The Short-eared Owl (Asio flammeus) is a highly nomadic species that occurs throughout much of the world. This owl responds irruptively, on a broad geographic scale to high concentrations of small mammals. Consequently, the migrations and population status of the Short-eared Owl in North America are poorly understood. Populations have declined dramatically in the northeastern U.S. and there is evidence of significant long-term declines elsewhere. Concern over population declines and a lack of information on this species in Alberta have led to its inclusion on the 'Blue List' of species that may be at risk in the province.
The Short-eared Owl is typically associated with open areas that support cyclic small mammal populations, such as voles or lemmings. Habitats used throughout the circumpolar range of this species include arctic tundra, clear-cuts, peat lands, fresh and saltwater marshes, grasslands, cropland, and shrub-steppe. In Alberta, the Short-eared Owl is most often reported in the Grassland and Aspen Parkland Natural Regions.
The Short-eared Owl is one of the few species of North American owls that routinely nest on the ground. There is a definite tendency for the species to build nests on drier ground locations, especially relative to sites used by Northern Harriers.
The irruptive nesting habit of the Short-eared Owl complicates assessment of available breeding habitat in Alberta. Prey availability is usually the proximate factor that determines breeding locales. For example, the extensive mixed-grass prairie region of the Special Areas in southeastern Alberta appears to be suitable habitat for nesting Short-eared Owls.
Winter roosts provide shelter from the weather and are usually close to hunting areas. Communal winter roosts are primarily on the ground among grasses mowed to 30-40 cm. Average visual obstruction height from Short-eared Owl roosts was significantly lower than that recorded for Northern Harrier roosts.
The Short-eared Owl is so named because of the short, inconspicuous ear tufts on top of its head. The plumage varies from light brownish-orange to buffy white, with a whitish facial disk, darkly ringed eyes, and a dark wrist patch on the underwing. The specific name, flammeus, refers to the rusty or 'flame colored' plumage. Adults of both sexes are very similar, but the males are generally paler. This is a medium sized owl with males averaging 315 grams and females 378 grams.
The Short-eared Owl is considered a loosely colonial breeder. Communal winter roosts sometimes become breeding colonies in spring, likely as a facultative response to a food resource. Courtship begins in late winter when males perform 'sky dancing' displays consisting of shallow aerial stoops, wing clapping, and a courtship song. Although Short-eared Owls often overwinter in Alberta, the first spring migrants arrive during March and early April. The female scrapes out a nest bowl on the ground and lines it with grasses. Clutch size for nests in North America are 5.6 with a range of 1 - 11. Clutch size also increases significantly with latitude. Eggs are laid at one to two day intervals and are incubated by the female for 24 to 29 days. Brooding is also performed only by the female. Young Short-eared Owls develop very rapidly leaving the nest when 14 days old and wandering up to 200 m away before fledging at 28 to 35 days.
Small mammals, particularly voles, dominate the Short-eared Owl's diet in North America. The extreme peaks that vole populations exhibit also make them a very attractive resource. Several studies have documented a high correlation between Short-eared Owl abundance and peaks in vole population cycles. In northern Europe, Short-eared Owl populations respond numerically and synchronously to fluctuations in vole density.
They hunt primarily on the wing, coursing less than 3 metres above the vegetation. They also hover at higher altitudes (up to 30 metres), essentially holding their position in the wind with limited wing movement. Less frequently, Short-eared Owls hunt from perches. Most hunting is done at night, but diurnal hunting may be required when adequate prey cannot be captured at night
Reprinted from Alberta Wildlife Status Report No. 28
with permission from Alberta
Sustainable Resource Development.