Colours of Wildlife: Drill

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Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Drill by Willem.

This time I feature a species of monkey that is not at all well-known: the Drill, Mandrillus leucophaeus. It has a much-better-known relative, the Mandrill, Mandrillus sphinx. The mandrill is one of the most spectacular of all primates, and is often represented in art and photography and frequently seen in zoos. Compared to the mandrill, the drill is not quite as spectacular, and yet, it is a very striking and imposing monkey.

Extreme Sexual Differences

The drill, like the mandrill and a few other kinds of monkey, displays a very marked degree of sexual dimorphism – meaning that the males and females look and behave very differently. The male drill is, first of all, much larger: he can exceed 30 kg/66 lbs while the females are up to 15 kg/33 lbs. But his size is exaggerated by a mane of hair over his head, neck, shoulders and chest. Like many baboons and related monkeys, drills have bare buttocks and rumps, which are pinkish in the female but bright red, blue and purple in the male. The male drill also has a bare, red-pink patch of skin on his inner thigh. His genitals are bright red and blue.

The other end of the male drill is not quite as vivid but also visually striking. Unlike the bright blue-and-red face of the mandrill, the face of the drill is uniformly black, relieved only by a bright red lower lip. The male drill also has prominent ridges to the side of his nose, but they are not grooved like those of the mandrill. The drill has wide black 'cheeks' to the side of his face, beyond which the face is surrounded by a white ruff. The white and black combination is very visually prominent, making a male drill identifiable and visible over a great distance in the forest interior. Indeed, the male drill is easily visible no matter which direction he is facing.

By contrast, the female drill is just a dull greyish-brown baboon-like monkey with a naked, blackish face. The grooves around her nose are much smaller and less pronounced than those of the male. In build she is much more slender, without the conspicuous mane. Male and female drills both have tails reduced to just a short stump. Although their almost-tailless appearance make them similar to apes, they are monkeys, quite closely related to baboons.

Forest Baboons

While the other baboons generally live in open country like savannah or (in the case of the Gelada) mountain grassland, the drill and the mandrill live in dense forests. They are still ground-living, spending most of the time feeding on the forest floor. They can climb trees, though, and will flee into them to escape from threats from below such as leopards. They will occasionally move out into open forest patches interspersed with grass.

Still, drills resemble the other baboons in being generalist feeders. They will take fruit, both from the tree or from the ground; they'll gather edible mushrooms; they'll dig for roots; they will take invertebrates like worms, snails, termites and spiders as they find them; they will also catch rodents, birds, lizards and other small vertebrate animals, and take the eggs of birds and sea turtles. They will also eat leaves, shoots and flowers.

They are also as social as other baboons. Drills usually roam the forest in small groups of about twenty. These will typically be led by a single, dominant male. There may be other adult males in the group, but they will be smaller than the dominant male and will submit to him. But most of the group will consist of females, these constituting a harem to the dominant male. These bands of drills roam the forest, every member employing eyes, ears and nose to find food. When a food source is discovered it is shared, but the dominant male often gets the lion's share. They move through their territories on the ground, but will climb into trees to gather fruit and other food. They also sleep in the trees. Their thickly padded buttocks help them to sit and sleep comfortably on tree branches.

A drill's face.

As drills move through the forest, they keep contact with each other by constant grunts. They will bark loudly to announce a predator or other threat. The dominant male serves as a beacon for the rest of his troop. He has glands over his chest that exude a secretion that he rubs on tree trunks and branches wherever he goes. He is, to the rest of his troop, the very embodiment of 'home'. The master drill is also a visual signal to the rest thanks to his bright buttocks and striking face. He will lead the troop's movement during each day's foraging. He will also keep other males in place by threat displays. He will bare his teeth, shake branches, and bob and tilt his head. During these displays the black face and white ruff are prominently shown off; head tilting also emphasizes the red lower lip. The head tilt can also serve as greeting, or appeasement between males.

Drills breed throughout the year. A female that is ready to mate gets a swollen, red backside. Only the dominant male mates with her. All subordinate males in the group have their sexualities repressed by the dominant male. As long as he is the boss, they remain in a somewhat sub-adult condition … they are smaller, their buttocks are not as bright, their faces and manes not as prominent.

A drill mother and baby.

Females have their babies spaced about six years apart. Drill 'children' are playful and mischievous. The youngsters tend to remain in the group after growing up. Young males willing to subordinate themselves to the dominant male can remain. The bigger, stronger and more aggressive males will however often be driven from the group. The males that are driven off can spend some time on their own, growing and getting stronger so that sometime later they, too, might challenge a dominant male of their own or another group. A male that is inside the group may also challenge the dominant male. This may happen if the dominant male gets old and weakens. Then, one of the other males may experience a surge of testosterone, this no longer being suppressed by the dominant male. The testosterone will cause the male to become much bigger and stronger; his mane will grow longer; his buttocks and genitals will intensify in colour; his muzzle will grow bigger, his face larger, the nose-ridges and cheek-flanges will enlarge and become deeper black. He will then be in condition to challenge the dominant male and, if successful, take his place.

But drills are often not very aggressive. Groups of them may meet other groups in the forest and team up for short periods, roaming around as bands of up to 200 animals.

As I've said, this is a highly endangered primate species. Drills are found only in the Cameroon and a small part of Nigeria, in a region of rainforest close to the coast. A separate subspecies of drill occurs on the island of Bioko off the coast of Cameroon. Drills have suffered greatly from the forests being cut down for lumber, and are also actively hunted for food as well as being exterminated by farmers who don't want them raiding their crops. The Korup National Park in Cameroon offers protection for at least some of them. Drills are also currently being propagated in a breeding program in Nigeria, and a small number are found in zoos all over the world. It will surely be a sad thing if we lost this highly unique species of monkey, so let's hope the conservation and breeding efforts succeed!

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