Drill, mandrill, or baboon?

Here at Zoo Atlanta, we are lucky enough to care for the only drill monkeys in North America. In the early 2000s, their Species Survival Plan (SSP) made the difficult decision to stop breeding, due to a lack of genetic diversity in the North American population. As time has passed and the population has grown smaller and smaller, it made sense for Zoo Atlanta to house the last members of the North America population together. Currently we are the only institution to house drills in North America, with our individuals; we have our one male, Enwe, and three females, Achi, Drew and Amaka. All four of our drills are related. Enwe, Drew, and Achi are all siblings, and Amaka is Drew’s daughter and Enwe’s and Achi’s niece. All are in their early 20s and will live the remainder of their lives at Zoo Atlanta, hopefully for another 10 years at least. However, because they are so uncommon to see in the U.S., we commonly hear guests confuse them for mandrills or baboons, which are much more common. However, drills are not mandrills or baboons; in fact, they are not even closely related to baboons, although they are closely related to mandrills.

Drills and mandrills are the only two currently living species in the genus Mandrillus, so think of them like species that are cousins of each other. They do share many of the same characteristics of each other, such as both being terrestrial monkeys that spend most of their time foraging on the ground of the rainforest. Both species also elicit the same behavior, called an affiliative grin; this is when they smile at one another as a friendly action. This is an odd behavior for monkeys, though, because they are two of a few species that smile as a friendly action. Most species see smiling as a threatening action.

Additionally, drills and mandrills both share the same type of social structure, with one or two adult males overseeing groups of many females and young males. Though they have similarities, they also have differences, which are range, conservation status, and physical characteristics. Mandrills are found rather broadly throughout western Africa in many different countries, while drills are only found in the Cross River state in Nigeria, southwestern Cameroon, Bioko Island, and a small part of Equatorial Guinea, and as such, have a much smaller range. In line with this, mandrills are classified as vulnerable by the IUCN Red List, while drills are considered endangered, meaning they are under a more severe threat of extinction. Lastly, while drills and mandrills look similar, there are a few distinct differences you can use to tell them apart. The biggest difference can be seen between males. Male mandrills have red and blue coloration on their noses, while male drills have no coloration on their noses and only have a red strip directly under their lips. In terms of females, the same rule applies, female mandrills have a colorful face, with that red and blue coloration on their nose and cheeks, while female drills have no extra coloration on their face.

Now that we’ve established the differences between the closely related drills and mandrills, let’s add baboons into the mix. Drills are not actually closely related to baboons. Although they look similar to many of the species, they are much more closely related to mangabeys, a species which looks nothing like drills but has similar diets and forearm morphology. In fact, when scientists looked at morphology and molecular DNA, they determined that mandrills and drills split off from baboons very far back in terms of evolutionary time. While drills and baboons share some common characteristics, such as both being terrestrial monkeys and having the same social structure, they have many more differences than similarities. One of the big differences is that there is only one species of drill, while there are five species of baboons. While drills are considered endangered, all five species of baboons are considered of least concern, which means they are not believed to be under threat of extinction any time soon. Baboon species are also found broadly across Africa compared with the small range of drills. The biggest difference between the two is their appearance. Because there are five different species, some species do look similar to drills with one big difference. No baboon species have the same bright coloration on their bottom lips and rear ends that male drills do, which is the easiest way to tell male drills and baboons apart from one another. Distinguishing female baboons and drills may be slightly trickier for someone who doesn’t know the difference, because female drills don’t have the same bright coloration as males, but they tend to have less hair on their noses, cheeks and around their eyes than the species of baboons that look similar to them.

Caroline S.
Keeper I, Primates