Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: south-central British Columbia, southern Alberta, southern Saskatchewan, southern Manitoba south through western U.S. and central Mexico to Panama (AOU 1983, Haug et al. 1993). NON-BREEDING: Withdraws from northernmost portions of breeding range. Winters regularly to El Salvador, casual to accidental to western Panama (AOU 1983). California, New Mexico, and Arizona are important wintering areas in the U.S. (James and Ethier 1989).

Comments: Optimum habitat typified by short vegetation and presence of fresh small mammal burrows (Zarn 1974). Found in open grasslands, especially prairie, plains, and savanna, sometimes in open areas such as vacant lots near human habitation (e.g., campuses, airports, golf courses, perimeter of agricultural fields, banks of irrigation canals). In Northern Great Plains of U.S., preferred grassland on aridic ustoll and typic boroll soil types where vegetation was heavily grazed by small mammals (Kantrud and Kologiski 1982). In Canadian prairies, burrowing mammals and owl habitat associated with lacustrine soils (Wellicome and Haug 1995). Spends much time on the ground or on low perches such as fence posts or dirt mounds.

Nests and roosts in abandoned burrow dug by mammal (especially prairie dog, also ground squirrel (CITELLUS SPP.), badger (Taxidea taxus), fox, woodchuck (Marmota monax), tortoise). In Imperial Valley, California, associated with ground squirrels (Cuolombe 1971); in Great Plains, chiefly associated with prairie dogs. Rarely excavates own burrow, preferring to enlarge or modify existing burrow. Nests in lava cavity in some areas. Abandoned burrows soon become unsuitable for nesting. Livestock dung used in some areas to line burrow entrance, reducing detection by predators (see Green and Anthony 1989). Uses satellite burrows around nest burrows, moving chicks at 10-14 days presumably to reduce risk of predation. Pattern of burrow use influenced by availability, soil, dynamics of prairie dog population, and other owls (Desmond and Savidge 1998).

Owls concentrate nocturnal foraging effort in areas with high small mammal abundance (e.g. deer mice [Peromyscus maniculatus] and meadows voles [Microtus pennsylvanicus]), which account for the bulk of their caloric intake (Wellicome 1997b). In Saskatchewan, preferred foraging habitat was in dense, permanent grass-forb vegetation > 30 cm high in uncultivated areas and rights-of-way; tended to avoid cultivated cropland and pasture (Haug and Oliphant 1990). Diurnal foraging chiefly for invertebrates and concentrated around vicinity of nest burrow (Haug and Oliphant 1990, Haug et al. 1993).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Chiefly migratory in the northern portion of range (some birds may overwinter). Some U.S./Canadian breeders winter in Mexico and possibly in Central America (James and Ethier 1989). Canadian breeders are believed to winter south of the U.S.-Mexico border. Arrives in northern breeding range April-May. Of thousands of birds banded in Canada, only a few recovered in U.S. and none in Mexico, but returns reported from Texas and Gulf Coast in spring and fall (Holroyd and Wellicome 1997). Canadian radio-telemetry migration tracking project traced birds from Saskatchewan to North Dakota in autumn (Scalise 1998). More than 99% of an Oklahoma study population was migratory (Butts 1976). Possible wintering population in Texas coastal lowlands and northern Mexico, however much of this area is cultivated or prairie dog colonies are vacant (Holroyd and Wellicome 1997). Breeding population in southern California apparently sedentary.

Comments: Feeds primarily on large insects (especially in warmer months) and rodents; sometimes eats birds and amphibians. Catches prey in flight or drops to ground.

10,000 - 100,000 individuals

Comments: Extirpated from British Columbia by 1980 with reintroduction efforts begun in 1983; fewer than 10 pairs currently reported (James and Espie 1997, Low and Leupin 1998). In 1998, two known nesting pairs remaining in Manitoba and population estimated at 10 to 20 pairs (De Smet, pers. comm.). Iowa reports fewer than 10 pairs, eight states estimate 100 to 1000 pairs, nine report 1000 to 10,000 pairs, and Texas estimates more than 10,000 pairs (James and Espie 1997). California contains a major portion of western population with over 9000 breeding pairs; 71% of which occur in the Imperial Valley (Barclay et al. 1998, DeSante et al. 1997).

Reported densities: 0.8 pair per hectare in agricultural lands along Colorado River in Arizona (Brown 1998); 8 pairs per square kilometer in California, 3.5-6 hectares per pair in North Dakota, 13-16 hectares per pair in Saskatchewan. Numbers increased but density decreased with increasing size of prairie dog (Cynomys spp) town in Nebraska (Desmond and Savidge 1996). In large prairie dog towns (> 35 hectares), owl distribution found to be less dense but clumped, and clumping was not related to burrow availability (Desmond et al. 1995.)

Badger (Taxidea taxus) predation observed to be higher in colonies with lower density of prairie dogs (Desmond and Savidge 1998).

Desmond and Savidge (1998) observed a time lag in response to decline in density of active prairie dog burrows, suggesting that nest site fidelity may be strong despite dramatic change in habitat quality.

Territory defense mainly limited to immediate vicinity of nest burrow; may share foraging area. Home range in Saskatchewan: 0.14-4.81 per square kilometer; 95% of all movements within 600 meters of nest burrow (Haug and Oliphant 1990).

Clutch size averages six to seven. Incubation, by female, lasts 27-30 days. Male provides food during incubation and early nestling stages. Young run and forage at four weeks, sustained flight at six weeks. Averages three to five fledglings per brood. First breeds at one year (some may not); generally one brood per year. Weather plays a strong and unpredictable role in abundance and availability of small mammal prey, which in turn can limit reproductive success (Wellicome 1998).

Canada

Rounded National Status Rank: NNRB - Unranked

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: T4 - Apparently Secure

Global Short Term Trend: Decline of 10-50%

Comments: Declining in Arizona, California, Colorado, Kansas, Nebraska, Nevada, Utah, and Washington (James and Espie 1997). No western states or provinces report increasing populations (James and Espie 1997). In California, 60% of known breeding groups disappeared between 1980s and 1990s (Barclay et al. 1998, DeSante et al. 1997). In Santa Clara County, California, 60% of owl locations were replaced by development, 1991-1994 (Buchanan 1997). Expected to be extirpated in areas of central California within 10 years (Holroyd and Wellicome 1997). Declining in Great Plains of U.S. where it is strongly associated with prairie dog (Cynomys SPP.) towns, which have been greatly reduced by cultivation and poisoning. Extirpated in Minnesota by 1992 and reintroduction attempts failed (Martell et al. 1998). Montana population estimated at 300 pairs; trend unknown although prairie dog colonies have declined by 88%, 1910s-1980s (Knowles 1998, Holroyd and Wellicome 1997). In North Dakota, is nearly extirpated east of the Missouri River; west of the Missouri occupancy dropped 30% to 50% on prairie dog towns 1991 to 1996 (Murphy et al. 1998). Populations in western Nebraska declined 58% (91 to 38 nesting pairs), 1990-1996 (Desmond and Savidge 1998). Of five populations in New Mexico, three are stable or increasing (Finley and Arrowood 1998). In Wyoming, only 11% of 86 historical sites occupied in 1998 (Korfanta et al. 1998). Declined in Canada from the mid-1970s through the early 1990s (Kirk et al. 1995); declined 50% or more in some areas (Dundas and Jensen 1995). No complete survey in Canada, but variety of studies show widespread range contraction and declining density (Hjertaas et al. 1995). Declining in Alberta and Saskatchewan at >10% per year (Holroyd and Wellicome 1997). In Alberta, population estimate dropped from 1500 to 800 birds (47%), 1978-1990 (Wellicome 1997b). In Saskatchewan, Operation Burrowing Owl reports 87% decline in site occupancy, and 88% decline in number of pairs, 1988-1997, despite a doubling of observer effort (Skeel et al. 1998). Number of young per successful nest declined from 5.5 to 3.5 in Alberta (Wellicome, pers. comm.). In Manitoba, young per successful nest decreased from 5.5 to 4.1, 1987-1996, but was attributed to weather patterns (De Smet 1997). In Saskatchewan, number of young per nesting attempt dropped from 4.0 to 1.5, 1986-1993 (James et al. 1997). Loss of habitat in Canada was substantial between 1976 and 1986, has slowed considerably since then, but declines have continued. If present trends continue, extirpation from Manitoba will occur within a few years and extirpation from all of Canada may occur within a few decades (Wellicome and Haug, 1995). Although ranges throughout much of Mexico, its status and trends are unknown. Black-tailed prairie dog (Cynomys ludovicianus) colonies are vacant or plowed under in many areas (Holroyd and Wellicome 1997, Rodriguez Estrella et al. 1998).

Global Long Term Trend: Increase of 10-25% to decline of 70%

Comments: Rangewide estimates not available, but loss of habitat to cultivation, loss of prairie dog towns, etc. has been considerable. Undoubtedly has declined substantially in central plains and in California. Over past 100 years, DeSante and George (1994) estimate population declines > 50% in British Columbia, Alberta, California, Nevada, Colorado and New Mexico. In California, there has been a general decline from the 1950s into the 1990s, accelerating in the last 20 years (Barclay et al. 1998, DeSante et al. 1997). In California, there has been a general decline from the 1950s into the 1990s, accelerating in the last 20 years; 60% of known breeding groups disappeared between 1980s and 1990s (Barclay et al. 1998, DeSante et al. 1997). In a San Francisco Bay and Central Valley census, occupancy of historic breeding locations declined by 38% and the number of breeding groups dropped 52%, 1986-1991. The proportion of census area occupied by owls declined 50%, 1981-1991; and the species was extirpated from four coastal counties (DeSante et al. 1997, Ehrlich et al. 1992).

Comments: Primary threats across North American range, including Mexico, are habitat loss and fragmentation primarily due to intensive agricultural and urban land conversion, and habitat degradation due to control and extermination of colonial burrowing mammals (Dundas and Jensen 1995, Haug et al. 1993, Rodriguez Estrella et al. 1998, Sheffield 1997). Dramatic 98% reduction of prairie linked to reduction of owl population (Evans 1982, Sheffield 1997). Fragmentation and isolation are threats to small and localized populations that may be more prone to extinction. Johnson (1997) observed a wild population of < 50 owls go extinct in half the time predicted by a deterministic model. Scarcity of nesting habitat may reduce opportunity for unpaired owls to find mates (Sheffield 1997). In California, 90% of population found on private land (Trulio and Rosenberg 1998) and many habitat areas are threatened by intensive development, particularly conversion of irrigated croplands for housing (Barclay et al 1998, Salmansohn 1993).
Usually tolerant of human activity but vulnerable to predation by dogs and cats. With habitat alteration and the extermination of top predators (e.g., wolves [CANIS spp]), subsequent increases in small predators such as foxes, badgers (Taxidea taxus), and coyotes (Canis latrans) may also be taking a large toll on burrowing owls (Sheffield 1997, Wellicome 1997b). In Minnesota, high predation rates played role in failure of four years of reintroduction efforts (Martell et al. 1998). On Santa Barbara Island, California, heavy predation by barn owls (Tyto alba) during a time of small mammal scarcity resulted in extirpation of the fall-winter resident population (Drost and McCluskey 1992). Eleven states and provinces also report pesticides as a factor in declines (James and Espie 1997). Other threats include vehicle collisions, predators, persecution, harassment by dogs, collapse of burrows, and food availability (Clayton and Schmutz 1997, Erickson 1987, Haug and Didiuk 1991, James and Espie 1997, see also Wedgwood 1979, Wellicome and Haug 1995).

Restoration Potential: Restoration potential hinges on sustaining burrowing mammal populations, particularly prairie dog and ground squirrel colonies, for adequate nesting habitat, as well as roosting and foraging habitat during migration and winter. Still relatively widespread throughout the West, but factors reducing survival and the demographics of increasingly fragmented and isolated populations are still poorly understood for effective restoration.

Reintroduction may be desirable where extirpated and suitable habitat exists. Reintroduction efforts in British Columbia, Manitoba, and Minnesota, however, have not succeeded in establishing self-sustaining populations, chiefly due to low migratory returns (Trulio 1997b).

Preserve Selection and Design Considerations: Apparently sensitive to habitat fragmentation and isolation. Larger home ranges have been observed in fragmented landscapes (Warnock and James 1997). Higher post-fledging mortality from vehicle collisions were observed in a fragmented agricultural landscape (> 90% of land area under cultivation) compared to an unfragmented rangeland (< 20% cultivation; Clayton and Schmutz 1997). Work in California suggests survival in urbanized landscapes may be enhanced if they include necessary habitat features: short-grass sites for nesting, presence of burrowing mammals (e.g., ground squirrels) and large open fields for foraging (Trulio 1997a).

A study in fragmented Saskatchewan grasslands (Warnock 1997, Warnock and James 1997) indicates that habitat quality (particularly the presence of lacustrine soils and associated burrowing mammal populations) and proximity to other occupied sites are important factors in site selection. Where quality habitat is limited, may use the best remaining sites rather than the largest or least fragmented habitat patches. However, persistence on sites for more than four years increased where there were larger numbers of neighboring occupied sites; where habitat patches had more continuity with other natural habitats within 20 kilometers; and where sites had less patch edge.

Researchers suggest that predation likely has heavy impacts in fragmented landscapes (Warnock and James 1997, Wellicome and Haug 1995). Studies of ground nesting prairie passerines show nest predation is higher in small habitat patches and near habitat edges with woody cover, where predators may concentrate effort (Burger et al. 1994, Johnson and Temple 1990); this pattern may hold true for owls, but is not quantified. It has also been suggested that crowding in small habitat patches increases foraging competition, reduces nest productivity, and increases nest abandonment, but these issues have received little research attention (Green and Anthony 1989, Warnock and James 1997).

Small populations (e.g., < 50) may be more prone to extinction (Johnson 1997). At range peripheries may also show higher rates of extirpation and lower rates of occupancy and colonization (Warnock 1997).

Management Requirements: BURROWING MAMMALS: Conserving burrowing mammal colonies is of primary importance to sustaining viable populations. Prairie dog and ground squirrel colonies should be protected as an integral part of grassland and prairie ecosystem conservation. Reduction and removal of burrowing mammal colonies, especially prairie dogs and ground squirrels, eradicates owls (Butts and Lewis 1982, Haug et al. 1993, Olenick 1989). In Oregon, Nebraska, and likely elsewhere, badgers (Taxidea taxus) are also important for providing burrows (Desmond and Savidge 1996, Green and Anthony 1989).

VEGETATION MANAGEMENT: Management for short grass (< 5 cm; e.g., by grazing, burning) is beneficial, as long as burrowing mammals are allowed to persist to provide fresh burrows, and a prey base of small mammals and invertebrates is available. In vegetation > 5 cm, elevated perches are important for hunting and predator detection (Green and Anthony 1989). Enough permanent cover and tall vegetation (e.g., 30-60 cm reported in Canadian prairie) to provide habitat for prey is also necessary, especially as prey availability during brood rearing has been shown to limit brood survival in highly fragmented habitats (Wellicome 1997a, Wellicome et al. 1997). In Columbia Basin of Oregon, intensively grazed snakeweed preferred for nesting (Green and Anthony 1989). May benefit from periodic burning of desert grasslands (see Dodd 1988). Intensive cultivation causes loss of burrows and foraging habitat, reduces quality of nesting habitat, increases vulnerability to predation, and may reduce opportunity to find mates (Haug et al. 1993).

PESTICIDES: The effects of contaminated prey and extent of indirect mortality are largely unknown (Haug et al. 1993), however pesticide use should be avoided within vicinity of burrows. Carbofuran reduces survival and reproductive success and should not be applied near nest burrows (Haug et al. 1993). In Canada, Carbofuran application prohibited within 250 m of nests. Strychnine-coated grain used to control ground squirrels did not cause direct mortality, but was linked to significantly reduced weights in breeding adults, either due to sublethal effects or a drop in prey availability (James et al. 1990). Should be monitored for impacts where pesticides are applied (Haug et al. 1993, Sheffield 1997).

PERSECUTION: Should be protected from shooting, particularly where they may be taken incidentally by people shooting prairie dogs and ground squirrels. Wedgewood (1979) reported three colonies destroyed by shooting. In an Oklahoma study 66% of mortality was due to shooting (Butts 1976); the extent of the problem is unknown (Haug et al. 1993).

HUMAN ACTIVITY: Nesting areas and burrows should be protected from intensive disturbance during incubation. At a study site on a municipal airport, Thomsen (1971) estimated 65% of damage to burrows caused by humans, 20% by dogs from nearby neighborhoods. Dogs also elicited frenzied defense. Otherwise tolerant of moderate levels of human activity and vehicle traffic, and can nest successfully in some agricultural areas, golf courses, airports, and college campuses where burrows and prey are available (Botelho and Arrowood 1996, Haug et al. 1993, see also Plumpton and Lutz 1993). Nesting on airports may create an collision hazard; however short-distance relocation away from high-speed traffic areas is possible (Barclay 1998).

ARTIFICIAL BURROWS: Artificial nest burrows (ANBs) have been used successfully to augment nesting habitat where mammal burrows are limited, where owls have been evicted from natural burrows, and in reintroduction efforts (Collins and Landry 1977, Trulio 1997b). In Idaho, were induced to use ANBs (Olenick 1990). Leaving dirt berms at the edge of cultivated fields may be beneficial, with the additional ANBs where burrowing mammals are gone (Olenick 1989). Use of ANBs also allows close study of nest success (Henny and Blus 1981, Wellicome 1997a).

TRANSLOCATION: Relocation may be desirable where nesting habitat is immediately threatened by development and cannot be protected. Relocation often involves use of ANBs and supplemental feeding. See Harris and Feeney (1990) for information on the successful relocation from a construction site to an enhanced site on an unused portion of a municipal golf course in central California. Relocation has also been partially successful where moved long distance at the beginning of the breeding season (Delevoryas 1997). Site fidelity may interfere with translocation efforts, and mortality at new sites is a risk (Delevoryas 1997, Feeney 1997). Trulio (1995) describes a method of passive relocation, by placing artificial burrows within 100 m of burrows to be destroyed. Short-distance relocation of burrows when chicks were 27 to 45 days old was only partly successful in Idaho (Smith and Belthoff 1998). Sites for relocation must be managed to increase the chance of survival and persistence (Delevoryas 1997). Trulio (1997b) suggests that management methods that keep birds near nest burrows may be more successful in protecting birds than relocating out of nest territories.

Management Research Needs: Rates of habitat conversion and degradation (e.g., agricultural conversion or decline in burrowing mammal colonies) rarely reported and more work is needed to determine rate and extent of habitat loss (James and Espie 1997). Limits on productivity and survivorship need to be better understood, particularly in Canada where declining faster than loss of breeding habitat (Holroyd and Wellicome 1997). Factors affecting survival during migration and on wintering grounds also unknown. Metapopulation dynamics, influence of landscape patterns, and the effects of fragmentation and isolation on populations are little studied. Although some work exists on Carbofuran, studies of many other pesticides used in habitat are needed also (James and Espie 1997). Indirect and sublethal effects of pesticides unknown. Extent of mortality and vulnerability to shooting, particularly during prairie dog and ground squirrel control, generally unknown and unquantified. Management strategies currently in use need to be evaluated for their effectiveness. Further investigations also needed on land use impacts; prescribed fire; disturbance; habitat enhancements (e.g., artificial burrows and perches); relocation and reintroduction; impact of predators on nest success (Millsap et al. 1997, Sheffield 1997).

Biological Research Needs: Movement patterns, timing, and ecology during migration and winter are little known. Very few studies have been carried out in Mexico, Central, or South America. The rapid population decline in Canadian provinces despite apparent availability of suitable habitat suggests unknown factors in winter and migration may be affecting survival (Schmutz 1997). See Millsap et al. (1997) for literature gaps on aspects of life history and ecology, including disease, habitat, migration, molt, mortality, mutualisms, roosting, sexual dimorphism, soils, taxonomy and vocalizations.

Stewardship Overview: Intertwined with conservation of prairie ecosystems in general and burrowing mammal colonies in particular. Suffering dramatic declines and range contraction throughout the West, chiefly due to habitat loss, fragmentation, and degradation tied to the widespread control and extermination of prairie dogs (Cynomys spp) and ground squirrels (CITELLUS spp), as well as the conversion of prairie, grasslands, and irrigated agriculture to intensive development. Protecting burrowing mammal colonies (with an emphasis on large colonies and unfragmented habitat) is critical to sustaining viable populations. Some research suggests a viable population is more than 50 birds. Widespread loss of habitat and burrowing mammals colonies is probably also taking a toll on survival during migration and winter. Habitat conservation and management must also include areas of higher grass-forb vegetation supporting ample small rodent and insect prey, particularly as owls are food-limited during brood rearing in some regions. Factors limiting reproduction and survival not fully known, but impacts include predation, vehicle collisions, pesticides, and shooting. Many individual studies and a volunteer effort in Canada (Operation Burrowing Owl) have tracked steep population declines in the last two decades; a standardized population survey and monitoring effort is needed across Canada, the U.S., and Mexico, as well as monitoring of population demographics and habitat. A tri-country working group has recently been established to promote monitoring, research, and conservation.

Species Impact: As a predator of rodents and insects, may be beneficial to agriculture where it is allowed to coexist.