BROWN GREATER GALAGO

Otolemur crassicaudatus

Geographic Distribution and Habitat
The brown greater galago, also commonly called the thick-tailed greater galago and the large-eared greater galago, is found throughout southern and Central Africa. The species has populations ranging from Angola in the west, down to the South Africa in the south, as far east as the shores of Mozambique, and as far north as Kenya.

Researchers recognize at least two subspecies of Otolemur crassicaudatus: the Tanganyika large-eared galago, O.c. kirkii, which is mostly found in Mozambique; and the South African large-eared galago, O.c. crassicaudatus, which lives north of O.c. kirkii in Mozambique, Zambia, and Tanzania. Some scientists also recognize a third subspecies: the Miombo silver galago, O.c. monteiri, which exists throughout the main species range.

Brown greater galagos live in tropical forests, subtropical forests, and even savannahs. They prefer to live near rivers and oceans in habitats rich with gum trees.

Brown greater galago range, IUCN 2019

Size, Weight, and Lifespan
Brown greater galagos are the largest of the galagos (also known as the bushbabies). Males are slightly heavier than females, with an average weight of 3.3 lbs (1.5 kg) compared to an average female’s weight of 2.75 lbs (1.25 kg). Both sexes have an average body length of 12.3 in (31.3 cm) and a tail length of 16 in (41 cm).

Galagos can live to be over 18 years old in captivity.

Appearance
Brown greater galagos exhibit great diversity in fur color which ranges from yellow and off-white to darker shades of gray, brown, and black. Their long, bushy tail usually has a black tip. Some males have exposed beige skin on their chests, where their scent glands lie.

The species’ many common names hint at the other defining features of this bushbaby. Called the “thick-tailed greater galago,” they have thick fur covering their tail, which aids balance while crawling across branches. Also called the “large-eared greater galago,” the galago has an average ear length of 2.4 in (6.2 cm), about the same length as their skull. These ears can move independently and can be folded back to communicate threats. Large ears give the galago an acute sense of hearing when hunting insects in the night. As nocturnal animals, brown greater galagos have large eyes, which aid their night vision.

They have thin, long toes and fingers with specialized pads on the ends for gripping onto branches. Although most of their nails are flattened for climbing purposes, galagos have a toilet-claw on the index toe of each hindfoot. They also have a toothcomb, a small set of front lower teeth that are used for grooming and peeling away tree bark to reach the gum.

All galagos are noted for their strong jumping ability, which comes from especially strong calf muscles allowing for jumps far higher than would be expected for an animal that size.

There are slight physical differences between each subspecies:

  • The South African large-eared galago, O.c. crassicaudatus, does not have a black tip on his tail and has darker skin.
  • The Tanganyika large-eared galago, O.c. kirkii is more often yellow or brown and has a longer tail.
  • Miombi silvery galago, O.c. monteiri, is gray and has large ears. Some scientists list the silvery greater galago as an entirely separate species.

What Does It Mean?

Activity Budget:  
A way to quantify animal behavior by observing an animal over an extended period and documenting activity. An activity budget demonstrates how much time an animal spends in various activities such as eating, resting, sleeping, and moving.

Arboreal:
Physically adapted to living primarily or exclusively in trees, such as arboreal-dwelling (tree-dwelling) monkeys.

Nocturnal: 
Active at night.

​Subspecies:
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Toilet claw:
A specialized grooming claw common to prosimians and certain other primates.

Visit the Glossary for more definitions

Diet
The majority of the brown greater galago’s diet consists of tree gum. A galago chooses his habitat based on the number of gum trees available. Gum makes about 62% of their diet, while fruits make up about 21%. The rest of the bushbaby diet contains flowers, nectar, insects, and other small animals.

Diets can vary with location. One study in Kenya found that insects made up over half of the local galago’s diet.

Behavior and Lifestyle
Brown greater galagos are nocturnal and arboreal. They spend the day sleeping high in the trees hidden in a tree hollow or in the vegetation.

Daily Life and Group Dynamics 
A galago walks a similar path every night, foraging for food, marking territory, and watching for intruders. Half the night is spent travelling from tree to tree while only about 20% of the night is spent eating.

Brown greater galagos live alone in a loosely defined territory that overlaps with the territories of other individuals. When two galagos interact, they may form temporary associations in which they sleep together or groom each other. An activity budget found that brown greater galagos spend about 14% of the day interacting with others. Social grooming in galagos is not like grooming in other primates. Galagos prefer to lick the fur of one another rather than use their fingers.

Males tend to have larger territories than females, strategically claiming areas that overlap with as many female territories as possible. Females share their territory with their juvenile offspring who have not yet defined territories of their own. During mating season, both males and females show aggression towards their own sex, but interactions outside of mating season are usually more calm. Brown greater galagos are considered to be friendlier to their own kind compared to other species of bushbaby.

Fun Facts

There are twice as many males as females. Pregnant females compete for the most nutritious sources of tree gum, meaning that it is more advantageous to give birth to males than females who will compete for future resources.

Communication
The name bushbaby references the fact that many galago calls sound like children crying. Researchers have identified 18 distinct calls. Of these calls, one is unique to the brown greater galago: a “buzz” or a “soft-clicking” call made by a baby separated from their mother. Other calls include a variety of barks, whistles, chirps, squeaks, and clicks.

Galagos also communicate through scent. One of the more common behaviors is urine-washing, when an individual washes their feet in urine so that they leave their scent wherever they walk. Some scientists also speculate that this helps the galago grip onto branches. Galagos also rub the scent glands on their chest and genitals on branches in their territory.

Brown greater galagos visually communicate warnings by hanging their mouths open and folding their ears back.

Reproduction and Family
Female brown greater galagos reach maturity after about 495 days (16 months), while males mature after about 639 days (21 months). Males take longer to mature due to bimaturism, or, simply put, males need more time to grow bigger.

Galagos have a set breeding season that changes depending on location. Most galagos mate in August or September, although galagos in Transvaal, South Africa, only mate in November. Some galagos even mate as early as June. Most mating seasons only last a month regardless of location. Mothers give birth after a pregnancy of about 133 days. In a study of 20 captive mother galagos, 60% gave birth to twins, 30% had single infants, and 10% had triplets. Although it is a small sample size, these numbers are in line with wild observations.

Unlike most other primates, brown greater galagos do not carry their offspring as they forage. Instead, they build a nest for their babies where they stay hidden as the mother searches for food at night. Because mothers spend less time with their young compared to other primates, their milk is much richer and carries more nutrients so that young galagos can take better advantage of their limited feeding opportunities.

Fathers do not take on a direct role in raising their offspring, but since they only tend to reproduce with females within their territory, they do indirectly protect their families when they defend their territory from outside threats.

Photo credit: Bernard DUPONT/Creative Commons

Ecological Role
To humans, the most important role of the brown greater galago is insect control. Countries where these galagos are found account for over half of all reported malaria cases worldwide (although one should note that for each reported case of malaria there are 8 that go unreported). Brown greater galagos are one among many species that can keep the mosquito population under control.

Predators of the galago include chimpanzees, snakes, leopards, and birds of prey.

Conservation Status and Threats
The International Union for Conservation of Nature lists the brown greater galago with a Least Concern rating (IUCN, 2018). The population is stable and widespread, the species appears in several protected areas, and they are facing no major threats as a species.

There have been cases of local populations going extinct or close to it, such as a population of O.c monteiri in Lake Victoria that is close to going extinct. Many local populations are threatened by habitat destruction, mostly for agriculture.

Conservation Efforts
The brown greater galago is listed in Apendix II of Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), meaning that although the species is not threatened, trade of the species must be controlled.

The African Wildlife Foundation recommends “conservation tourism” as a means of helping the conservation efforts of bushbabies and other local wildlife. One example is Ol Lentille Lodge in northern Kenya, which employs local citizens and brings money into the region, giving local towns a financial incentive for protecting the environment.

​References:

  • https://alltheworldsprimates.org/Members/Home/MasterPrimate.aspx?tid=870
  • http://www.iucnredlist.org/details/15643/0
  • Groves, Colin P. Primate Taxonomy. Smithsonian Institution Press, 2001.
  • https://www.britannica.com/animal/bush-baby#ref891396
  • https://animaldiversity.org/accounts/Otolemur_crassicaudatus/
  • http://www.theprimata.com/otolemur_crassicaudatus/
  • https://www.theguardian.com/global-development/datablog/2011/apr/25/world-malaria-day-data
  • https://www.awf.org/projects/ol-lentille-lodge
  • Aerts, P. “Vertical Jumping in Galago Senegalensis: The Quest for an Obligate Mechanical Power Amplifier.” Philosophical Transactions of the Royal Society B: Biological Sciences 353.1375 (1998): 1607–1620. PMC.
  • Clark, Anne Barrett. “Sex ratio and local resource competition in a prosimian primate.” Science 201.4351 (1978): 163-165.

Written by Eric Starr, June 2018