Abstract
Asio flammeus, a medium-sized owl found in open habitats, inhabits large areas of North America. Habitat preferences, migration dynamics, and prey availability determine permanent and seasonal distribution. Where this owl is found, it is easily recognized by physical and behavioral characteristics, many of which are unique. Short-eared owls are round-headed with prominent facial disks but inconspicuous "ears" or tufts (hence the common name). The proportionally large, boomerang-shaped wings of these tawny-colored owls (along with exceptional vision and hearing) help make them formidable predators of small mammals, especially microtine rodents. The fact that they sometimes hunt during the day and the characteristic "flopping" or "moth-like" flight makes them more conspicuous than other owls and aids in field identification. Other behaviors of this species make it interesting as well; these include communal roosting (when favored prey is abundant), elaborate courtship rituals, construction of nests on the ground, ambulatory (pre-fledgling) young, and parental training. Large avian predators and mammalian ground-nest predators cause most of the natural mortality in short-eared owls; human-caused mortality of short-eared owls results from a number of direct and indirect activities. Destruction of habitat represents the most serious threat to short-eared owls and has doubtless resulted in decreased numbers across portions of this species range in North America. The conservation of short-eared owls will hinge upon limiting urbanization and destructive agricultural practices.
Introduction and Overview
The short-eared owl (Asio flammeus), an interesting and in many ways unique species, belongs to the Family Strigidae. These open-habitat owls enjoy a nearly worldwide distribution; populations are widespread in North America. The migratory habits of some of these populations complicate the distribution pattern of this species with range increasing and contracting on a seasonal basis (Sauer et al. 1995). Where they are found, short-eared owls can be identified by their medium-size, prominent facial disks, lack of conspicuous "ear" tufts, and tawny-coloration. The wings of short-eared owls also appear conspicuously long relative to the body size; black "wrist" marks visible on the underside of the wing in flight aid field identification as does the characteristic "flopping" flight. The manoeuvrability of this species in flight, supplemented by exceptional hearing and vision makes short-eared owls formidable predators of small mammals. Microtine rodents in particular represent favored, and in some areas almost exclusive, prey (Blem et al. 1993).
Short-eared owls typically inhabit open habitats with a large prey base. Favored areas include prairies, marshes, sagebrush steppe, and heathland. Large numbers of short-eared owls often migrate into these areas when prey becomes especially abundant; prey abundance directly correlates with hunting territory size (Clark 1975). Generally, short-eared owls hunt on the wing quartering across open fields and meadows or hovering above prospective areas; on rare occasions they hunt from perches (Clark 1975). Unusual for owls, this species sometimes hunts during the day. Hunting success appears high when compared with other comparably-sized birds of prey. These owls generally quickly dispatch and eat captured prey in a predictable fashion. Pellets disgorged after digestion offer important information relative to the diet of this species and are often collected by researchers at roosting sites.
Roosts of short-eared owls, almost always located in or at the edge of hunting territories, offer protection from the weather and human intrusion (Clark 1975). Short-eared owls generally select roosting sites on the ground but low-lying brush, brush-piles, and even coniferous trees are sometimes used. Large numbers of short-eared owls may occasionally use the same roost especially in areas with abundant prey.
Other interesting aspects of the behavior of short-eared owls includes their elaborate courtship display, ground nesting habit, ambulatory (pre-fledgling) young, and parental training (Clark 1975). Courtship in this species includes ritualized flight, vocalizations by both male and female, and feeding of the female by the male. Following pair bonding and mating, short-eared owls construct nests on the ground; these consists of shallow scrapes lined with vegetation. The female short-eared owl lays a modest number of eggs over a period of several days and does all the incubating and brooding (with the male providing food). Eggs hatch asynchronously at approximately 26 days. The young develop rapidly and leave the nest at approximately 13 days (they explore the immediate vicinity on foot) with fledging occurring at approximately 29 days. Young short-eared owls rely on their parents until after fledging; some behavioral evidence suggests that short-eared owls train their offspring relative to finding prey. Despite extensive parental care, young short-eared owls suffer a 50% mortality rate to fledging (Howard and Griffith 1994). Natural predators of short-eared owls primarily include larger birds of prey but ground-nest predators may also be a factor in some areas (Clark 1975). Direct and indirect human activities also adversely affect short-eared owl populations. The declines noted in some portions of this species range reflect urbanization and agricultural practices adversely affecting habitats. Future conservation measures for this species will have to address these concerns.
Taxonomy and Systematics
Short-eared owls (Asio flammeus pontoppidan) belong to the Strigidae, the most diverse of the two families comprising the Order Strigiformes. Within the Strigidae, the genus Asio contains only 7 species but nevertheless enjoys a nearly cosmopolitan distribution (Hole 1996). Asio flammeus, in particular, has an extremely large range. Within this large range, a modest number of subspecies are recognized; only the type subspecies Asio flammeus flammeus, the subject of this paper, occurs in North America (Howard and Griffith 1994). Short-eared owls appear to be closely related to Long-eared Owls (Asio otus) based both on morphology and behavior. These two species are sympatric in many areas and on occasion may even occupy the same roosting sites (Clark 1975; Basakowski 1986). Distribution and Range The Short-eared owl occurs in suitable habitat (containing an adequate prey base) on all continents except Australia and Antarctica (Howard and Griffith 1994). In addition, this species also inhabits islands and archipelagos in the North Pacific, South Pacific, North Atlantic, South Atlantic, Indian Ocean, Carribean Sea, and Mediterranean Sea (World Conservation Monitoring Centre 1997). The vagility of this species seems noteworthy especially in light of the successful colonization of Hawaii (Hawaii Natural Heritage Program 1996), the Galapagos (Interpretation International 1996) and other isolated islands. Interestingly enough, researchers classify short-eared owls as only weakly migratory in North America (Howard and Griffith, 1994). This is due to the fact that some birds move seasonally while others maintain permanent residency. In my study area, I have observed adult birds (no doubt representing several generations) occupying the same locale year-round for approximately 7 years (the disposition of fledglings produced in this area is unknown). The migratory habits of this species complicate the picture relative to both breeding range, permanent range, summer range, and winter range.
In the United States, breeding populations are found in Alaska, the Pacific Northwest, central and northern California, the Great Basin, the central and northern Great Plains, around the Great Lakes, and northeast into Maine (Clark 1975). The Canadian Birds Trend Database (1997) reports breeding populations in all Canadian provinces as well as the Yukon Territory, Northwest Territories, and on Prince Edward Island. Based on recent information from the Breeding Bird Survey, the largest breeding populations occur in the states of Utah, Idaho, Montana, and Alaska (Sauer et al. 1995; Patuxent Wildlife Research Center 1997).
The distribution of breeding birds roughly corresponds with permanently occupied range. Summer and fall migration patterns extend the range of this species (Clark 1975). In summer, some short-eared owls migrate north to take advantage of seasonally abundant prey; this has the effect of expanding the species range well into Arctic North America. Conversely, winter range reflects migration of some birds into more southerly areas (specifically to the Texas-Louisiana Gulf Coast area, southern Great Plains, and deserts of the southwestern United States and Mexico) and consequently results in contraction of the northern range (Sauer et al. 1995). Migration is generally, but not always, in a north-south direction; some migrants move between North Dakota and eastern Oregon on a seasonal basis (Howard and Griffith 1994). The changes noted in distribution of this species probably reflect depletion of prey rather than adverse climatic conditions.
General Physical Characteristics
Asio flammeus is a medium-sized, round-headed owl 13 to 17 inches in size which weighs 11 to 14 ounces (Holt et al. 1990). Short-eared owls are named for the small and inconspicuous tufts located between and above their circular facial disks (and bright yellow eyes). The facial disks, colored grayish-white with black orbits, lie slightly above and on both sides of a black bill. Body coloration over other parts of the body is variable but most individuals are tawny-brown with heavily-streaked or "flamed" feathers - hence the specific name flammeus. As in other species of owls, Asio flammeus possesses a zygodactyl foot arrangement and feathered legs which are light-colored (buff or ochraceous). The ventral surface of the body and the underside of most of the wing are also comparatively light in color. The wings themselves are long and conspicuous relative to body size (average size 3.5 feet) and roughly boomerang-shaped; black "wrist" marks show on the underside of the wing in flight (Sauer et al. 1995). Although sexes have similar plumage in this species, Clark (1975) reported that males tend to have lighter, almost white, under-wing feathers in contrast to the analogous buff-colored feathers of females. Additional information also suggests that females may be slightly larger than males (Doan 1997). Juvenile short-eared owls, while similar to their parents, have darker plumage (Pearson et al. 1936); in particular, they typically exhibit more black on the facial disk than do adult birds (Holt et al. 1990). The cryptic coloration of both juvenile and adult short-eared owls provides concealment from predator and prey alike. I can personally attest to the excellent camouflage that this plumage provides. In my study area located near Oregon Coulee in Park County, Wyoming (N2-S2 Section 5-T51N-R99W), I have never observed a "perched" owl despite numerous trips and careful searching. The plumage of this owl, like many other members of the Strigiformes, also exhibits important adaptations for silent flight (Madson 1996). Most notably, short-eared owls have primary feathers with downy soft fringes around the outer leading edges (formed by the lack of barbules) and a slight pile over the broad surface of each individual flight feather. These adaptations not only allow silent gliding toward prey but also probably improve the owl's listening ability (due to decreased flight noise).
A number of features help short-eared owls find prey by sound. This species has prominent facial disks, moveable ear flaps in front of ear openings, and asymmetrically placed ears which occupy different vertical positions on the sides of the head (Doan 1997; Madson 1996). Facial disks function in sound collection as do the movable ear flaps; the flaps serve as sound baffles allowing owls to home in on noises originating either fore or aft. Ears asymmetrically placed on the side of the skull also help fine-tune sound reception. The slight difference in sound arrival time between the two ears helps short-eared owls pinpoint sounds. In addition to these important auditory adaptations, Asio flammeus also possesses the exceptional vision typical of most owls. Owls have large binocular eyes with powerful lenses and retinas made up of an abundance of rods (Madson 1996). The pupils of an owl's eye can expand to remarkable sizes and thus can collect light even on the darkest night. The lens (and cornea) serve to focus this light on the retina which contains a preponderance of rods in owls. This large number of rods (retinal cells or receptors important in black and white detection) translates into excellent night vision. Short-eared owls, despite their occasional daytime hunting, possess the general blueprint of nocturnal members of the Strigiformes.
General Behavioral Characteristics Niche and Diet
Short-eared owls specialize in capturing small rodents. Field observations and analyses of pellets indicate a strong dietary link between short-eared owls and microtine rodents (Snyder and Hope 1938; Short and Drew 1962; Clark 1975; Blem et al. 1993). A recent study in northwestern Montana indicated that voles (Microtus montanus and Microtus pennsylvanicus) comprised more than 95% of the diet of short-eared owls there (Blem et al. 1993). Similar high percentages have been reported from other areas of North America (Clark 1975). Nevertheless, evidence gathered from my study area in Park County, Wyoming suggests some degree of dietary flexibility: other prey may be important---perhaps on a seasonal basis. Deer mice (Peromyscus maniculatus), shrews (Soricidae), small birds, and insects typically represent a small portion of the diet of short-eared owls (Clark 1975). The remains of several fragmentary geomyid skulls collected from pellets in my study area (Dry Creek, Park County, Wyoming) indicate that pocket gophers are also taken.
Habitat
In general, short-eared owls prefer open habitats and can be found in a variety of community types across their wide geographical range (Howard and Griffith 1994). This includes freshwater and saltwater marshes, coastal plains, tamarack-black spruce bogs, prairies and sagebrush steppes, wet meadows, open shrub-lands, and montane park-lands. This species avoids closed-canopy brush-land and forest but open pine forest and open hardwood forest are sometimes utilized. Nesting habitat and hunting habitat follow this same general pattern. Short-eared owls typically construct nests on dry ground in open areas having dense herbaceous cover (Howard and Griffith 1994). Birds appear to select sites based on both thickness and height of the cover. Some studies indicate that short-eared owls show a preference for nesting in grassy areas (Clark 1975; Weller et al. 1955). Hunting habitat also consists of open ground where short-eared owls can find suitable prey. In my study area, owls hunt a riparian corridor no doubt concentrating on the grassy areas where voles often construct runways.
Territories
Short-eared owls typically maintain and defend all-purpose territories for breeding and hunting (Clark 1975). Major differences in mean territory size (44 to 339 acres) probably reflect prey availability and numbers. Clark (1975) studied short-eared owls in the same areas for two consecutive years and found significant differences in territory size (an average decrease of nearly 117 acres from one year to the next): he attributed this difference to variability in the food supply over the two year period.
Flight
Short-eared owls often exhibit a characteristic "flopping flight" pattern sometimes described as moth-like (Grondahl and Schumacher 1997). This soft and wavering flight is characterized by slow, deep wing-beats (World Owl Trust 1998) and is often supplemented with gliding. Short-eared owls use this type of flight when flushed from a roost-site, in display, and for hunting. In my study area, short-eared owls flushed from their roosting sites, typically flew only a short distance (almost always within 2 meters of ground level) and then glided to a new perch. In many instances, this routine was followed several times before the owl left the immediate area. Despite exhibiting the characteristic flight pattern after flushing, owls tended to be inconspicuous due to the short distance travelled, low-level flying, and coloration of their plumage. Conversely, the characteristic moth-like or flopping flight of this species may sometimes be conspicuous (Clark 1975). Field observations of exaggerated wing beats (in which the wings are brought high over the back), wing-clapping below the body, and hovering while presenting the talons suggest that flight may sometimes function in intraspecific aggressive display. Short-eared owls also sometimes circle buzzard-like around intruders while on the breeding territory (World Owl Trust 1998) or when juveniles are present later in the year (based on owls in my study area). Under other circumstances, some of these displays (the wing-clap inn particular) may be important in sexual recognition and courtship. Hunting flights generally involve quartering across fields (or other open areas), circling and gliding close to the ground, and nearly vertical drops (with wings upheld) to capture prey (Grondahl and Schumacher 1997).
These owls, like American kestrels and rough-legged hawks, also use hovering flight when hunting: a coursing short-eared owl often hovers prior to pouncing, especially if heading upwind (the preferred hunting direction) and may also hover to examine an area for prey (Clark 1975). My own observations and those of Clark (1975) suggest that individual short-eared owls may utilize the wind to hover with a minimal expenditure of energy. Hunting Strategies and Hunting Success Unlike most other owls, short-eared owls may hunt both day and night. In general, daytime hunting corresponds to a crepuscular activity pattern but on rare occasions I have observed owls hunting in the afternoon on overcast days. Clark (1975) suggested that short-eared owls hunt during the day in response to a diminished food supply and actually prefer to hunt in the hours approaching dusk and during the night; evidence from my study area generally supports this view. This species maintains flexibility relative to hunting in other ways as well. Short-eared owls preferentially hunt on the wing but occasionally they use a perch such as a fence-post or sapling (Clark 1975; Howard and Griffith 1994). Individual owls sometimes utilize this technique in unfavorable weather; it involves searching the nearby ground from an elevated perch and launching when prey is detected. Hunting success for short-eared owls from both perches and on the wing appears high, especially when contrasted with the limited data available on other birds of prey. Clark (1975) reported a 20.7% success rate for pounces over a three-year study period; conversely Rudebeck (1950) reported only a 10.8% success rate for sparrow hawks. Exploitation of Seasonally Abundant Food Short-eared owls often congregate in areas of high microtine rodent populations; in fact, this may be the key factor relative to migration in this species (Howard and Griffith 1994). Meadow vole (Microtus pennsylvanicus) populations in particular are often cyclic (two to five years) and thus are characterized by pronounced fluctuations in numbers (Clark and Stromberg 1987; Fitzgerald et al. 1994). Field research and anecdotal observations indicate that large numbers of short-eared owls often migrate into an area to take advantage of seasonal and/or annual abundance of such prey populations (Clark 1975; Weller et al. 1955). The species also exhibits some reproductive plasticity in response to prey numbers: clutch sizes seem at least partially tied to abundance of prey.
Feeding Behavior
When prey is captured, short-eared owls usually quickly dispatch it by crushing the occipital area with their beaks (Short and Drew 1962; Clark 1975). With a single exception, all of the skulls recovered from pellets in my study area showed evidence of this behavior. Short-eared owls generally consume prey on the ground near but not at point of capture (Clark 1975). Laboratory observations (using white mice) indicate that the head is consumed first, followed in turn by the rib cage, most of the viscera (the intestine is pulled out and discarded), large portions of the skin, and finally the posterior one-third of the body; feeding in the two instances observed required five and ten minutes respectively (Short and Drew 1962). Digestion time varies depending on type and weight of the prey taken: Clark (1975) reported a minimum time of 2 hours and 10 minutes. Following digestion, short-eared owls eject cylindrical or tear drop shaped pellets (approximately 5 cm in length and weighing approximately 4 grams) which contain bone, hair, and other indigestible or partially digestible material (Short et al. 1962). In addition to quantity of food, the temporal pattern of feeding affects pellet formation and regurgitation (Clark 1975). Most studies indicate that short-eared owls cast 1 to 2 pellets per day - usually at the roosting site. Typical pellets contain the skeletal remains of a single prey and include one skull paired with two mandibles and two innominates (Short et al. 1962). Fresh pellets recovered from my study area (Peromyscus sp. = primary prey ) were dark gray in color, averaged 4.6 cm in length, and 2 cm in width; after dessication and weathering these pellets turned light gray and appeared to lose much of their initial (albeit nominal) weight.
Roosts
Short-eared owls typically roost on the ground although they also sometimes use low brush, brushpiles, fenceposts, and telephone poles (Howard and Griffith 1994; Short and Drew 1962). In some areas after the onset of winter, this species roosts communally in coniferous trees (Clark 1975; Basakowski 1986). Communal roosts may also be encountered in areas with abundant prey (Clark 1975). Most short-eared owl roosts share common characteristics including shelter from the weather, location at the edge of or within the hunting area, and freedom from human disturbance. In my study area, short-eared owls roost in mountain big sagebrush (Artemesia tridentata var. vaseyana) growing in a shallow draw (Knight 1994). The owls appear to select individual plants for roosts based on height, canopy foliage, and proximity to the deepest portion of the drainage. Evidence obtained in the field (i.e. pellet distribution and "painting" on branches), suggests that the short-eared owls here usually roost on low-lying branches within 50 cm of ground level. The owls in this particular area often appear reluctant to leave the roosting site and their cryptic coloration undoubtedly allows them to avoid detection here on a regular basis.
Life Cycle Courtship and Mating
Short-eared owls form pair bonds in late winter or early spring (Howard and Griffith 1994). Clark (1975) observed that abandonment of communal roost sites by resident short-eared owls (followed by return to local territories) and male courtship flights signaled the onset of the breeding season. These high-altitude courtship flights include vocalizations ("Hooh, hooh, hooh" given approximately 15 times), audible wing-claps, and dives between calls (Holt et al. 1990; The Nature Conservancy 1996). Female short-eared owls may issue calls ("Kee-ow") in response to male courtship flights (Clark 1975). In addition to ritualized flight, males often feed females to help cement the pair bond and foster female receptivity. Mating itself is a brief affair: one observer reported that the process took 4 seconds, after which the male and female flew in opposite directions (Doan 1997). The pair bond persists however until after the young fledge and become self-sufficient; whether pairing lasts past the breeding season is unknown. Evidence from my study area suggests that pair bonds may indeed last from one year to the next at least for "resident" short-eared owls.
Nesting, Incubation, and Brooding
Short-eared owls typically construct their own nests on the ground: this is an usual behavior compared with that of most other owls. Nests typically consist of roughly circular scrapes lined with grass; nesting sites are generally located in dense vegetation offering concealment from the sides, though not necessarily from above (Clark 1975; Howard and Griffith 1994). Clark (1975) speculated that female short-eared owls are responsible for at least some of the nest construction; whether both sexes engage in nest building remains unknown. Egg laying follows nest building. In North America, egg-laying dates vary depending on latitude (Howard and Griffith 1994). Southern California populations nest first (as early as March) followed in turn by populations in the Midwest (April-June), northern United States (April-June), southern Canada (April-June), and northern Canada/Alaska (June-July). Female short-eared owls lay eggs asynchronously from 2 to 7 days apart (Howard and Griffith 1994); the elliptical white eggs become colored (soiled) with time (Clark 1975). Clutch size appears directly linked to latitude and availability of prey but averages between 5 and 7 eggs. Most North American populations of short-eared owls are single brooded but double broods may occur in the south (Howard and Griffith 1994). Only female short-eared owls incubate and brood clutches (Clark 1975). During incubation (and brooding), the male supplies the female with food (Howard and Griffith 1994) and provides distraction ("wounded bird" flights) if the nest is approached too closely (Clark 1975). Females will re-nest (usually within two weeks) if clutches are destroyed---second clutch sizes are smaller. Incubation time is approximately 26 days per egg (Holt et al. 1990) with young hatching asynchronously (Howard and Griffith 1994). Hatching rates reported in the literature vary between 60% and 90%. Hatchlings are blind at birth and covered with whitish down; the eyes are open by 9 days at which time they also cast their first pellet (Illinois Natural History Survey 1998). The young develop rapidly and typically leave the nest on foot (before fledging) at about two weeks of age (Clark 1975). Although they often capture insects at this stage of their lives (Clark 1975), the young remain dependent on their parents for most of their food up to and past fledging which occurs at approximately 29 days of age (Howard and Griffith 1994). The young of short-eared owls exhibit food begging behavior during this time which includes calling ("Psssss-sip"), feather ruffling, and wing fluttering (Clark 1975). Despite the attention of both parents, only about 50% of the young hatched survive to fledging (Howard and Griffith 1994).
Training
Some evidence suggests that adult short-eared owls provide training to their older offspring relative to searching for food. Clark (1975) reported 3 different instances of adult owls flying in and dropping prey near where their young were situated rather than passing it to them directly. This appeared to be an intentional act by the adult to encourage the young to search for food. Young short-eared owls also probably learn to hunt by imitating their parents. Clark (1975) reported at least one instance of a fledgling "mimicking" the hunting behavior of it's parent.
Longevity
Captive short-eared owls have lived to 15 years; the life-expectancy of wild birds remains unknown but is probably variable depending on ultimate factors present in a given area (Howard and Griffith 1994). Mortality Factors Mortality in short-eared owls results from direct and indirect action by humans, natural predation, and naturally occurring diseases. Short-eared owl mortality attributable to humans includes illegal shooting, collision with aircraft, trains, and automobiles, becoming fatally entrapped by barbed-wire, mutilation by farm machinery, predation by feral cats and dogs, and pesticide poisoning (Clark 1975; Marti and Marks 1989). Natural mortality in short-eared owls results from predation and disease (Clark 1975). Major predators of short-eared owls include a number of the larger birds of prey (great horned owls; snowy owls; rough-legged hawks; marsh hawks); rats, gulls, skunks and badgers are ground nest predators and may impact short-eared owl populations in some areas. In my study area, coyotes probably are the primary predator of the short-eared owls found there; magpies living in the area may be nest predators. Natural diseases of short-eared owls reported in the literature include fowl tuberculosis and fowl cholera (Clark 1975); the communal roosting habits of this species doubtless increase vulnerability to these particular diseases.
Conservation/Conclusion
Conservation represents a serious concern for short-eared owls despite their large range in North America. Habitat loss represents the single greatest threat to short-eared owl populations: declining numbers have been noted in many areas of the United States since 1900 (Howard and Griffith 1994; Sauer et al. 1995). These marked declines, observed in coastal areas, the Midwest, the northeast, the southern Great Plains, and southern and central California can largely be attributed to urbanization and agricultural development. Reforestation of grassland habitats following abandonment of farming may also decrease habitat available to short-eared owls (Partners in Flight 1997). As a result of declining numbers, California and Minnesota list short-eared owls as a species of special concern; the species is considered endangered in Michigan, Illinois, New Jersey, Massachusetts, and Pennsylvania (Howard and Griffith 1994; Michigan DNR 1991; Illinois Natural History Survey 1997; New Jersey Audubon Society 1997; The Raptor Center 1997; Pennsylvania DCNR 1998). Similarly, the Canadian government identifies short-eared owls as "vulnerable" throughout their range in Canada, again mostly due to threats resulting from development (Environment Canada-Canadian Wildlife Service 1997). Over most of the western United States, populations appear stable; certain agricultural practices probably represent the most serious threats in this region and in the Canadian prairie provinces as well (Sauer et al. 1995). In particular, overgrazing may remove cover needed for nesting and brooding (Howard and Griffith 1994) and probably indirectly increases vulnerability to mammalian predators (Marti and Marks 1989). In my study area, the shallow draw where short-eared owls typically roost shows definite signs of overgrazing (i.e. only minimal grass cover below large sagebrush plants and invasion of cheat grass): this could have contributed to the mortality (predation) of at least two adult short-eared owls in early 1998. It follows that the best approach for conservation of this species entails curbing or limiting urban expansion into areas of suitable habitat (especially grasslands, prairies, and coastal marshes). A secondary, nevertheless important, consideration should be the regulation of certain agricultural practices. Short-eared owls often persist near farmland borders if agriculture is not intensive; intensive agriculture or conversion of meadows, wetlands, and other habitats into cropland results in population declines (Howard and Griffith 1994). The probable adverse effect of overgrazing on this species, while not adequately documented, also suggests that greater regulation and monitoring of grazing might pay dividends in terms of short-eared owl conservation (Marti and Marks 1989).
