Northern Hawk Owl (Surnia ulula)
The northern hawk owl occupies a circumpolar range and breeds in Alaska, northern Canada, Scandinavia, and across northern Russia. Three subspecies exist worldwide but only one, Surnia ulula caparoch, resides in North America. These owls live and breed in the northern boreal forests of Alaska, Canada, and Newfoundland.
Largely nomadic, northern hawk owls move across their range in response to prey availability and climatic conditions. When the weather is severe and prey availability is low, northern hawk owls may move southward towards the more temperate latitudes of Alaska, Canada and the northern continental United States. These southern movements are referred to as "irruptions" and may span thousands of miles.
Population densities of northern hawk owls are low throughout interior Alaska. When prey is plentiful, they will remain year-round in Denali and surrounding areas. However, during times of food scarcity, many will leave to find richer hunting grounds. In their never-ending drive for sustenance, northern hawk owls cover vast areas in search of food.
Northern hawk owls are skilled predators. They use hunting techniques very similar to hawks and small falcons. Active mostly by day, they primarily hunt from high perches bordering open habitats. They can be seen targeting their prey with a visible "pounce-like" posture just before swooping in for the kill. In the winter, they have been observed finding and catching prey hidden up to a foot under the snow surface. Additional hunting techniques include hovering, capturing prey in flight, low contour flying, soaring, and ground pursuit. These behavioral traits paired with a hawk-like appearance are why this owl is called the hawk owl.
In Denali northern hawk owls eat voles, shrews, lemmings, snowshoe hare, squirrels, weasels, grouse, ptarmigan, and various small birds. Snowshoe hare seems to be of greater importance as a prey item to northern hawk owls in Denali than to those in other regions such as Scandinavia.
Northern hawk owls must remain wary of natural predators such as the northern goshawk, great horned owl, golden eagle, gyrfalcon, peregrine falcon, and lynx. In addition, marten and weasel are known to prey on eggs and nestlings.
The breeding season for northern hawk owls in interior Alaska begins as early as March. The male establishes a nest territory and attracts a mate by calling and displaying during flight. When a female shows interest in the male, the pair nurtures the growing bond with mutual vocalizations, bill rubs (a behavior known as billing), and displays. Just before mating, the male caches food in and around the nest and brings prey to the female. Like many other northern owls, hawk owls may not lay eggs if prey abundance is low.
Most northern hawk owl nests are found in the hollow tops of broken trees or in tree cavities. Research suggests that yearly reuse of nests is not common, but some northern hawk owls are known to use the same nest sites year after year. Northern hawk owls also show fidelity to certain nesting areas and may use nest sites within a particular area for many years. For instance, Adolph Murie recorded northern hawk owls nesting in Igloo Forest in Denali in the 1930's. Over 90 years later, researcher John Shook also found northern hawk owls nesting in Igloo forest in Denali.
In Alaska, northern hawk owls lay clutches of 3 to 7 eggs in April and early May. The female incubates the eggs for 25 to 30 days and broods the young for an additional 10 to 14 days after hatching. During incubation and brooding, the male is the primary hunter and delivers food to the female.
In Alaska, young northern hawk owls leave the nest approximately three weeks after hatching. At this stage of life they cannot fly long distances, but they can walk, climb, hop, and fly horizontally in short bursts. Over the next 3 to 5 weeks the developing fledglings remain near the nest site and are fed and protected by their parents until they reach independence approximately 2 1/2 to 3 months after hatching.
It is believed that northern hawk owls may begin breeding at 1 year of age.
The life span of northern hawk owls is approximately 10 years.
Many birders are drawn to Denali hoping to see this strikingly beautiful species. Plumage of both sexes is dark brownish-black with white streaks and spots on the head, back, and wings. The underside is white with dark barring from the chest to the tip of the tail and the legs are feathered to the talons. Small golden eyes and a yellow bill sit at the center of a gray face that is bordered with dark brown.
Medium-sized for an owl, northern hawk owls have compact (wing-chord < 9 inches) pointed wings and a long tail. Males average 14 to 16.5 inches (36 to 42 centimeters) in length and weigh approximately 10.5 ounces (300 grams). Females are slightly larger measuring 14.5 to 17 inches (37 to 44 centimeters) long and weighing an average of 12 ounces (340 grams).
Northern hawk owls are a rare sight in the wild. They are often spotted perched on top of spruce trees. Birders with good ears can also find them by listening for their vocalizations. In Denali and adjacent areas, birders are most likely to find northern hawk owls in late winter or early spring as they move in search of nest sites, mates, and prey. Summer viewing is also possible when owls are nesting.
Unusually tolerant to humans, northern hawk owls will often allow a person to approach quite closely. During the breeding season however, they may aggressively defend their young. Dive-bombing northern hawk owls can deliver sharp blows to the head and upper body with razor sharp talons. In Denali, birders must remain at least 300 feet (100 meters) away from nest sites during the nesting season.
While populations of northern hawk owls appear stable, increased forestry and fire suppression in northern latitudes may reduce their habitats. Northern hawk owls are also vulnerable to poaching due to their tolerant nature and penchant for exposed perches. In addition, they fall victim to accidental trapping and collisions with power lines, vehicles, and trains.
Northern hawk owls are one of the least studied birds in North America. Their low densities and tendency to nest in remote places make it very difficult to study this northern nesting owl. Research conducted in Denali in the early 1980's and at the turn of the 20th century has provided valuable information about the habitat requirements, food habits, and nesting ecology of northern hawk owls in Alaska.