Aegolius funereus There are two northern species of the small round-headed owls in the genus Aegolius, the Boreal Owl and the Northern Saw-whet Owl. Both are forest birds that are often hard to find, primarily because they are strictly nocturnal in their activities and spend most of their daylight hours snuggled up against the trunk of conifers. Occasionally, jays or chickadees will alert a passerby to the presence of a roosting owl by mobbing it and thus relaying its location. Many owls avoid competition with diurnal predators, such as hawks, by feeding primarily at night. The auditory hunting of owls is effective only in a quiet environment.

The Boreal Owl, Interior Alaska’s smallest owl, fills the niche in the Denali area that it’s more southern Alaskan counterpart, the Northern Saw-wet Owl plays. Boreal Owls (Tengmalm’s owl in the Old World) occupy boreal and subalpine forests across the circumpolar world. They are nomadic throughout their range and are generally year-round residents, although, they may disperse, particularly the females, in years when food resources are scarce. Prey abundance, particularly red backed voles and mice influence the number of Boreal Owls in the Denali area. These little predators can capture prey hidden under snow or under dense vegetation because their ears are adapted for precise location of sounds. These owls will cache food in crevices or tree forks and then will assume the incubating posture to thaw the frozen prey.

Beginning in late March through early May the male owls are singing in hopes of finding a mate and declaring their territory. Their soft song allows the owl to be heard more often than seen but it greatly helps to determine a nesting area. They are obligate cavity nesters and often use cavities made by woodpeckers for nesting. In owls, the pair bond is usually monogamous but in the Boreal and Northern Saw-whet Owls polygyny is found. Boreal Owls show the most extreme reverse sexual size dimorphism of any North American owl with the females being much larger than males. In courtship and during incubation the male feeds the female and will bring food to the female to feed the young after hatching.

Many cavity-nesting owls have declined in numbers after logging operations remove their nest sites. Luckily, Boreal Owls will use artificial nest boxes and this has resulted in rebounds of their numbers, especially in rejuvenating forests where natural cavities are not yet available. Chemicals meant for other organisms, such as insecticides, toxic mammal baits and herbicides cause abnormal eggs, small clutches and poor fledging success. Both the direct effect of these chemicals accumulating in owls at the top of the food chain and the indirect effect of decreased prey availability contribute to owl population declines. Luckily, the Denali area has yet to be threatened with urban sprawl and agriculture which has decimated much of the lower 48 habitat for owls and many other bird species. It is our one and only migrating species of owl, the Short-eared Owl, which nests in Denali that is listed on the WatchList because of steep population declines. Threats associated with the disappearance of grassland habitats on its winter range create dire concern for this species. (Snowy Owls migrate through the Denali area, coming and going to their Arctic nesting grounds but do not nest in Denali.)

So, on a beautiful March evening in Denali, take a walk in the woods and listen for the soft song of the Boreal Owl, it is a true sign that spring is on its way.