voles, whereas in North America the percentage of biomass contributed by voles can be as low as 20%. Juvenile hares are considerably more important at 40–50%. Other animals that are important prey items for the northern hawk-owl include the red squirrel (Sciurus vulgaris) which has been documented to contribute as much as 20% to the hawk-owl's biomass. A long list of others includes mice, rats, voles, lemmings, the short-tail weasel (Mustela erminea), partridge, spruce grouse (Falcipennis canadensis), doves, pileated woodpeckers (Dryocopus pileatus), sparrows, jays, robins, starlings, buntings, grackles, and finches. In the winter, feeding strategies change: where in summer the main source of food is mammals, in the winter a bigger portion of the hawk-owl's biomass consists of ground-dwelling birds, such as the ptarmigan and the grouse. The northern hawk-owl is a partially diurnal hunter, although it has been recorded hunting at varying times and does not appear to have a preferred hunting time. Whether the bird resides in Eurasia or North America, the strategy is usually similar. The northern hawk-owl will perch and scour the immediate area for prey. As these owls are considered a search-oriented species, they likely do not stay put for long if the site is not producing prey. The hawk-owl prefers open, forest-type environments when perching. These environments include sphagnum bogs and partially deforested areas. The preferred perching tree of the northern hawk-owl is the spruce tree. When the hawk-owl attacks, it goes from a horizontal posture into a gliding dive. If the prey is further away, the bird will flap its wings a few times during the dive to increase distance. The hawk-owl has exceptional hearing and can plunge into snow to capture rodents below the surface. The type of prey the hawk-owl catches will determine its eating strategy. For mammalian prey the ritual is generally the same: the northern hawk-owl will eviscerate its prey, eat the head first (especially for prey like the red squirrel, whose head is fairly large), and then — when tackling larger prey — it will eat the organs and cache the remains; with smaller prey, the owl will simply swallow the body whole. Conservation and status Due to its low density occurrence, sporadic fluctuations, and remote breeding locations, the northern hawk-owl is one of the least studied and poorly understood birds in North America. As a result, it is almost impossible to properly estimate its numbers. In Yukon,