The animals missed their key feeding periods for two years in succession.' Picture: Sergey Kolchin

'In 2015, across almost the entire area of cedar broad-leaf forests there was a simultaneous bad harvest of nuts and acorns, in Khabarovsk and Primorsky regions.

'In 2016 this was repeated in Khabarovsk region. The lack of autumn food for two years in a row is an abnormal phenomenon which has turned into tragedy for the black bear.'

The animals missed their key feeding periods for two years in succession. Too hungry to hibernate, they became exposed to the harsh cold - and resulting diseases.

It is the first time in the history of observations of these Asiatic bears in Russia that 'exhausted' animals have failed to hibernate, and this applies to adults and cubs.

Many died of hunger and cold, said the scientist, who is research fellow of the Institute of Water and Environmental Problems of the Far Eastern Branch of the Russian Academy of Sciences.

'On their bodies we saw the signs of skin diseases - large areas with a lack of hair, probably the result of weakened immunity and metabolic disorders.

He highlighted this shocking fact: The dead animals were emaciated. Their weight was only half the norm for black bears. 'We found many bears that died of hunger and cold in forests, and in dens,' said Dr Kolchin.