As of mid-May, a combined 18 Siberian tiger cubs have been born at the Siberian Tiger Park in Harbin and the Hengdaohezi Siberian Tiger Park in Mudanjiang, both in Heilongjiang province.

The parks are two of three run by the China Hengdaohezi Feline Breeding Center, the world's largest such facility for these rare tigers. The third is located in Shenyang, Liaoning province.

Siberian tigers are among the world's most endangered species. They mainly live in northeastern China and eastern Russia.

Mating season for the big cats usually falls in January and February, and the birthing period runs from early April to late June.

Two weeks after their births at the Hengdaohezi Siberian Tiger Park on May 1, five cubs — three males and two females — were getting stronger.

"Their mothers are three young tigers that have no experience nursing, so the breeders have taken on the task of feeding the cubs," said Zang Yingying, a breeder at the park. "The cubs' body temperatures dropped rapidly because their mothers did not take care of them after giving birth, so they had to be sent to incubators.

"They needed to be fed milk every three hours for the first week after birth," she said, noting that the milk was made from a formula powder for tigers. "Now they are fed every four to five hours with milk and eggs."

After days of careful nurturing, the five cubs were in good health and have been removed from the incubators. "Their average weight climbed from about 1.3 kilograms each when they were born to more than 2 kg on May 16," said Zang. "When the cubs are older, they will be fed chopped meat."