Three litters of American red wolves, which are critically endangered and number less than two dozen in the wild, have been born at the North Carolina Zoo.

The zoo said the litters, which total 12 pups, were born over three days at the end of April.

All the pups and their mothers are healthy and doing well, the zoo added.

The newest pups bring the total number of red wolves currently in the zoo’s breeding program to 36, making it the second-largest pack in the US after Point Defiance Zoo and Aquarium in Tacoma, Washington, according to the North Carolina Zoo.

Zoo officials said only 15 to 20 red wolves remain in the wild, all in eastern North Carolina, and they are considered the most endangered canid in the world.

One litter was born on the red wolf public habitat and the pups most likely will be visible starting in mid-June, when they begin to venture outside of the den.

The wolf family will be moved to the non-public breeding area when the pups are older and weaned from their mother.

The other two litters were born in non-public viewing areas of the zoo, officials said.