They’re rowdy and aggressive. They make a lot of noise. They rarely clean up
after themselves and they’re obsessed with females. This might sound like your average college fraternity but it also describes gorillas living in all-male bachelor groups. Describing the bachelors is easy—but dealing with them is another matter.

In zoos, as in the wild, adult male gorillas typically live in polygamous family groups with five to six females and their offspring. As male offspring mature, they set out on their own in search of mates. The quest for mates isn’t always successful, however. Because male and female gorillas are born in equal numbers, not every male can have five or six females to himself. Without a harem of their own to call home, some single males in the wild form loosely knit bachelor parties. In zoos, managers cope with the oversupply of male gorillas by forming bachelor groups and maintaining them in their own exhibit space.

“The challenge with maintaining bachelor groups in zoos is that they often fall apart because of personality conflicts and aggression,” explains Lisa Faust, a population modeler in the zoo’s Alexander Center for Applied Population Biology. Zoos are trying a number of different strategies to keep the bachelor groups stable over the course of the animals’ 50-year lifespan. One promising technique gives the bachelors a sense of privacy by creating visual barriers in the exhibit space. Out of sight can often mean out of mind when an unruly gorilla is looking to pick a fight with a fellow bachelor.

Since bachelor groups require specialized exhibit features like the visual barriers, zoos need to know how many bachelor groups they can expect to house in the future. Faust is developing a computer model of the captive gorilla population to predict how many bachelor groups will be needed. The model results will then be combined with analyses conducted by scientists at the zoo’s Population Management Center to ensure that the captive population remains genetically diverse. Young males from rare family lines make good breeding candidates, while those with relatively common genes will likely be designated lifelong bachelors.