northern hawk-owl will lay 3–11 eggs per brood. The nest sites are usually the tops of hollow stumps of old dead spruce trees. These nesting sites are usually above ground for the North American S. u. caparoch and approximately above ground for the Eurasian S. u. ulala. The specific dates of egg appearance can be quite variable depending on locality. In central Canada eggs are usually laid from 30 March to 5 June. On Newfoundland the appearance of eggs occurs later, between 9 May and 11 June. In Finland, however, eggs can be found anywhere between 30 March to 23 June. For the most part, the female northern hawk-owl does the incubating of the eggs, whilst the male forages for food. Once the chicks have hatched their roles shift drastically. At about two weeks into the chicks' lives, the female starts to leave the nest for long spans of time (5 hours or more). This span of time is presumably when the female hunts. The male, however, will guard the nest diligently until the chicks leave. When predators (usually other raptors) fly nearby, the male will sometimes chase them away from the nest if he feels it is necessary. Once the owlets have grown to a size which allows less parental supervision, they will leave the nest. This occurs on average after their 21st day, and can begin as early as mid-June. After this the female will provide most of the care. However, the male will remain close and will still feed his young on occasion. The northern hawk-owl has also been known to nest on cliffsides. It has little fear of humans, and will attack if the young are approached too closely. Food and feeding The northern hawk-owl feeds on a variety of prey, which can include small rodents to mammals more robust in size, and a variety of birds — a typical diet for many boreal owls. In Eurasia the northern hawk-owl is known to feed primarily on voles from the Microtus family. These voles usually follow a 3–4 year cycle of abundance. Therefore, S. u. ulula numbers are affected negatively when the numbers of voles are lowest. In North America the subspecies S. u. caparoch also feeds upon microtine voles, but its population is primarily based on the ten-year cycling of the snowshoe hare (Lepus americanus). In Eurasia the northern hawk-owl's biomass consists of about 94% microtine