Asio flammeus (Pontoppidan, 1763)
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Basis for Listing
The short-eared owl is distributed nearly worldwide, occurring on every continent except Australia. In North America, this species ranges from the Arctic tundra south to the mid-United States. Concern regarding its status in the United States has been raised in several parts of its range, particularly in the northern and eastern regions. It has been on the National Audubon Society's Blue List since 1976. The short-eared owl was once a common and widespread summer resident in Minnesota. Although little is known of its exact breeding range, the species occurred widely during the first half of this century and was frequently observed throughout the state, except in the northeastern and southeastern regions.
The short-eared owl is a medium-sized, buffy-brown owl with long wings. Unlike most other owls, this species is most often seen flying low over open grasslands during the day, especially at dawn and dusk. In flight, short-eared owls are best identified by the dark wrist marks and black wing tips on the undersurface of the wings. The uppersurface of the wings have a buff-colored patch near the base of the primaries. The species' distinctive flight pattern is bouncy, agile, and rather moth-like. Diurnal activity and lighter plumage, with more prominent wing markings, distinguish this species from the long-eared owl (Asio otus) (Holt and Leasure 1993). The short-eared owl is unique among Minnesota birds in that it is one of only a few species in which the female is more brightly colored than the male.
Short-eared owls are found in open habitats such as native prairie, pasture, Conservation Reserve Program grasslands, sedge wetlands, shrub swamps, and open peatlands. They are most often found in extensive tracts of habitat, rather than small, isolated patches, particularly during the breeding season. In the winter and during migration, short-eared owls will use a variety of open country habitats.
Biology / Life History
Banding data show seasonal migrations of the short-eared owl, especially in the northern part of its range. A nomadic species, the short-eared owl responds to fluctuating small mammal populations, and is particularly responsive to vole and lemming populations. Because the short-eared owl moves in response to its food supply, it may remain to breed in atypical breeding habitat if small mammals are abundant (Clark 1975; Holt and Leasure 1993). The species feeds mainly on voles in North America. Other small mammals and some birds are also taken. The short-eared owl hunts both day and night, although winter hunting may occur primarily at dawn and dusk. It hunts while flying, and uses both auditory and visual cues in detecting prey. When prey is located, the bird may hover before striking (Holt and Leasure 1993). Short-eared owls are seasonally monogamous or polygamous. During the mating season, males vocalize with a Voo-hoo-hoo-hoo-hoo song, or a variety of tooting calls. Both adults typically defend the nest vigorously by barking, screaming, or enacting distraction displays. Short-eared owls are ground nesters. The female chooses a dry site, scrapes out a bowl-like area, and lines it with grasses and feathers. Eggs are cream-colored and incubated only by the female. Upon hatching, young are semi-altricial and able to walk out of the nest after 12-18 days. They can fly after 24-36 days (Holt and Leasure 1993). Short-eared owls roost and sleep mainly on the ground. During fall and winter, they may gather in communal tree roosts, frequently with long-eared owls (Holt and Leasure 1993).
Conservation / Management
Breeding bird surveys from 1966-2001 indicate a 3.5% annual decline over this bird's range, with more serious losses (11.4%) in Canada (National Audubon Society 2003). Habitat loss and degradation, including conversion of native open habitats to agriculture and reforestation of open lands, are the main factors affecting short-eared owl populations. Protection and management of large marshes, peatlands, and native grasslands for waterfowl and shorebirds can also benefit short-eared owl populations (Holt and Leasure 1993). Because short-eared owls nest on the ground in open areas, their eggs are highly vulnerable to mammalian predators, such as fox, raccoon (Procyon lotor), weasels (Mustela spp.), skunk, cats, and dogs (NatureServe 2008). Predator control programs that are used to benefit other ground nesting birds will also benefit this species. Avian predators, such as herring gulls (Larus argentatus) and various raptors, also pose a threat to nestlings and adults (Holt and Leasure 1993). Additionally, illegal hunting by humans has played a role in the reduction of short-eared owl populations (NatureServe 2008). Public education programs that increase awareness of the value of this and all raptors in natural and agricultural environments would benefit this species.
Conservation Efforts in Minnesota
Few intensive short-eared owl surveys have been done in Minnesota. Although the species has been recorded during the breeding season in 20 counties since the 1970s, surveys conducted by the Minnesota Biological Survey (MBS) since 1987 have found short-eared owls at scattered locations in only five counties, primarily in the far northwestern part of the state. Nesting was verified by MBS in Marshall County in 1990 and 1992. Short-eared owls have been observed in other counties, but nesting has rarely been documented. Continued breeding season inventories are needed to determine the short-eared owl's population status and to locate areas with current and potential nesting habitat. Expanded efforts to acquire, protect, and restore native grasslands, marshes, and bogs are needed to preserve the disappearing habitats this species depends on.
Clark, R. J. 1975. A field study of the Short-eared Owl, Asio flammeus (Pontoppidan), in North America. Wildlife Monographs 47:1-67.
Holt, D. W., and S. M. Leasure. 1993. Short-eared Owl (Asio flammeus). Number 61 in A. Poole and F. Gill, editors. The birds of North America. The Birds of North America, Inc., Philadelphia, Pennsylvania.
National Audubon Society [Audubon]. 2003. Audubon Watchlist: Short-eared Owl. Audubon home page. <http://www.audubon.org>. Accessed June 2003.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. <http://www.natureserve.org/explorer>. Accessed 3 June 2008.