In the winter of 2012 on the Sino-Russian border, the Wusuli River was covered with thick ice when a female brown bear with two cubs strolled across the river and into China seeking food.

This is just one of many media reports of wild animals crossing the border as the eco-environment between the two countries continues to improve and animal populations recover.

The eastern section of the border extends for more than 4,300 kilometers. Primitive ecological forests and abundant water resources in the area are an excellent environment for wild animals. China and Russia set up an action plan in 2012 to cooperate on protecting Siberian tigers and leopards.

The current wild population of Siberian tigers is less than 500, mainly scattered across the far Russian east and through northeast China's mountain forests. With a population of around 20, Amur leopards are listed as critically endangered on the International Union for Conservation of Nature Red List of Threatened Species. Most of them live in the border region.

In June this year, a fisherman on the Wusuli River accidentally met a wild Siberian tiger which was crossing the river and tried to climb aboard his boat. He used a paddle to repel the tiger and filmed it swimming ashore on his cellphone. The story attracted great interest when the video was published online.

Jiang Guangshun, professor with the Northeast Forestry University, believes that these border crossings are a good sign showing that populations are expanding, and symbolizing the improvement of Sino-Russian cooperation in protecting the tigers, which seem to be spreading into northeast China, as Russian habitats tend to be overcrowded and the environment is recovering in China.

Honghe National Nature Reserve in Heilongjiang signed a five-year cooperative agreement with Russia's Khinganskiy Nature Reserve in 2008. Having been to Russia several times, Dong Shubin, head of the Honghe reserve, thinks China has a lot to learn from Russian conservationists. This year, Honghe also signed a deal with Bastak Nature Reserve to exchange information on rare birds and wetland research.

The cross-border Xingkaihu Nature Reserve, established in 1997,is the breeding ground for many animals and an important habitat for migratory birds. Protection of the Xingkaihu biosphere is a job for both sides. Xingkaihu wetland research station holds symposia with Russian counterparts every year.