While some wild-born cubs were placed with a wolf pack at Brookfield Zoo, puppies born at the zoo joined a wild pack of wolves in New Mexico. According to Brookfield Zoo, this fostering technique improves the demographic and genetic diversity of the Mexican gray wolf populations in the wild and in professional care.
Mexican gray wolves are the rarest subspecies of gray wolves in North America. They were considered extinct in the wild until their reintroduction into Arizona and New Mexico in 1998. By 2016, less than 400 Mexican gray wolves were left in the world. Killing a Mexican gray wolf is a violation of the federal Endangered Species Act.