Gombe Stream National Park
Redtail and Blue Monkeys
The redtail is easily recognized by its bright orange-red tail, white nose and cheeks, and its sharp bird-like chirps. It is a smaller relative (3-6 kgs) of vervets and blue monkeys. Throughout its range (covering much of Central Africa) this species inhabits lowland forests, being particularly successful in secondary growth. Redtails eat a wide variety of foods, including the fruits, flowers, shoots and young leaves of many forest trees; also insects, which make up about one-quarter of their diet. Groups consist of a single adult male with several females and their young, about 30 in total, defending a territory of 0.25 sq km. They are exceptionally agile and fast in their movements through the forest canopy, so you may find them hard to watch.
Blue monkeys are larger (5-8 kgs) than redtails and vervets and are dark grey or blue-grey with black limbs. Their most characteristic calls are a very loud, deep, explosive"pya" or "cha-cha-cha-cha" though they also make various chirping sounds. They eat a similar range of foods to redtails, except that they eat more leaves. They are found in all kinds of forest, especially highland forests, and appear to suffer from heat if they do not have access to shade. Like redtails, blues live in territorial, one-male groups, but the group size tends to be smaller (around 20) and territories larger (about 0.6 sq km) than for redtails. They only defend territories against their own species, and frequently associate with redtails.
The single breeding male of a group is replaced by another, on average every 2 years or so, and competition among males for"harems" of females is intense. Sometimes an unsuccessful blue male joins a redtail troop. The redtails slowly accept the alien and the females may eventually mate with him, producing hybrid offspring.
Such hybrids occur at Gombe and show a mixture of both species' characteristics. For example, they usually have the redtail's white nose but the blue monkey's dark tail and large size. In areas where they have been studied in detail, such hybrids have proved to be fertile.
This suggests that blues and redtails, despite their striking physical differences, have only recently diverged as separate species, presumably while geographically isolated from one another. Now that they are again sharing the same habitat, it will be interesting to see if they can maintain their identity as separate species.
The main enemy of redtails and blue monkeys is probably the crowned eagle, and indeed they seem to avoid the top of the tree canopy where they could easily be grabbed. It is remarkable, considering their abundance, how rarely they are caught by chimps; perhaps they are so good at escaping that chimps seldom attempt to hunt them.
Vervets are light grey monkeys with white-fringed black faces. The male has a conspicuous pale-blue scrotum. They are not as vocal as most of Gombe's other monkeys, so you will probably see them before you hear them. Tolerant of heat and open country, they are very common and successful throughout savanna areas of Africa. They are uncommon in Gombe and tend to range through the woodlands of the lower slopes, frequently entering riverine forest to feed. Their food is fruit, seeds, flowers, buds, gum, and insects, and like baboons they readily become bold and effective crop raiders. They live in groups of about 10-20, with roughly equal numbers of each sex, unlike the one- male groups of redtails and blues.
Special Thanks to Thomson Safaris and Tanzania National Parks for contributing Tanzanian information.
Details mentioned in this article were accurate at the time of publication