Six Mexican wolves born on April 7, 2019, in captivity at the Endangered Wolf Center in Eureka, Missouri, were taken to live with packs in Arizona and New Mexico.

(Rachel Crosby/Endangered Wolf Center via AP)

At a Glance

The six newborn pups are placed into packs that had litters about the same time.The foster programs increases genetic diversity in the species of which only 150 remain in the wild.Three wild pups were returned to the Endangered Wolf Center to be fostered by captive parents.

Six critically endangered Mexican wolf pups born in captivity have been placed in packs in the wild in Arizona and New Mexico.

Having the 11-day-old pups fostered by wild parents increases the number of Mexican wolves in the wild and , according to a news release from the Endangered Wolf Center, which runs the fostering program.

"It is literally vital for this particular population," Regina Mossotti, director of animal care and conservation at the Endangered Wolf Center, told the Associated Press on Thursday. "When you're talking about 150 animals left in the wild, genetics plays a crucial part in whether that recovery effort is successful or not."

In the 1970s, because of hunting and habitat loss, the number of Mexican wolves fell to seven. Those wolves were captured by the U.S. Wildlife Service and put into managed care programs for breeding and recovery.

Captive-born wolves were first returned to the wild in Arizona and New Mexico in 1998, according to the Endangered Wolf Center. Now the population has grown to 150, including about 20 in Mexico.

This is one of the six Mexican wolves born on April 7, 2019, in captivity at the Endangered Wolf Center in Eureka, Missouri, that were taken to live with packs in Arizona and New Mexico.

(Rachel Crosby/Endangered Wolf Center via AP)

Timing plays a key role in fostering wolf pups. The captive packs and the wild packs have to have litters within a few days of each other, and the placement has to happen before the pups are 14 days old so that the foster mothers accept the new pups.

“Everything has to line up … the stars, the sun, the moon, and the planets all have to align to make a foster happen,” Mossotti said.

Vera and Mack had a litter of nine pups at the center in Eureka, Missouri, on April 7. The Prime Canyon Pack in Arizona and the Frieborn Pack in New Mexico had litters at the same time.

Mossotti and two colleagues, Erin Connett and Rachel Crosby, flew six of Mack and Vera's pups — three male and three female — to Arizona on April 18, AP reported.

Regina Mossotti, left, director of animal care and conservation at the Endangered Wolf Center, and U.S. Fish and Wildlife biologists Cyrenea Piper, center, and Allison Greenleaf prepare Mexican wolf pups born in captivity at the center to be relocated to wolf dens along the border of Arizona and New Mexico.

(Rachel Crosby/Endangered Wolf Center via AP)

With help from Arizona Game and Fish and the U.S. Fish and Wildlife Service, the women got the wolves to their new homes.

One female pup was left with a litter of seven pups in Arizona. The five remaining pups were taken to a pack in New Mexico that already had six pups. To avoid overburdening the mom, three of the wild pups were taken back to the Endangered Wolf Center to be fostered by Vera and Mack.

Mossotti said the wild mothers appear to have accepted the new pups.

"They get a bad rap," she said. "We're used to seeing on TV the 'big bad wolf,' the big scary animal, which ironically is the opposite of what they are in real life."