Baboons are large grey-brown monkeys with long faces and tails "hitched up" so as not to drag on the ground. Adult males are larger (in Gombe, 21-35 kgs) than females (9-21 kgs) and have a cape of long hair around the neck and shoulders. They are common throughout Africa south of the Sahara, except for the most densely forested areas. They are very vocal; typical calls are a sharp "Wahu!" alarm or contact bark, various contact grunts given by individuals feeding together, screams and screeches by victims of aggression, and a deep roar-grunt ("Hmm-hmm-hmm-hmm") by adult males.
Tanzania has two distinct races of baboons. Gombe Stream NP has the Olive Baboon, dark, stocky and thick-furred, while in Mahale Mountains NP lives the Yellow Baboon, paler with a shorter coat and more slender build. The dividing line between these two races runs roughly east from Kigoma to Kilimanjaro, then north through Kenya to Lake Turkana, with yellow baboons southeast of that line, and olive baboons northwest.
Baboons are the most successful ground-living primates apart from us, and the most common of Gombe's large mammals. Adaptable and opportunistic, they eat a wide variety of fruits seeds, leaves, roots, flowers, stems, insects, and small animals. At Gombe, more than half their diet is fruit, and they can eat fruit less ripe than that preferred by chimpanzees. They are also more willing to try new foods than chimps are, including human foods, which is why they are considered a pest in many areas.
Baboons can thus use their habitat more efficiently than chimps do, and this enables a fairly large troop of baboons to stay together all the time and to range over a very small area. Sixty baboons can find all they need within 2 sq km, while 60 chimps need an area at least ten times as large to feed them year-round.
At Gombe, several troops have been studied since 1967. Researchers can distinguish individuals by variations in face, build, shape of tail, etc. and have followed the development and relationships of many baboons throughout their lives. Troops consist of about 20-70 individuals with a roughly equal sex ratio. Females form the stable core of the troop; all males emigrate to other troops when mature. Thus the social bonds between the females, who have grown up together and who are closely related, are more stable than those between the males of a troop, who may first have met as adults. In fact, new males seem to join a troop by first making friends with a female, and then fighting for a place in the male hierarchy. Some get killed or injured in the process; thus in most troops, old males are fewer than old females.
The males of a troop compete intensely for status and access to females. A female has an oestrous cycle of 30-35 days, and for about 2 weeks around the time of ovulation she displays a pink sexual swelling. She may mate promiscuously, but at the time of ovulation, she tends to form a consortship with a single mature male, or with several in succession. If she becomes pregnant, she has no further swellings, but her bare bottom becomes a deep, bright pink color. Her baby is born after 6 months, and at first it has pink skin and black hair.
Black infants are the focus of great interest, particularly from females but also from adult males. Occasionally, an adult male will take a black infant (typically from one of his close female friends) and hold it, during a tense encounter with another male. Baboons will not attack familiar black infants, so the male holding the baby may thus prevent other males from attacking him.
At 7 months the infant's coat turns brown, and weaning occurs during the second year. Soon after the infant reaches two, the mother's next baby is born. Juveniles play tirelessly, with each other and sometimes with young chimps, and in beach troops they seem to enjoy playing in shallow water. Both sexes reach puberty at 5-6 years; but females first conceive at 6 years and males reach full size at 7-9 years. Baboons can live for about 25 years.
Intellectually, baboons lack the chimp's problem-solving ability. They use tools very rarely. But they are still clever and swift and should never be underrated.
Watch one of the habituated baboon troops with a guide who knows them. Do not stare directly at baboons, for they may become uneasy and move away or threaten you. Just pretend to be interested in something else. Try to recognize different individuals, and look at the many ways in which males, females and young interact together.
NEVER FEED BABOONS, EITHER DELIBERATELY OR BY ACCIDENT.
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