Somali Lesser Galago, Galago gallarum
SOMALI LESSER GALAGO
Geographic Distribution and Habitat
The Somali lesser galago, or Somali bushbaby, is the only primate in Africa that occurs in the driest and thorniest of habitats in the semi-arid thorn scrub and woodlands of central and eastern Kenya, in southern Somalia, and in the far south and central east of Ethiopia. They can be found in the Webi Shebeli River Valley in Somalia, Meru National Park, Tana River, and Lake Turkana in Kenya, the Rift Valley in Ethiopia, Moyale on the Kenya-Ethiopia border, and even in oases filled with acacia and doum palm in the southeast Chalbi Desert. They occur from sea level to 4,101 ft (1,250 m) and they are capable of surviving in severely degraded habitats.
In Kenya, the Somali lesser galago is sympatric with the northern lesser galago (Galago senegalensis), but generally within its range, the Somali lesser galago is the only primate present.
According to the most recent data, there are 14 species within the genus Galago, although that number is frequently disputed and revised, particularly because species within the genus can be quite difficult to differentiate from one another. As a result, researchers have to rely on vocalizations, genetics, and morphology instead. Luckily, more detailed studies have resulted in the clarification of the taxonomy within the genus—for instance, the northern lesser galago was regarded as a single species with many subspecies, but they were revealed to be seven distinct species instead, which is how the Somali lesser galago received its status as a distinctive species with its own vocalizations, behaviors, and habitat requirements.
Size, Weight, and Lifespan
Lesser bushbabies in general are small primates ranging in average mass from 2.5 to 11.1 ounces (70–314 g) and with an average length of 5.1–7.8 inches (12.9–19.9 cm). The Somali lesser galago sits right around the middle of the pack at 7.05 ounces (200 g). All lesser bushbabies have tails that are longer than their bodies, usually 3.5–8 inches (9–20.5 cm) long.
On average, their lifespan is 16 years.
In general, lesser bushbabies are small, woolly, long-tailed primates with large, thin ears. Many species are indistinguishable from each other, but luckily the Somali lesser galago does not have such a problem—it can be one of the easiest bushbabies to distinguish. The dark brown-gray fur that lines their eyes is unique against the light white fur of their face. Their ventral fur is much lighter than the rest of the body, which is a darker brown-gray. At night, a spot light can help emphasize the dark eye rings, large dark ears, and tail as they contrast against the pale face of the Somali lesser galago. The northern lesser galago, which the Somali lesser galago is sympatric with, can be distinguished because of its lighter, gray-pinkish ears as opposed to the Somali lesser galago’s dark ears.
Somali lesser galagos have extremely large, round, orange eyes (helpful for their nocturnal lifestyle) and a small, pointed nose. Their fingers are large for grasping and clinging and their fur is thick and woolly.
Somali lesser galagos feed primarily on fruit, insects, and gum (the latter most especially during the dry season). During such time, they cling to the rough bark of acacia trees and then consume the gum leaking out of insect holes. These primates consume two types of gum: one is yellow and high in sugar and the other is dark brown. Both consist of carbohydrates and water and provide a good source of fiber, protein, calcium, magnesium, and potassium. In the event that gums have hardened, Somali lesser galagos will use their tooth-comb to scrape it off and the bacteria in their stomach helps break it down. A tooth-comb is a dental structure in the lower front jaw of some animals that are grouped as if to form a comb that is used by these animals to groom and clean their fur or hair.
Somali lesser galagos have developed a moisture-saving nocturnal lifestyle by sourcing their water needs from the food they consume, which is a different approach from other primates species like vervet monkeys (Chlorocebus pygerythrus) and yellow baboons (Papio cynocephalus) that occupy the same habitat in parts of its range and need to find fresh water to drink every day or so.
Behavior and Lifestyle
The Somali lesser galago remains one of Africa’s least known primates; due to the arid, species-poor habitats where they live, they are expected to possess a number of unique behavioral, ecological, and physiological adaptations.
Like all lesser bushbabies, Somali lesser galagos are nocturnal (active at night) and arboreal (tree-dwelling) and they tend to inhabit all strata within their habitat with a range of 3.3–23 feet (1–7 m) above the ground. These little primates move through their environment by quadrupedal (on all fours) movement, leaping, climbing, and hopping. They move very quickly through even the thorniest vegetation and make leaps of up to 8.2 feet (2.5 m) between branches. Somali lesser galagos are vertical clingers and they climb head-first down trees. On the ground, they hop on their hind legs between bushes and trees.
Among primates, Somali lesser galagos rely the least on vision; they have large eyes with a limited range of eye movements, which means that they have to utilize more movements with their entire head to explore their environment. Even with their agile leaping, they use less hand-eye coordination and more olfactory and auditory stimuli, which is assisted by their large ears.
Galagos are called bushbabies because some of their calls sound like crying human babies.
Somali lesser galagos are either solitary or live in small groups of two to three individuals. These nocturnal primates spend the majority of their time foraging for food, followed by traveling, social activity, resting, and other activities. Their active time starts right around sunset and ends around dawn, when they regroup at sleeping sites at day break. However, when temperatures are cooler, galagos shorten their foraging activities by several hours and return to their sleeping sites early. Unlike other lesser bushbabies, Somali lesser galagos do not make nests or enter holes to sleep, but instead retreat into dense clumps of thorns that provide safety from predators during the day time. Occasionally, they will occupy an abandoned nest.
Male Somali lesser galagos tend to spend the majority of their time completely alone, even more so than the females because they also sleep alone. Mothers will stay close to their offspring and other females, especially while sleeping, and they will travel with their own offspring up to 1.2 miles (2 km) to forage. There is no record of females having confrontations, but males have engaged in violence, though it is quite rare and usually the result of a vagabond male moving through another male’s territory.
Of lesser bushbabies, the Somali lesser galago is generally less shy and in one study actually moved towards the spot lamp utilized by researchers to a distance of 3.2–16.4 ft (1–5 m).
All lesser bushbabies have unique vocalizations called advertisements that actually help distinguish species that are otherwise nearly impossible to tell apart. Advertisement calls are usually heard upon emergence from the sleeping sites, when they reconvene at dawn, and for maintaining contact.
The Somali lesser galago’s advertisement call, a “quack,” is most frequently used within an hour after dusk and during the hour prior to dawn. This “quack” is audible to the human ear as far as 984 ft (300 m) away.
Somali lesser galagos also have a couple other vocalizations, including:
- Rolling call—buzzing single notes repeated slowly or strung together in a sequence; used for group cohesion
- Squawk yaps—harsh yap-like barking notes repeated rapidly in long sequences; alarm call
The mating system of all lesser bushbabies is best described as dispersed and not strictly polygynous, the latter being a mating system in which one male mates and lives with multiple females. Gestation periods can range from 111 to 142 days, with smaller species having shorter lengths. Sexual maturity is reached between 8 and 18 months of age. Mothers can give birth to up to 4 infants per year and usually only to one infant at a time (although twins are possible). In both the wild and captivity, females may mate with more than one male during a single estrus. For the Somali lesser galago in particular, all matings are initiated by very persistent males, with females being generally averse to their attempts.
At birth, infants have open eyes and gray coats. By two to three weeks, their thick fur comes in and they begin more independent movement and exploration. At one month, infants begin to consume solid foods, even by way of stealing from the mouths of their mothers. Mothers will park their infants in nearby trees or thorns while they forage, but instead of carrying their infants in their mouths like other lesser bushbaby species, Somali lesser galago mothers carry their infants on their bellies, with the infants clinging to the fur instinctively.
At about 10 weeks of age, infants are weaned. From that point forward, the offspring initiate most of the contact with the mother, often by unreciprocated grooming. Males are not involved in the rearing of their young in any capacity.
No specific information is known about the ecological role of Somali lesser galagos, but it is likely that they act as seed dispersers within their habitat.
Somali lesser galagos are listed by the International Union for Conservation of Nature’s Red List of Threatened Species as Least Concern (IUCN, 2016). They have a stable population trend, though a number of subpopulations throughout the range may be threatened by habitat degradation, fragmentation, and loss. Somali lesser galagos are patchily distributed and locally common, and they are understandably absent from large areas of unsuitable habitat throughout their range, but have a higher density at some more suitable sites, like Meru National Park. However, lesser bushbabies in general are considered adaptable and able to cope with habitat degradation, and Somali lesser galagos are no exception. It also helps that the semi-arid habitat that Somali lesser galagos occupy is of little value for crop production.
Some potential predators of Somali lesser galagos include mongooses, genets, jackals, domestic dogs and cats, raptors, and snakes.
Somali lesser galagos are listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). In Kenya, they occupy protected areas such as Meru National Park, Shaba National Reserve, Arawale National Reserve, and Dodori National Reserve. Further studies on biogeography, taxonomy, and ecology of this species are needed.
Written by Rachel Heim, March 2021