Boreal Owl––A hungry winter nomad from the Interior By Kate Persons
From Unalakleet to Nome, enchanting, pint-sized boreal owls have been popping up in unexpected places. Raised black eyebrows and wide yellow eyes can give these little owls a look of surprise, the same look that likely crosses the faces of those lucky enough to spot one.
Named after the boreal forest habitat where they live, this circumpolar owl is regularly found throughout the forests of interior Alaska. Boreal owls are normally not migratory, but periodically insufficient food can force them to “irrupt” from their breeding habitat into areas beyond their normal range in search of voles—their main food.
A scarcity of voles in the interior has likely brought these hungry owls to us this winter. Voles naturally have cyclic population fluctuations. This winter vole numbers are apparently down over a widespread swath of the Alaskan and Canadian boreal forest, driving impressive numbers of hungry owls into southern Canada and across the border into the northern United States.
The winter of 2015-2016 was the last time I was aware of a boreal owl irruption in the region. Then, one of these unusual nomads in the Nome area spent January nights hunting by our bird feeder at Banner Creek, catching plentiful voles that fed on spilled seeds beneath the feeder.
Boreal owls are the smallest owls found in the region. They are only robin-sized in length, but nearly twice a robin’s weight and their large head and rotund fluffiness makes them appear much larger.
Most raptor females are larger than males of their species, and boreal owls are an extreme example of this. Females can be half heavier than males. This is the greatest size difference between the sexes seen in any North American owl. Female boreal owls are more likely than males to leave their breeding range during irruptions, so the owls we see here are often on the large side.
Boreal owls hunt from a perch, watching and listening for movements of voles, lemmings, shrews, small birds, or insects in summer. Like most owls, the feathers on their face direct the sounds of prey to the owl’s ears. Their ear openings are asymmetrical with one being lower than the other, allowing them to locate prey precisely beneath snow or leaf litter.
When they detect prey they pounce, grabbing it with their talons, killing it either with talons or a bite to the head or neck. Small prey is eaten whole. Like other raptors, boreal owls regurgitate indigestible parts such as fur and bones about once a day as pellets, which can sometimes be found beneath favorite roosting perches.
They may cache excess food in crevices and tree forks. If it freezes, the little owls will incubate the frozen meat to thaw it.
In Interior Alaska, red-backed voles are their main prey. When voles are abundant, boreal owls have larger broods and remain resident year-round. Smaller broods are produced when voles are fewer. When vole populations crash, the owls become winter nomads.
Snow conditions can also cause winter movements by making prey hard to catch. A boreal owl’s small size prevents it from crashing through deep, crusted snow, which larger owls are able to do. This make me wonder how the nomads are faring here this winter, hunting in our icy conditions.
Boreal owls are quiet except at this time of year, around the spring equinox, when males hoot rapidly to attract a mate. Usually, they form seasonal monogamous pair bonds.
They do not build their own nests. Instead, they nest in abandoned woodpecker holes or natural cavities in trees. Boreal owls will readily use man-made nest boxes, which have been used successfully in the Anchorage and Fairbanks areas.
Although boreal owls are widespread residents of Interior Alaska forests, they are inconspicuous and seldom seen. When daylength allows, they are strictly nocturnal. During the day they often roost in dense cover, where they are well camouflaged.
The hooting of a male during the breeding season or scolding calls of small birds may be the only indications of an owl nearby.
However, during irruptions when driven by hunger, the little predators may abandon their secretive ways. They may be forced to hunt during the day, and out in the open where voles and shrews are easier to see and catch, sometimes becoming tolerant of human presence and activity.
Recently boreal owls have even made themselves right at home in Nome, moving into neighborhoods to perch on shrubs and powerlines, hunting in yards and between houses.
When these food-stressed owls enter human environments, it is of course very exciting to see such an unusual and charismatic bird. But it does not always end well for the owls in our midst. They are prone to die from collisions with vehicles and windows, if not from starvation. Irruptions can seem like an unfortunate, maladaptive behavior.
However, banding studies in Minnesota show that boreal owls found dead of starvation or accidents are only a very small proportion of the irrupting population. The vast majority are able to maintain their hidden, nocturnal lives and survive a nomadic winter.
Soon our winter visitors will head back to their breeding grounds in the boreal forest, where hopefully a new crop of voles will be waiting. Be on the lookout, and savor the sight of them now because who knows when they will return?