Appearance

Juvenal Plumage

Feathers of body and greater, median, and lesser wing coverts of very loose and downy structure especially on head and underparts. When not fully grown this plumage has general appearance of down as distal portions of rami appear as though they were separate filaments. In this stage much white nestling down still adheres to tips of rami. Upperparts, greater, lesser and median wing coverts and underparts dark mouse brown, feathers tipped and speckled grayish white, those of scapulars and mantle not of such loose structure as rest and faintly barred whitish; facial disk and chin white, feathers tipped brown; toes white; wing feathers, primary coverts and tail feathers of normal structure, white, barred brown like adult female but tips of innermost secondaries and primary coverts considerably mottled brown (Witherby et al. 1952). Flight feathers were still sheathed at the base of a 40-day-old, flightless female juvenile (1,800 g, wing chord 320 mm, tail 135 mm, culmen from cere 25 mm). Dark down predominated ventrally, but white winter feathers were starting to replace the down. Specimen shows down feathers still attached to the tips of incoming winter feathers (Parmelee et al. 1967). The juvenal body plumage, greater, lesser and median coverts are molted but often not completed before October. Remiges, rectrices and primary coverts are not molted (Witherby et al. 1952).

Basic I Plumage

First-year males with white bib of 2–8 cm present and back of head primarily white. First-year females with barring present in all areas of plumage except for white facial disk, tarsi, feet and wing linings; white bib, if present, less than 4 cm and back of head primarily barred. Females also show more rows of bars on underside (6 rows) and upperside (3 or more rows) of tail than do males (3 or less rows). Both sexes show moderate or extensive mottling on distal portions of greater and/or median secondary coverts (Josephson 1980).

Basic II Plumage

Not clearly defined. Specimens examined by Josephson (1980) showed mixed characteristics of first-year birds and adults, suggesting that second-year birds retain characteristics of the first basic plumage to a variable extent while displaying many features typical of adults. Not clearly defined. If Josephson’s (1980) suggestion proves correct concerning a basic II plumage, this molt probably takes place during the summer when birds are two years old.

Definitive Basic Plumage

Plumage of adult males entirely white or white except for narrow, sparse, pale gray, or brown barring on breast, back, wings, head and/or tail. Plumage of adult females with moderate to extensive barring present on breast, wings, head, and/or tail; little if any mottling on distal portions of greater and/or median secondary coverts; white bib of less than 8 cm present and/or back of head primarily white (Josephson 1980).

The darkest males and the palest females are virtually alike in color, but the whitest birds, sometimes practically pure white, are always males, and the most heavily barred ones are always females (Bent 1938). In addition to their heavier barring, incubating females often have a highly soiled plumage, which easily identifies a breeding individual on the nesting grounds. Adults have one complete annual molt, beginning in July and lasting into early fall (Bent 1938).

Bill And Gape

Short, strong and much compressed. Upper mandible strongly curved and projecting at tip, which is sharply pointed. Lower mandible broader and shorter with rounded tip. Blackish horn colored. Nostrils covered by bristle feathers of disk (Witherby 1952).

Iris

Brilliant golden yellow, at times almost orange (Sutton 1932).

Legs And Feet

Tarsus and toes thickly covered with feathers (with long, threadlike rami). Three toes directed forward and one backward. Claws long, much compressed, strong, curved, and tapering to sharp point. Blackish horn color similar to bill (Witherby et al. 1952).

Linear

Ranks first in over-all size among the 18 species of owls in North America (Burton 1973). First-year birds and adults of the same sex do not differ significantly in wing length or in length of central rectrices, but both are significantly larger for females than for males regardless of age (Josephson 1980). Most published accounts on measurements combine age groups (Table 1.) .

Probably the best information to date relating to fat conditions and body weights derives from Kerlinger and Lein’s (1988a) study of live or freshly killed birds rather than salvaged specimens that may have lost weight due to desiccation, injury, etc. For wintering owls in Alberta, those with no fat or light fat deposits are not distributed randomly among age-sex classes. Immature males have no fat or light fat deposits more often than expected and moderate to heavy fat deposits less often. Adult females show moderate to heavy fat deposits more often than expected, and no fat or light fat deposits less often. Deviations for adult males and immature females account for less than 15% of the chi-square values

Mean weights reported by Kerlinger and Lein (1988a) are significantly greater than those based primarily on museum specimens by several other researchers. In their sample, males (n = 23) range in weight from 1,606–2,043 g (mean 1,806 ± 30), females (n = 21) 1,838–2,951 g (2,279 ± 57). Approximate minimum weights of birds with at least moderate fat deposits are estimated about 1,575 g for males and 1,950 g for females. Adults tend to be heavier and fatter than immature birds. For practical considerations relating to survival, Kerlinger and Lein recommended that the weights of captive males should exceed 1,800 g and that of females 2,200 g before being released in the wild. These are thought to be approximate mean weights for healthy birds during winter. Needed at present are many more weights of live or freshly killed specimens taken during the breeding season. One nonbreeding adult male weighed 1,630 g on 27 Jul 1962, and one breeding adult female weighed 2,025 g on 28 Aug 1960 when collected by Parmelee et al. (1967) in the Canadian Arctic.