The grizzly bear (Ursus arctos horribilis), also known as the North American brown bear or simply grizzly, is a population or subspecies of the brown bear inhabiting North America. Grizzlies are considered more aggressive compared to black bears when defending themselves and their offspring. Unlike the smaller black bears, adult grizzlies do not climb trees well and respond to danger by standing their ground and warding off their attackers. Mothers defending cubs are the most prone to attacking and are responsible for 70% of humans killed by grizzlies.

Source: Wikipedia