When Natalie and Tuck first arrived at the National Zoo, their neighbors, the gazelles and the oryxes, were too scared to walk by their stall, such horrid noises did they make.

Plus, their diet was unsettling — dead rats and rabbits, and beef bones. They also tended to drool and stand on their food when they dined. And they had a habit of burping up hairballs.

But they were vultures, after all. And although they had reptilian feet and menacing beaks, they had a gentle look in their eyes. And they were only a threat if you were dead, or nearly so.

Technically, they are endangered Ruppell’s griffon vultures, native to sub-Saharan Africa. They arrived from another zoo over the summer and made their debut recently. The zoo is now trying to acclimate them to their neighbors and their keepers.

“We’re trying to work them into a mixed-species exhibit,” said Kate Volz, an animal keeper who handles the vultures. “They’re getting along really well with our gazelles so far, but not so well with our oryx, so it’s still a work in progress.”

She said the keepers are trying to train the vultures to come inside from their outdoor enclosure when summoned, but that’s a work in progress, too. The big birds are stubborn, nimble and elusive.

They can be lured with bits of meat, as they were during training Thursday. Often they must be shooed in with a broom.

The zoo puts new animals through a period of medical quarantine, to make sure they’re healthy, and then gradual socialization as they go on exhibit.

The keepers try to vary the diet of the vultures, who, in the wild, eat carrion.

They have a “rat day, rabbit day and bone day,” Volz said. On rat day, they each get three dead rats. On rabbit day, they each get a single dead rabbit. Bone day features beef femurs with flesh still attached.

“They like to rip things apart,” Volz said. “You know, like a carcass. . . . They enjoy bones . . . and bunnies are good, too. Bunnies are popular.”

There is also a “meat day” when the pair are served a product that resembles liverwurst.

The zoo’s new vultures have clipped wings and can’t fly. But Ruppell’s griffon vultures in the wild are known to cruise at 20,000 feet, and one once struck a jet flying at more than 30,000 feet, the zoo said. They have superb vision, mate for life and have been known to live for 50 years.

Natalie and Tuck are handsome birds with long, snake-like necks and heads that can swivel 180 degrees, so they can get inside carcasses.

They have beaks like a turtle’s, brown-gray feathers on wings that can span eight feet and a “ruff” around the neck like a feathered boa. They weigh up to 20 pounds, and stand more than three feet tall.

The zoo sought the vultures because it wanted to diversify its Cheetah Conservation Station complex, which includes an array of animals and had an available stall.

“We thought, ‘What can we fit in this stall?’ ” Volz said. And what species would be compatible with its neighbors?

“We arrived at the Ruppell’s griffon vulture,” she said. “They’re a pretty hardy bird. They get along well with hoofed stock, in general.”

The birds came in July from the Fort Wayne Children’s Zoo in Indiana and are getting adjusted to their community. They are about a year and a half old, Volz said.

The vultures are vital to the ecosystem, experts say, because they help dispose of dead animals, and their stomach acids destroy such organisms as anthrax, cholera and botulism.

They can also be rowdy and willful.

Their vocalizations were the things that initially disturbed the neighbors.

“They do this ‘ack, ack, ack ack,’ ” Volz said. “Then they can do this ‘haaaaaaah,’ ” and an “eeeeeeeee” that she said sounds like the Dementors that suck souls out of people in Harry Potter movies.

At first, in the evenings, the other animals would not walk past them to reach their stalls, Volz said. “They didn’t even see them yet,” she said. “They were just hearing them.”

Eventually, the oryxes and gazelles got over their fear.

But the keepers still had difficulty getting the vultures to come in at the end of the day.

The keepers had some success with “target training,” in which pieces of meat are placed on a blue Frisbee attached to a pole. The keepers then enter the enclosure and try to lure the birds to the stall with the target.

But that didn’t always work. The vultures would come only so far, then run off.

“These guys aren’t there yet,” Volz said. “Our goal is to have them come in just by training. We’d rather they came in when we call them.”

How do you call a vulture?

“They might know their names,” Volz said. “It’s hard to tell.”

Friday afternoon, the two birds were lured partway to the stall with the Frisbee-meat-on-a-pole apparatus but kept bolting at the last minute.

Volz and fellow keeper Gil Myers persisted. They coaxed and lured. “Come on, Natalie,” Myers said.

Out of meat, the keepers turned to “shifting” brooms, used for herding animals. Tuck went in first.

Natalie remained outside. As the keepers maneuvered her toward the stall, Volz asked, “You gonna go in, sweetie? Come on.”

Finally, the bird complied.

Inside the inner stall, the keepers had placed cardboard boxes and tubes filled with shredded paper and meat. The vultures tore into them.

After a few minutes of rending and ripping, the birds paused, and Volz addressed them cheerily: “Was that fun?”