It's a boy! It's a girl! It's even better -- one of each " and both Amur tiger cubs, born Sept. 26, are doing grrrrrrrreat. At their latest check-up, the male cub, named Viktor, weighed 9.68 kilograms (about 21 pounds), while the female, named Talya, weighed slightly less at 8.2 kilograms (about 18 pounds). This weight difference between male and female is common. The cubs' names come from the Russian language, recognizing the Amur tiger TMs primary habitat in eastern Russia. Viktor's name means "conqueror" and Talya TMs name means "birthday." Both Viktor and Talya will remain with their mother, 8-year-old Marta, for at least two years. Dr. Randi Meyerson, curator of mammals, emphasized Marta TMs continuing excellent maternal behavior as a key factor in the cubs' health. "Both cubs continue to gain in weight and mobility, which is a reflection of Marta TMs outstanding care so far," she said. "We are cautiously optimistic about their future progress." Viktor and Talya are showing increasing confidence and coordination as they explore their off-exhibit quarters. As they grow, they are playing more and sleeping less; one of their frequent games is to pounce on their mother TMs tail or climb on top of her when she lies down. Their appetite is increasing, too, and they have tasted some of the solid food from Marta TMs dish, though they will continue to nurse for several months. The cubs are not scheduled to go on exhibit until some time in January 2012. These initial months allow the cubs to become fully mobile and have full protection from their initial vaccinations; weather and exhibit conditions could also affect the date of their public introduction. Amur tigers, formerly known as Siberian tigers, are the largest tiger subspecies, and about 143 Amur tigers live in about 53 AZA-accredited zoos. Originally, eight subspecies existed; three of those subspecies are now extinct. The five remaining subspecies, including the Amur tiger, are critically endangered due to habitat loss and fragmentation as well as poaching of both tigers and their prey.