Northern Pygmy-Owl Glaucidium gnoma Scientific name definitions

The Northern Pygmy-Owl is a small, gritty predator that occupies a diversity of structurally complex forests and uses a variety of prey types across its broad geographic range. Its habits and life history strategy differ markedly from other forest owls. It is active by day, not at night. In flight, its rapid wingbeats are more akin to a large sparrow or a shrike than to the soft, pulsing flights and fixed-wing gliding attacks that are common among other owls. Even its body is different, with its ears symmetrically arranged and its nape plumed with false eyespots that may deter unseen attacks from the rear. When hunting it uses its small stature, stealthy flights, and cryptic coloration to stalk small birds in the forest canopy, and employs a patient, stop-and-go strategy to pounce on small mammals, birds, lizards, and insects in the understory.

The life-history strategy of the Northern Pygmy-Owl is, in some ways, similar to cavity-nesting passerines. Pygmy-owls appear to be short-lived, and as such are devoted to maximizing their reproduction by (1) nesting annually, (2) nesting early in the season and producing larger broods in years of high prey abundance, (3) renesting after the loss of a clutch or mate in the early breeding season, (4) rearing nestlings alone after mate loss later in the season, (5) nesting disproportionately in tree species where they achieve the greatest productivity, and (6) achieving high rates of nest success associated with cavity-nesting. Furthermore, like other small, diurnal birds they are secretive at their nests, using stealthy behaviors and cryptic vocalizations to conceal the location of eggs, nestlings, and recently fledged young.

The male Northern Pygmy-Owl is alternatingly bold and surreptitious, often starting the day at the top of the tallest tree to broadcast his penetrating, monotonal song, before transitioning into a tiny forest ninja that moves clandestinely through the canopy and understory to strike unwary prey. In contrast, the female is ghost-like and seldom seen or heard during the day. In the nesting season, the male is a tireless hunter and the female is devoted to offspring, staying inside the nest cavity for nearly six weeks, taking breaks only to receive food from the male and expel waste. To communicate with her mate or young, she uses a soft, squirrel-like chittering call that is presumably more likely to be overlooked by mobbing songbirds and predatory raptors. When a female loses her mate early in the breeding season, she will move into the surrounding landscape, visiting territorial males until she finds an available mate. When a male loses his mate, he will sing from the canopy of his territory for hours each day, sometimes for weeks on end, to attract a female and renest before the breeding period is over. But if owlets are already in the nest, the single adult will attempt to raise them alone, accepting all the duties of parental care, nest defense, and hunting.

As a small, diurnal forest species, the Northern Pygmy-Owl is vulnerable to attack from hawks, larger owls, and mammalian and reptilian nest predators. Its vulnerability is evident in the narrow, concealment posture it assumes when a hawk soars overhead or perches nearby. Females are particularly at risk. While laying, they are gravid, plump, and slow from over-eating, and are at risk of avian predators. While incubating and brooding young their feathers become worn and broken, and they must maintain vigilance against predators like ermine that can climb trees and kill them in the nest cavity. Thus, after her young have departed the nest, it is the female that takes leave of her family group first to replenish herself, sometimes weeks before offspring independence and natal dispersal.

The range of the Northern Pygmy-Owl is broad and closely overlays the mountain ranges of western North America. At its northern range limit in the Yukon and northern Alberta, it occupies areas away from the mountains in the transitional zone of boreal forests and aspen parklands. Along the western extent of its range, it occurs in the dense, moist, coast range forests of southeastern Alaska and British Columbia south to California, and in pine-oak forests along the rugged coasts of Baja California, Mexico. The eastern border of its range follows the forests and dry woodlands of the Rocky Mountain foothills from Alberta and Montana south to New Mexico. The range extends southward into the Madrean pine-oak forests and woodlands of the Sierra Madre of Mexico. At its southern range limit, it inhabits subtropical highlands, primarily in Guatemala and Honduras. Across its range, the Northern Pygmy-Owl inhabits a wide variety of forest types, but is most consistently found in sloped terrain with structurally-complex, older forest stands — including old-growth forest — with snags and nest cavities for breeding. The habitat often contains coniferous trees and typically has ample vegetative structure to support their primary prey, small birds and small mammals, though the forest understory in some regions may be fairly open, with relatively little ground cover.

Across its range, the voice, body size, diet, and ecology of the Northern Pygmy-Owl vary to such an extent that the taxonomic unity of its subspecies is questionable. In Canada and most of the United States, the male’s song is a penetrating series of monotonous single notes, but even here there is variation. In the dense, coast forests, from Alaska and British Columbia to southern California, and in the mountain ranges of Alberta, Montana, Idaho, and northern Wyoming, notes of the song are usually separated by a 2 to 4 second interval. Pygmy-owls in this region are moderately large and feed primarily on small birds and mammals. But in drier, more open woodlands, from Utah and Colorado south into Arizona and New Mexico, their song is faster (intervals between notes only about 1 second), body size is slightly larger, and pygmy-owls appear to feed more frequently on reptiles. Southward, in the Madrean pine-oak woodlands of northern and central Mexico, the song becomes irregular, often a mix of singled and doubled toots, and body size is somewhat smaller than in the north. In Guatemala and Honduras, habitat use changes to highland forest and the voice is a rapid song that includes triple-toots. Owing to these regional differences, speculation abounds that the Northern Pygmy-Owl subspecies complex might instead be a combination of several distinct species, but insufficient evidence has been presented to support such claims.

In 1888, the ornithologist Charles Bendire proclaimed that "the habits of the Northern Pygmy-Owl are by this time pretty well-known and there remains little for me to add to its life history that is really new" (1 Bendire, C. E. (1888). Notes on the habits, nests and eggs of the genus Glaucidium Boie. Auk 5:366–372. Close ). Wrong as he was, for the next 100 years almost no quantitative research was conducted into the species' ecology. But more recently, research on the Northern Pygmy-Owl has increased, and the picture of its once poorly documented ecology is gradually coming into focus. Investigations have been made into the species' nesting ecology (2 Deshler J. F. (2010). Nest-site habitat selection and breeding biology of the Northern Pygmy-Owl in northwestern Oregon. M.S. thesis. Portland State University, Portland, OR, USA. Close , 3 Deshler, J. F. (2021). Northern Pygmy-Owl (Glaucidium gnoma) nesting ecology in northwestern Oregon. Wilson Journal of Ornithology 132:352–365. Close ), habitat use (4 Giese, A. R., and E. D. Forsman (2003). Breeding season habitat use and ecology of male Northern Pygmy-Owls. Journal of Raptor Research 37(2):117–124. Close , 5 Sater, D. M., E. D. Forsman, F. L. Ramsey, and E. M. Glenn (2006). Distribution and habitat associations of Northern Pygmy-Owls in Oregon. Journal of Raptor Research 40(2):89–97. Close , 2 Deshler J. F. (2010). Nest-site habitat selection and breeding biology of the Northern Pygmy-Owl in northwestern Oregon. M.S. thesis. Portland State University, Portland, OR, USA. Close , 6 Jageman, H. R. (2014). Space use, habitat selection, genetic variation, and post-fledging ecology of Northern Pygmy-Owls (Glaucidium gnoma) in northern Idaho. Ph.D. dissertation, Unversity of Idaho, Moscow, ID, USA. Close , 7 Jageman, H. R., G. G. Frye, and E. O. Garton (2018). Habitat selection by Northern Pygmy-Owls in the Rocky Mountains. Journal of Raptor Research 52(3):349–360. Close ), home-range size (4 Giese, A. R., and E. D. Forsman (2003). Breeding season habitat use and ecology of male Northern Pygmy-Owls. Journal of Raptor Research 37(2):117–124. Close , 6 Jageman, H. R. (2014). Space use, habitat selection, genetic variation, and post-fledging ecology of Northern Pygmy-Owls (Glaucidium gnoma) in northern Idaho. Ph.D. dissertation, Unversity of Idaho, Moscow, ID, USA. Close ), diet (8 Holt, D.W., and L. A. Leroux (1996). Diets of Northern Pygmy-Owls and Northern Saw-whet Owls in west-central Montana. Wilson Bulletin 108(1):123–128. Close , 4 Giese, A. R., and E. D. Forsman (2003). Breeding season habitat use and ecology of male Northern Pygmy-Owls. Journal of Raptor Research 37(2):117–124. Close , 9 Deshler, J. F., E. D. Forsman, and J. K. Swingle (2019). Diurnal activity pattern of a pair of breeding Northern Pygmy-Owls. Northwestern Naturalist 100:176–185. Close , 3 Deshler, J. F. (2021). Northern Pygmy-Owl (Glaucidium gnoma) nesting ecology in northwestern Oregon. Wilson Journal of Ornithology 132:352–365. Close ), post-fledging ecology (10 Frye, G. G., and H. R. Jageman (2012). Post-fledging ecology of Northern Pygmy-Owls in the Rocky Mountains. Wilson Journal of Ornithology 124(2):199–207. Close ), voice (11 Eisermann, K., and S. N. G. Howell (2011). Vocalizations of the Guatemalan Pygmy-Owl (Glaucidium cobanense). Journal of Raptor Research 45(4):304–314. Close ), sexual-size dimorphism (12 Earhart, C. M., and N. K. Johnson (1970). Size dimorphism and food habits of North American owls. Condor 72(3):251–264. Close , 13 Deshler, J. F. (2021). Higher reversed sexual size dimorphism among nesting pairs of Northern Pygmy-Owls (Glaucidium gnoma) in northwestern Oregon than among specimens collected at the range-wide scale. Wilson Journal of Ornithology 132:619–627. Close ), and daily activity pattern (9 Deshler, J. F., E. D. Forsman, and J. K. Swingle (2019). Diurnal activity pattern of a pair of breeding Northern Pygmy-Owls. Northwestern Naturalist 100:176–185. Close ). In one study, patterns of annual and seasonal variation in the timing and magnitude of reproduction in relation to diet have been uncovered (3 Deshler, J. F. (2021). Northern Pygmy-Owl (Glaucidium gnoma) nesting ecology in northwestern Oregon. Wilson Journal of Ornithology 132:352–365. Close ). However, much additional research is needed to fully understand the ecology of this species across its broad geographic range, and indeed, whether it is only one species, or several.

Note: Within this species account, three often cited study areas will, for consistency and brevity, be referred to as (1) the "Forest Park study area" that lies in the Tualatin Mountains, a spur of the Northern Oregon Coast Range (2 Deshler J. F. (2010). Nest-site habitat selection and breeding biology of the Northern Pygmy-Owl in northwestern Oregon. M.S. thesis. Portland State University, Portland, OR, USA. Close , 14 Deshler, J. F., and M. T. Murphy (2012). The breeding biology of the Northern Pygmy-Owl: do the smallest of the small have an advantage? Condor 114(2):314–322. Close , 9 Deshler, J. F., E. D. Forsman, and J. K. Swingle (2019). Diurnal activity pattern of a pair of breeding Northern Pygmy-Owls. Northwestern Naturalist 100:176–185. Close , 3 Deshler, J. F. (2021). Northern Pygmy-Owl (Glaucidium gnoma) nesting ecology in northwestern Oregon. Wilson Journal of Ornithology 132:352–365. Close , 13 Deshler, J. F. (2021). Higher reversed sexual size dimorphism among nesting pairs of Northern Pygmy-Owls (Glaucidium gnoma) in northwestern Oregon than among specimens collected at the range-wide scale. Wilson Journal of Ornithology 132:619–627. Close ), (2) the "Olympic Peninsula study area" of the northwest corner of the Olympic Mountain Range in western Washington (15 Giese, A. R. (1999). Habitat selection by Northern Pygmy-Owls on the Olympic Peninsula, WA. M.S. thesis, Oregon State University, Corvallis, OR, USA. Close , 4 Giese, A. R., and E. D. Forsman (2003). Breeding season habitat use and ecology of male Northern Pygmy-Owls. Journal of Raptor Research 37(2):117–124. Close ), and (3) the "Idaho and Montana study areas" of the Rocky Mountain foothills in north-central Idaho, and the western front of the Rocky Mountains in the Lewis and Clark National Forest in northern Montana (6 Jageman, H. R. (2014). Space use, habitat selection, genetic variation, and post-fledging ecology of Northern Pygmy-Owls (Glaucidium gnoma) in northern Idaho. Ph.D. dissertation, Unversity of Idaho, Moscow, ID, USA. Close , 10 Frye, G. G., and H. R. Jageman (2012). Post-fledging ecology of Northern Pygmy-Owls in the Rocky Mountains. Wilson Journal of Ornithology 124(2):199–207. Close , 7 Jageman, H. R., G. G. Frye, and E. O. Garton (2018). Habitat selection by Northern Pygmy-Owls in the Rocky Mountains. Journal of Raptor Research 52(3):349–360. Close ).