1901 , when Siberian weasels were introduced to Hokkaido , the Japanese night heron has also faced both competition and predation from Siberian weasels .
Which are active hunters of the fish and insects that the heron preys on .
Since 1901 , when Siberian weasels were introduced to Hokkaido , the Japanese night heron has also faced both competition and predation from Siberian weasels , which are active hunters of the fish and insects that the heron preys on .