MEXICO CITY – The first known litter of Mexican gray wolves has been born in the wild as part of a three-year effort to re-introduce the subspecies to a habitat where it disappeared three decades ago, Mexican officials reported Thursday.

Mexico’s National Commission for Natural Protected Areas said the wolf pups were sighted in June by a team of researchers in the western Sierra Madre mountains.

“This first litter represents an important step in the recovery program, because these will be individuals that have never had contact with human beings, as wolves bred in captivity inevitably do,” the commission said in a statement.

It said the pups appeared to be doing well.

Mexico began reintroducing wolves in 2011, and the parents of this litter had been released in December with hopes they would reproduce. Authorities seldom reveal the exact location of breeding pairs in recovery programs, to protect endangered species.

The Mexican gray wolf remains an endangered species in the United States and Mexico.