Northern Hawk Owl

The northern hawk owl (Surnia ulula) is a medium-sized owl of the boreal forest, immediately distinctive because of its long tail, relatively small head and upright posture. Adults are about 36–45 cm long, have a wingspan of roughly 69–82 cm and weigh around 300–380 g. The upperparts are dark brown with white spotting, while the pale underparts carry narrow dark bars.

Its shape and behaviour can look surprisingly hawk-like. The wings are pointed for an owl, the flight is fast and direct, and birds often perch conspicuously on the very top of a spruce, dead tree or utility pole while scanning the ground. The yellow eyes and pale facial disc remain unmistakably owl-like.

Northern hawk owls favour open boreal forest rather than dense continuous woodland. Typical habitat includes conifer and mixed forest broken by bogs, burns, clearcuts and other openings. Tall isolated trees are useful as lookout posts, while old trees with cavities are important for nesting.

Forest disturbance is not always negative for this species. Clearings and young regenerating forest can support high numbers of small mammals and make them easier to detect from a perch, provided suitable cavity trees remain nearby. Landscapes that combine open feeding habitat with older cavity-bearing trees provide both hunting and nesting opportunities.

The northern hawk owl is a small-mammal specialist. Voles and lemmings dominate much of the diet, with shrews and other small mammals also taken. Birds, including thrushes, finches and occasionally larger species, become more important when rodent prey is scarce.

A study published in 1990 followed three breeding pairs in southeastern Norway and found a rapid dietary shift as the snow melted. While the ground was fully snow-covered, smaller bank voles from mature forest dominated the prey. As snow-free patches appeared on clearcuts, larger field and root voles became much more important. The study showed that the owl responds not only to how much prey is present, but also to how easily that prey can be reached beneath the snow.

Northern hawk owls hunt mainly from exposed perches. They watch the ground for small mammals before launching a fast, direct attack and may also hover briefly while searching open areas. Unlike most owls, they are strongly active by day, although hunting also occurs around dawn and dusk.

Field experiments in southeastern Norway, published in 1992, showed that higher perches allow longer horizontal attacks and longer moves between successive lookouts. A hawk owl can therefore balance the time spent scanning one patch against the distance covered when it shifts to a new perch, making perch height and spacing an important part of its hunting efficiency.

The northern hawk owl is highly nomadic rather than a regular seasonal migrant. When vole populations collapse in one region, birds may leave in large numbers and appear far to the south in irregular irruptions. A study published in 2023 found that such movements in Fennoscandia are influenced both by poor rodent conditions in the areas birds leave and by good feeding conditions farther south.

Southern Norway can receive very large influxes in such years. Autumn 2016 was an extreme example; a study published in 2017 estimated that roughly 10,000–20,000 hawk owls were present in southern Norway during the irruption.

Northern hawk owls nest in cavities rather than building a nest of their own. Natural hollows, broken tree trunks, old woodpecker holes and nest boxes can all be used. Clutches range from three to 13 eggs and are often largest in years when voles are abundant. The female incubates for about 25–30 days while the male supplies food.

She is particularly defensive around the nest and young. After hatching, the female initially stays close to the chicks and distributes prey brought by the male; later both adults contribute more directly to feeding. Young leave the cavity after about 23–27 days, before they are fully independent, and spend a period climbing and perching around the nest area while the adults continue to feed and defend them.

The northern hawk owl is classified as least concern on the IUCN Red List. Its very large boreal range and naturally fluctuating numbers make short-term changes difficult to interpret because local abundance can rise dramatically after good rodent years and fall again just as quickly.

Forestry can both create and remove habitat. Clearcuts and regenerating forest may improve hunting conditions, while the removal of old cavity-bearing trees can reduce nesting opportunities. A varied boreal landscape with both open feeding areas and mature cavity trees therefore provides the species with both hunting and breeding habitat.