Published Winter 2007

Near the end of adolescence, when most children move away from home to attend college or get jobs and rent a place of their own, parents say their offspring have “left the nest.” It’s not surprising that we borrow that term from the animal kingdom, since animals experience the process of adolescence in many of the same awkward and awesome ways we do.

While birds literally leave the nest, perhaps the most interesting zoo animals undergoing adolescence are primates, likely because they so closely mirror our own process of maturation. “Adolescent primates are a handful no matter what species you’re talking about,” chuckles Curator of Primates Sue Margulis, Ph.D., who doesn’t exclude her own 12-year-old daughter from that statement.

Signs of Adolescence
The changes of adolescence are spurred by hormones working silently within the body, but the outward physical changes are obvious. Most primates experience a growth spurt at the onset of adolescence. Testes descend in males; females begin cycling.

Male DeBrazza’s monkeys grow a prominent beard. Female white-cheeked gibbons’ coats switch from black to buff. And both sexes of gorillas and chimpanzees lose the tuft of white hair on their rumps that had quite literally served as a white flag—I’m just a kid! You can’t treat me as harshly as the adults!

Just as bodies change, so too do inter-animal dynamics. “If you’re talking about an asocial species, going through adolescence isn’t going to affect anybody else,” says Supervisor of Behavioral and Cognitive Research Steve Ross. “But with very social animals, relationships are important, so any deviation from normal has repercussions. If someone starts challenging an established hierarchy, things begin falling apart very quickly.”

Early in adolescence, tests of power, particularly by young primate males, are brushed off. Recently at Busch Gardens Tampa Bay, Ross watched a punky 7-year-old male chimpanzee pester a female for four straight hours without incurring the wrath of the group.

But as chimpanzees, gorillas and other primates get closer to adulthood, transgressions are less easily overlooked and the rules and repercussions of ape society are either learned or pounded into young minds.

Reproductive Competitors
Adolescence signals the start of sexual viability, and that entails a host of changes in the way young individuals are treated within primate groups. Previously uninterested and unable to breed, primates at the cusp of maturity recognize the opposite sex as more than playmates or caregivers. When male chimpanzees begin adolescence at around age 6 and start attempting to breed older females, as 7-year-old Optimus is currently doing at the Regenstein Center for African Apes, the dominant male (Hank in this case) will thwart those attempts. (He’s not always successful, says Ross.)

In other species, such as cotton-top tamarins, adolescent females’ cycling will be hormonally suppressed when in the presence of adult females. It’s a physiological way of preventing inbreeding.

Cubs to Contenders
Of course, in addition to primates, other species experience the physical and social changes brought about by adolescence. Young male lions begin growing a mane and experience a growth spurt that has them resembling the adult male in their pride. Of course, they still lack the muscle mass to challenge the leader.

At Regenstein African Journey curators and keepers closely monitored the male pygmy hippo’s development, trying to determine when to introduce him to the mature female. “That was a potentially aggressive encounter that was mitigated by waiting until the time was right,” says Curator of Mammals Dave Bernier.

At the Pritzker Family Children’s Zoo the juvenile black bear is testing social boundaries with the adult male and female in his exhibit.

Leaving Home, But Where to Go?
When animals in the wild reach adolescence they often leave—or are kicked out of—the family group. For example, when adolescent male lions are pushed out of the pride (a common trend across species that Bernier humorously refers to as “forced dispersal”), they frequently form bachelor groups, learning the skills and gaining the strength they’ll need to lead their own pride someday.

But in a zoo setting it’s not possible for a young lion to leave its exhibit and wander the savanna in search of new turf. “When you have young offspring, they basically live together as a group,” says Bernier. “Once adolescence hits, you cannot house the offspring with the parents, because either the adult male or female might become aggressive toward them. So you have to separate. Now instead of housing one group, you’re housing two or three. And that’s a problem of space for most zoos.”

To deal with space concerns, zoos cooperate with each animal’s Species Survival Plan to schedule births in order to mitigate overcrowding and enable transfers of animals to other zoos at stages of development that mirror life changes in the wild.

“Animals are commonly held at the institution where they were born until they reach adolescence,” explains Bernier. “So when you get approval to reproduce a species, you have to be willing to take on a commitment of years, potentially.”

As it is with humans, adolescence itself is a commitment of years—adulthood isn’t easy to achieve, after all. Whether it’s birds leaving the nest, chimpanzees testing social rules or lions flexing newly developed muscles, the process of maturation is strangely similar to our own.

In a zoo setting the changes in management prompted by adolescence are dictated by science and benefit both animal and institution. But those who’ve grown close to animals that must be transferred to begin their adult lives elsewhere—zoo staff like Margulis, Bernier and Ross—can’t help but suffer a little empty-nest syndrome.