The Ussuri brown bear (Ursus arctos lasiotus), also known as the Ezo brown bear, Russian grizzly bear, or the black grizzly bear, is a subspecies of the brown bear or a population of the Eurasian brown bear (U. a. arctos). One of the largest brown bears, a very large Ussuri brown bear may approach the Kodiak bear in size. It is not to be confused with the North American grizzly bear. Appearance It is very similar to the Kamchatka brown bear, though it has a more-elongated skull, a less-elevated forehead, somewhat-longer nasal bones and less-separated zygomatic arches, and is somewhat darker in color, with some individuals being completely black, which once led to the now-refuted speculation that black individuals were hybrids of brown bears and Asian black bears. Adult males have skulls measuring on average long and wide. They can occasionally reach greater sizes than their Kamchatkan counterparts; the largest skull measured by Sergej Ognew (1931) was only slightly smaller than that of the largest Kodiak bear (the largest subspecies of brown bears) on record at the time. Behaviour and biology Dietary habits Although the diet of an Ussuri brown bear is mainly vegetarian, being a large predator it is able to kill any prey in its habitat. In Sikhote Alin, Ussuri brown bears den mostly in burrows excavated into hillsides, though they, on rare occasions, den in rock outcroppings or build ground nests. These brown bears rarely encounter Ussuri black bears, as they den at higher elevations and on steeper slopes than the latter species. They may, on rare occasions, attack their smaller black relatives. In middle Sakhalin in spring, brown bears feed on the previous year's red bilberry, ants, and flotsam, and at the end of the season, they concentrate on the shoots and rhizomes of tall grasses. On the southern part of the island, they feed primarily on flotsam, as well as insects and maple twigs. In springtime in Sikhote Alin, they feed on acorns, Manchurian walnuts, and Korean nut pine seeds. In times of scarcity, in addition to bilberries and nuts, they feed on larvae, wood-boring ants, and lily roots. In early summer, they strip bark from white-barked fir trees and feed on the cambium and sap. They also eat berries from honeysuckle, yew, Amur grape, and buckthorn. In southern Sakhalin, their summer diet consists of currants and chokeberries. In August n the middle part of