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Species Name: Zanzibar Galago (Galago zanzibaricus)
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The Zanzibar galago (Procolobus kirkii) is found in East Africa, mainly in the semi-arid thorn scrub region of southern Somalia, Kenya, and Tanzania, and on the island of Zanzibar. It belongs to the primate family Loridae, commonly known as the “bush babies” due to their unique vocalizations. Both Loridae and the primate’s distribution are endemic to the African continent. The Zanzibar galago has a distinctive appearance compared to the other galagos located on the mainland, with tints of red in its fur and a darker crown, giving it an overall rufus appearance. Unlike the mainland variety, the Zanzibar galago is active during the day, providing a rare treat for visitors to Jozani forest. This places it at an advantage over the nocturnal lemur, with a better opportunity to observe behavior. Activity during the day is known as diurnal, the opposite of nocturnal.
Zanzibar galagos are small, nocturnal primates, weighing around 150 grams (5 ounces) and are approximately 16-18 cms (6-7 inches) in length. They have short, soft fur which varies in colour from light to dark grey, with a long, bushy tail that can be up to 25 cms (10 inches) long. They are distinguished by a characteristic fold of skin on each side of the head. This can be erected when the animal is aroused and serves in communication. Their mode of progression whilst moving on the ground is similar to that of a tiny kangaroo, balancing on the hind limbs and using the tail to provide support. They are particularly agile and are able to make prodigious leaps during which the tail is used as a rudder. They are capable of making vertical leaps of up to 2 metres (over 6 feet). When moving among trees they are much more assured and move predominantly on all fours. Zanzibar galagos have a complex social organisation, living in family groups of six to seven individuals, which consist of a female and her offspring. Adult males live a solitary existence and no male cooperation has been observed.
Behaviour of the Zanzibar galago is similar to that of other galago species in East Africa. They are entirely nocturnal and move through a home range of approximately 4 hectares during the hours of darkness. This is defended by groups from other conspecifics. Home ranges of different groups overlap and group encounters can result in aggressive interactions. The staple diet is made up of insects, fruit and tree gum. Insects are obtained by making small holes in the bark of trees and then allowing the sap to ferment. They will return to these trees over successive nights to obtain the sap at various stages of fermentation. This is an efficient mode of acquiring a high energy food and trees which are utilised in this manner can be an important resource.
The Zanzibar red colobus and Kirk’s red colobus are both considered subspecies of widely distributed mainland species. The Zanzibar red colobus (Procolobus kirkii), found only in the Udzungwa mountains and Zanzibar, is much smaller and darker in color than Kirk’s red colobus (Procolobus tephrosceles), an adaptation to low-level forest vegetation and a large population of red duiker which is its principal predator. Red colobus are highly arboreal and exhibit a number of behavioral and physiological adaptations to this lifestyle. These include highly complex stomach morphology and digestive physiology allowing a diet of mature leaves to be ecologically viable and low basal metabolic rates. Both are adaptations to a diet poor in nutrients and energy. Fossil evidence suggests that red colobus had evolved these traits by the mid-Miocene, and the end result is a highly efficient and low-energy vegetative diet and hence lifestyle. During the Pleistocene, red colobus would have had thick forest cover from the mainland to Zanzibar, but elephant hunting by the Shirazi and subsequent deforestation isolated the colobus populations. Today they are amongst the most threatened of Zanzibar’s primates.
As a group, the mammals of Zanzibar have undergone unique evolutionary pathways as a result of geographic isolation and an island environment. An individual mammal taxon’s evolutionary history is often reflected in its present-day ecology and behavior. We can only speculate on the evolutionary pathways of the various Zanzibar mammal taxa, but they undoubtedly represent a mix of forest-adapted forms derived from an East African mainland ancestry and forms that have evolved island-specific adaptations.
The best place to find Zanzibar galagos is Kiwengwa and Pongwe forests, near the east coast of Zanzibar. These forests have many Zanzibar galagos and it is not difficult to find them at night. It was found that galago density does not vary between areas of forest edge, clearings, shrubland, and tall closed canopy forest, and that the abundance of food plants is the most important factor. However, it is easier to observe the galagos’ behavior in areas where they are using smaller home ranges, and forest edge and clearings are the best places to find them.
The best time to see Zanzibar galagos is at night. During the day, they are more difficult to find as they are sleeping, well hidden in a hole in a tree (possibly an old woodpecker nest) or a large thick vine, and their bodies are covered by the tail. At night, galagos can be found by looking for eye-shine with a flashlight. Galagos are well known for the eyeshine, which is produced by a light being reflected off the tapetum – a thin layer of cells behind the retina that reflects light that has passed through the retina back through the retina, increasing the light available for the photoreceptors in the retina and thereby improving night vision. The appearance of the eye-shine is similar to that of a domestic cat