SALT LAKE CITY — Silverback gorilla Husani is balancing a branch in his mouth, cautiously eyeing the corner where his roommate, Tino, sits in the shade.
Husani marches through the tall grass until the two massive silverbacks are facing each other, averting their gaze. Lips pursed, chests puffed, it's a dominance display, and 18-year-old Husani is hoping to win in a war of testosterone against 37-year-old Tino.
In a blink, Husani whips the branch out of his mouth and into the air, immediately retreating back through the grass after the branch cracks with a loud snap.
Tino holds his ground.
These are heart-pumping antics to watch from safety behind a Plexiglas wall or fence. While male silverbacks jostling in the wild is common, it's a different story in captivity. Hogle Zoo has become only the second zoo in the nation to successfully cohabitate a pair of adult silverbacks.
"It's quite a long and challenging process," said Erin Jones, the zoo's senior gorilla keeper. "We've had to go really slow and let the boys decide when they're ready to take the next step."
Since Husani's arrival in May, zookeepers have kept a close eye on the silverback pair. Tino was immediately interested in Husani, staring at him between enclosures, the two displaying their bravado when passing one another.
"Basically, they didn't want to be apart," Jones said.
Zoo volunteers track Husani's behavior in detailed reports, writing down observations every three minutes, keepers gauging when and if the 300-plus-pound primates will be ready to cohabitate.
Two weeks ago, Husani and Tino were officially introduced in the indoor enclosure. Zookeepers film their interactions, from brief two- to 15-second wrestling matches to Wednesday's power struggle. They study the footage, the daily logs and even research from the Jacksonville Zoo in Florida, the first zoo to cohabitate silverbacks.
It took the Jacksonville Zoo seven years to get a pair of silverbacks to live together. They began with a set of four solitary silverbacks, slowly allowing them to interact through mesh between enclosures, then gradually introducing different pairs and combinations.
One died from an unrelated drowning accident, and another never got along with the others. But in 2005, 33-year-old Lash and 26-year-old Rumpel formed the first captive bachelor pad.
"It was something no one else had done before, so it was uncharted territory," said Tracy Fenn, the zoo's mammal supervisor. "I don't think every silverback combination is a good match. A lot of it has to do with personality of the individual."
In their native Africa, the endangered species live in packs of five to 30, with one dominant male heading up a group of females and their offspring. Young black-backs leave the group after puberty. Some kidnap or coax away other females to make their own group, but more often, male silverbacks live in bachelor troops.
"Bachelor groups are a necessity in the captive population because of the surplus males," Fenn said.
Today, most zoos try to form bachelor groups when the male black-backs are young, rather than a mature adult. "The gorilla management community didn't realize that was a necessity back in the day," Fenn said.
Indeed, even the American Zoo Association's Species Survival Plan, biographical information kept on each zoo animal, adds a new layer for gorillas. Listing genealogical history, a who's-mated-with-who directory, the gorilla's SSP plan highlights social interactions.
"It's a complex picture. Just like in the wild, not every male can be the main silverback," said Steve Feldman, AZA spokesman. Bachelor groups "are an increasing need. Now, it's a question of finding the right individuals to live together in harmony."
So far, Husani and Tino have been together for two to four hours at a time, occasionally bluff-charging each other or beating their chests. The ultimate goal is that the two will be good buddies, forming a brotherly bond.
Husani is now eyeing Tino's shady corner again, the one against the glass where the silverbacks can watch zoogoers and vice versa. Tino has wandered off, sitting in a new shady spot by a small creek meandering through the west end of the enclosure. But this doesn't stop Husani's showmanship. He approaches with a cardboard box in hand, charging the spot and throwing the box in the air.
He turns around and sits, proud that he's now commanding the coveted spot — or anxiously awaiting Tino's return.