Indoor enclosures occupied by other animals that are accustomed to hot weather, such as giraffes, elephants and hippos, are fitted with heaters that keep the temperature above 15 C.

Giraffe keeper Hu Jun said the heaters are turned on at 4:30 pm and switched off in the morning.

"Turning off the heaters is not a way of saving money," said Hu. "We hope it will encourage the animals to go outside to get some sunshine during the daytime. Walking around improves their health."

Wall-mounted heaters are not suitable for all the animals.

"The orangutans used to damage the heaters and this stopped them from working, so we have to use underfloor heating to keep the temperature above 20 C," said keeper Dou Haijing.

"We also put straw on the floor, and the orangutans bury themselves in the straw if they still feel cold. They look really cute when they do that," Dou added.

Hippos keep warm in a heated indoor pool where the water temperature is maintained above 18 C.

The pool is used from late November, and the water is changed every three days. Before then, the hippos spend most of the day in an outdoor pool, and on cold days keepers raise the temperature by boiling water and pouring it in.

In addition to making sure the animals stay warm, the zoo prepares special kinds of forage and a winter menu to encourage them to eat properly.

cangwei@chinadaily.com.cn