These images made from video provided by the Minnesota Zoo on Friday show an Amur leopard with her cubs in the maternity den of the zoo in Apple Valley, Minn. The cubs, born May 29, join an estimated 90 Amur leopards living in captivity in the U.S. The species one of the most endangered cats in the world. Fewer than 40 are left in the wild. There have been no successful efforts to release captive-bred Amur leopards into their natural habitat in eastern Asia.