred by Thoth, the ancient Egyptian god who balanced good and evil and also served as the scribe of the gods. Thoth himself would sometimes take on the form of a hamadryas baboon. Some hamadryas baboons were even mummified.
In pursuit of food, the hamadryas baboon digs, helping to aerate soil. Like many primates, the hamadryas baboon also plays a role in seed dispersal.
Conservation Status and Threats
The hamadryas baboon is a species of Least Concern, according to the International Union for Conservation of Nature (IUCN, 2016); however, they are often killed in pest control efforts, since they sometimes live close to humans and have been known to eat farmers’ crops. These baboons are also used for medical research, and sometimes hunted for their hides. As human agriculture expands to a larger scale, this puts the hamadryas baboon at increased risk—both due to habitat loss and increased potential for conflict with humans. They are also susceptible to predators such as leopards, cheetahs, hyenas, and eagles, which is why they travel in large groups.
Because the hamadryas baboon is found both in Africa and Arabia, some researchers believe there is genetic variation between the two populations, and that precautions should be taken to protect the population on the Arabian peninsula, where the monkeys come into more frequent contact with humans.
Written by James Freitas, April 2018