The smallest of eight red wolf pups born at Point Defiance Zoo & Aquarium this week has died. Zoo officials discovered the dead female Thursday morning. The cause of death is unknown.

The pups' mother, an 8-year-old named Millie, appears to be taking good care of her remaining seven offspring -- four males and three females -- said Will Waddell, the zoo's Red Wolf Recovery program coordinator.

Red wolves are one of the most endangered mammals on earth. The wild population numbers only about 100, all living along the coast of North Carolina. The Tacoma zoo is a key breeding facility in the ongoing effort to save the species from extinction.

The public should be able to see the newborn pups in a few weeks, when they venture out of their den.