Montana Field Guide

Boreal Owl - Aegolius funereus

Round-headed, although head appears rectangular. Eyes yellow, bill yellow/white. Facial disk white, surrounded by distinct black trim. Forehead spotted. Ventrally, white with brown vertical streaks along chest, sides, and flanks. Dorsally, brown with large conspicuous white spots. Juveniles have a dark brown/black facial disk, white forehead, and are light chocolate brown throughout the upper chest, grading into light brown on the belly. By early winter, juveniles resemble adults in plumage. SIZE: nine to 11 inches. WEIGHT: four to six ounces. VOICE: "To, to, to, to¿," given rapidly and varying in number. Voice is similar to common snipe.

Saw-whet owl is smaller, bill is black, has reddish/brown on the facial disk, and ventral streaking.

Montana Range

Resident and migratory, with some elevational migration (FWP). In Idaho, owls tended to use higher elevations during summer, but overlap between seasons was complete (Hayward 1989). Owls dispersed in years of poor prey concentration in Idaho, and the more northerly populations were more nomadic (Hayward and Verner 1994).

High elevation spruce/fir forest, with lodgepole pine sometimes present (FWP). Mature spruce/fir forests with multilayered canopies and a highly complex structure, at elevations greater than 1500m with a mosaic of openings or meadows (Hayward 1989). In central Idaho, owls nested in mixed conifer (40%), spruce-fir (18%) Douglas-fir (21%) and aspen stands (21%) (Hayward 1989). One nest in MT was found in a dead broken-topped subalpine fir; nest opening measured 73X64 mm (Holt and Ermatinger 1989). Nests in MT have been exclusively lodgepole pine and spruce fir; no owls were found below 1292m in MT/ID (75% occurred >1584m) (Hayward and Verner 1994).

Predominately small mammals, with a few birds and insects (FWP). The red-backed vole is the main prey species in ID and CO. Other vole species taken when available along with other small rodents, birds, and insects (Palmer and Ryder 1984, Hayward 1989). Small mammals constitute 79% of their prey (Hayward and Verner 1994).

Boreal owls roost at sites scattered throughout their home range, rarely in the same stand on consecutive nights or the same tree more than 2X per year; they selected cool micro-sites in summer (Hayward 1989). They roost alone, usually far from their nest and mate. Owls use a sit-and-wait hunting method (Hayward 1989). Marten are the most important predator of owlets and adult females at the nest site; red squirrel predation upon eggs is also suspected in Idaho; large range: both winter and summer average >1000 ha (Hayward and Verner 1994). Young boreal owls frequently disperse long distances from natal sites; in Finland, median distances of 88 and 21 km between juvenile male and juvenile female banding sites were reported; 20% of recoveries for owls marked as nestlings exceed 100 km in West Germany and 51% in Finland (Hayward and Verner 1994).

Begins nesting in late March or April. Nests in woodpecker holes or possibly natural cavities. Clutch size two to six. Incubation approximately 28 days. Young fledge at approximately 30 days (FWP). Probably breeds throughout its range in Montana. One nest in MT fledged young 20-24 June (Holt and Ermatinger 1989). In Idaho, males start singing in late Jan., females in early Feb.; call rates increase through March. Egg laying takes place 12 Apr.-24 May. Fledging takes 27-32 days (Hayward 1989). Monogamous for 1 breeding season; pair bond lasts for single season and most individuals nest with new mate each year (Hayward and Verner 1994).