Drill

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Drills’ cheek pouches expand for storing food short-term and can hold as much food as the stomach.
Their rump color is not pigment, but a combination of blood vessel activity and the reflection of light. It becomes more pronounced when the animal is excited and may act as a beacon to enable the troop to stay together in dim forest. The hue also gets brighter as an animal attains maturity and rank.
Drills are highly sexually dimorphic. Males weigh 80-110 pounds while females weigh 30-45 pounds. Males have an area of red skin between the lower lip and chin and long canine teeth (1½-2 inches). Males also have a large mane.

Range – only found in Southwestern Cameroon, Nigeria, and the West African island of Bioko (a part of Equatorial Guinea)
Habitat – lowland, coastal, and riverine rainforests

Wild – various forms of plant matter, nuts, as well as fruits, insects and small invertebrates
Zoo – apples, bananas, oranges, grapes, mango, melon, kiwi, grapefruit, and primate chow; When available, they get banana leaves. Our drills eat a wide variety of vegetables including carrots, collards, squash, and beans, peanuts, fruits, bamboo, or other non-toxic approved browse. They may also eat insects and spiders in the exhibit.

Males are sexually mature at 5-7 years and females at 4-5 years.
Females have pronounced swelling of their perineum about every 33 days. Swelling takes about 1 week to become full size, estrus will last about 3 days, and then the swelling will diminish in another 3 days.
Young are born seasonally. Birth season is thought to be between December and April.
Gestation: 5½-6 months
They usually have a single baby. Twins are rare, as it would be difficult for the mother to carry 2 infants rapidly through the forest.
In the wild, females will usually not breed again for 2-3 years after giving birth.

Major threats: Hunting, habitat loss due to clear-cutting
Drills are the most endangered monkey species in Africa. Listed by IUCN as highest conservation priority of all African primates.
Numbers only about less than 3,000 in the wild.
Dr. Dietrich Schaaf, former director of collections at Zoo Atlanta, and Dr. Tom Butynski, conservation biologist, have conducted primate surveys in the interior of the island of Bioko. Hunting seemed to increase between 1990 and 1992. Wild studies of social and reproductive behaviors will improve captive management and husbandry techniques.
Drill Ranch in Calabar, Nigeria rescues drills and breeds them on site and at a site at Afi Mountain, where drills may be released in the future.
Many of the adult drills in North American zoos today were hand-reared as infants, leading to behavioral deficits which resulted in poor mating and parenting skills. This is why there are so few drills in zoos, and why the captive population itself is in danger of extinction. Zoo Atlanta housed the last reproducing drill group in North America. Although, now they are no longer a breeding group.

Drills walk on the flat surfaces of their feet and hands, not their knuckles as apes do.
They exist in multi-female troops with one or more males totaling 20 or more animals. There is one dominant male per troop.
They communicate through a variety of deep grunts and sharp cries, as well as body movements such as lip smacking, grimaces, and teeth displays.
Presenting the rear is a sign of submissiveness or solicitation. Females and youngsters will display to the dominant male and even the keeper; males will present for grooming.
Predators: Leopards and other large carnivores

Nowak, R. M. (Ed.). (1983). Walker’s Mammals of the World: Ed. 2, Vol. 1 (pp. 456). Baltimore: Johns Hopkins University Press
ARKive Images of Life on Earth (2004). Drill. Retrieved October 16, 2004, from: http://www.arkive.org/species/GES/mammals/Mandrillus_leucophaeus/more_info.html
Columbus Zoo (2004). Drill. Retrieved October 16, 2004, from: http://www.columbuszoo.org/animalareas/aforest/drill.html
Animal Diversity Web: http://animaldiversity.ummz.umich.edu/accounts/Mandrillus_leucophaeus/

Updated July 2020