Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers take rest at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)

Siberian tigers are seen at the Siberian tiger zoo in Hailin, northeast China's Heilongjiang Province, Dec. 10, 2015. The facility, the world's largest Siberian tigers breeding center, is home to over 1,000 Siberian tigers, among the world's most endangered species. (Xinhua/Qiang Yong)