Arizona Center for Nature Conservation/Phoenix Zoo

The Arthur L. and Elaine V. Johnson Conservation Center at the Phoenix Zoo has announced the birth of a bumper crop of 21 black-footed ferrets.

The Arthur L. and Elaine V. Johnson Conservation Center at the Phoenix Zoo has announced the birth of a bumper crop of 21 black-footed ferrets.

The animals are one of North America's most endangered species.

The four litters join the more than 500 kits born during the Zoo's 30 years of black-footed ferret breeding, and more births may be on the way.

The newborns will stay with their mothers inside special boxes designed to mimic ferret dens.

Once thought extinct in the wild, black-footed ferrets have been reintroduced to eight grassland ecosystems in the U.S. and Mexico, including Aubrey Valley in southwest Coconino County.

Habitat loss and diseases like plague still threaten their recovery in the wild. 

Arizona Center for Nature Conservation/Phoenix Zoo

Black-footed ferrets emerge from a tunnel in a cage designed to mimic a ferret den.