Two red-crowned cranes have lunch in their den in the Chengdu Zoo in Sichuan province. On the wall is a reed lake which is their natural habitat. [Photo by Huang Zhiling/chinadaily.com.cn]

Two red-crowned cranes are having lunch in their den while a flock of sparrows fly in to share their food.

Visitors keep taking pictures or simply stand quietly outside to observe the birds.

It's just another day at Chengdu Zoo in Sichuan province. But Li Xiao felt a pleasant surprise when she visited the zoo with a friend from Austria on Tuesday.

They had planned to see giant pandas. But when they arrived at the panda house, it was closed because it was being refurbished.

"We had been in a mood before we arrived at the den of the red-crowned cranes. The peaceful coexistence of different birds has cheered us up. We liked the painting on the den wall. The reed pond in the painting is so true-to-life and we almost mistook it for the cranes' natural habitat," Li said.

The last time Li visited the zoo was 12 years ago.

"All the den walls were white and monotonous. But now, they have beautiful paintings which resemble animals' natural habitats," she said.

The Chengdu Zoo which opened to visitors in 1976 is the largest zoo in Southwest China and displays more than 300 types of rare animals including pandas and Manchurian tigers.

The zoo has invested nearly 100 million yuan ($15 million) in the past decade to build larger dens and playgrounds for animals and a forest covering 2,850 square meters for some 500 birds decorate the den walls, according to deputy zoo chief Jing Shimin.

"Art students from Chengdu University of Technology and Chengdu University have been invited to decorate the den walls with paintings," he said.

Visitors were impressed with the vivid paintings of mountains and rivers on the walls in the dens of tigers and the golden eagle and grassland for the African lions' dens.

"Animals' true living environment has been introduced through the paintings. For example, the Changbai Mountain has been painted on the wall of the Manchurian tigers' den," said Wang Qiang, head of the Chengdu Zoo.

The efforts to improve the environment have paid off as the zoo has drawn an increasing number of visitors.

Some 2.8 million people have visited the zoo this year, an increase of more than 100,000 people over the previous year, said Jing.