Calaya, the National Zoo’s 15-year-old western lowland gorilla, is awaiting the birth of her first baby. (Matt McClain/The Washington Post)

The first time Baraka saw Calaya, something clicked.

The first time they got together, sparks, and maybe a little zoo straw, flew.

Now Calaya, a 15-year-old female western lowland gorilla at the Smithsonian’s National Zoo, is about to have her first baby. Baraka could have his first surviving offspring.

And zookeepers and much of the gorilla community are awaiting the birth of what will be the first baby gorilla there in nine years.

“She’s very pregnant,” Melba Brown, Calaya’s primary trainer, said Thursday at the zoo, before helping to conduct an ultrasound to check on the baby’s health. “We are literally in the birth window.”

The two gorillas have been a power couple since Calaya arrived three years ago. The zoo has six gorillas.

Baraka, 25, is a “silverback,” so called because of the gray hair on his broad back. He weighs about 425 pounds, Brown said, and is in overall charge in the gorilla enclave. He mediates disputes within his troop and decides on everyone’s bedtime.

Calaya weighs about 205 pounds and is the dominant female in her group.

The infant will probably weigh a scrawny four or five pounds. “It’s very small,” Brown said. “They tend to have spindly legs.”

Calaya was initially on birth-control pills when she arrived at the zoo in 2015 from Seattle’s Woodland Park Zoo.

“We let her come and get acclimated to the group, kind of figure out what her position would be,” Brown said. “Once we were certain her health was in the perfect state to have a pregnancy, we took her off birth-control pills.”

She became pregnant in August. The zoo verified that using a standard human pregnancy test.

As zoo experts reached through grid fencing to perform the ultrasound Thursday, Baraka swaggered about, with his forbidding visage and considerable bulk.

Despite his tough-guy look, he is said to be a mild-mannered creature.

“He’s very laid back,” said Becky Malinsky, assistant curator of primates. “He’s the most laid-back male gorilla I’ve every known. He’s a delight.”

Gorillas mate about once a month, Malinsky said, unlike some other animals that do so only once a year.

Calaya and Baraka hit it off right away, Malinsky said, and mated within an hour of physically meeting for the first time. “It was love at first sight,” she said.

Even before they met, when he could gaze at her only from behind the glass of the enclosure where she was temporarily quarantined, she caught his eye.

“We’re pretty certain that Baraka was taken by her, just based on his behaviors,” she said.

Malinsky said keepers decided to introduce her to him first, before they introduced her to the others.

“It was a very smooth introduction,” she said.

This was in 2015, while she was still on birth control, but it was promising for the future.

A gorilla’s gestation period is 7½ to 8 months.

Keepers are not sure how Calaya will react to giving birth. “She’s very new at this,” said Brown, her trainer. (Baraka fathered an offspring at another zoo, but it died.)

Calaya may be stunned. But Brown has done some maternal training with her using a stuffed gorilla toy standing in for her baby.

“So she knows what it means to kiss her baby, to touch her baby, and to feed her baby,” Brown said.

“Let’s say she gives birth and she leaves it alone for an extended period of time,” Brown said. “I can potentially say, ‘Calaya, pick up your baby,’ or ‘Calaya, feed your baby,’ or ‘Bring it over to me.’ ”

Brown said Calaya understands when the trainer speaks to her. Hand signs can also be used. “You have no idea,” she said. “They understand a lot. . . . They absolutely understand words.”

As for Baraka, “he has an extremely playful side,” Brown said.

“He knows where everybody is,” she said. And he comports himself well.

“If he’s right at the door to go outside . . . and he knows there’s something really good outside, like popcorn,” he will stand back and wait for the others to go out first, Brown said.

“He’s a gentleman,” she said. “He really is. . . . He’s a protector. . . . His really significant role is, if there was a female squabble, he will stop it.”

Sometimes he gets between the two parties to break up the fight.

Sometimes he will just shoot a look.

And when the baby is born, he will be involved.

“Everyone has this image of a silverback ‘King Kong,’ ” she said. “Get rid of that image.” The low growling he emits is what’s called a “pleasure rumble,” a sign of contentment.

“This is his family,” Brown said. “It’s going to be expanding by one. . . . He is very aware of what’s happening.”