Index of Species Information

WILDLIFE SPECIES:  Asio flammeus

Introductory

WILDLIFE SPECIES: Asio flammeus
AUTHORSHIP AND CITATION : Howard, Janet L. 1994. Asio flammeus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].
ABBREVIATION : ASFL COMMON NAMES : short-eared owl TAXONOMY : The currently accepted scientific name of short-eared owl is Asio flammeus (Pontoppidan) [1]. It is in the family Strigidae [28]. Only the type subspecies, Asio flammeus flammeus, occurs in North America. A. f. ponapensis, Ponape short-eared owl, occurs on the Caroline islands, and A. c. sandwichensis, Hawaiian short-eared owl, occurs on the Hawaiian islands [13,28]. ORDER : Strigiformes CLASS : Bird FEDERAL LEGAL STATUS : None OTHER STATUS : Information on state- and province-level protection status of animals in the United States and Canada is available at NatureServe, although recent changes in status may not be included.

WILDLIFE DISTRIBUTION AND OCCURRENCE

WILDLIFE SPECIES: Asio flammeus
GENERAL DISTRIBUTION : The short-eared owl occurs on all continents except Australia and Antarctica [5,12,28]. In North America, it is distributed from Alaska and all Canadian provinces except the Northwest Territories south through the conterminous United States to central Mexico. It also occurs on Pacific and Caribbean islands including Hawaii, Puerto Rico, and the Virgin Islands [12,22,23,28]. ECOSYSTEMS : FRES26 Lodgepole pine FRES28 Western hardwoods FRES29 Sagebrush FRES30 Desert shrub FRES32 Texas savanna FRES33 Southwestern shrubsteppe FRES34 Chaparral-mountain shrub FRES36 Mountain grasslands FRES37 Mountain meadows FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands FRES41 Wet grasslands FRES42 Annual grasslands< FRES44 Alpine STATES :
AL AK AZ AR CA CO CT DE FL GA
HI ID IL IN IA KS KY LA ME MD
MA MI MN MS MO MT NE NV NH NJ
NM NY NC ND OH OK OR PA RI SC
SD TN TX UT VT VA WA WV WI WY
DC PR VI
AB BC MB NB NF NS ON PE PQ
SK YT MEXICO
BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K022 Great Basin pine forest K030 California oakwoods K042 Creosotebush - bursage K043 Paloverde - cactus shrub K048 California steppe K049 Tule marshes K051 Wheatgrass - bluegrass K052 Alpine meadows and barren K053 Grama - galleta steppe K054 Grama - tobosa prairie K055 Sagebrush steppe K056 Wheatgrass - needlegrass shrubsteppe K057 Galleta - three-awn shrubsteppe K058 Grama - tobosa shrubsteppe K061 Mesquite - acacia savanna K063 Foothills prairie K064 Grama - needlegrass - wheatgrass K065 Grama - buffalograss K066 Wheatgrass - needlegrass K073 Northern cordgrass prairie K074 Bluestem prairie K077 Bluestem - sacahuista prairie K079 Palmetto prairie K080 Marl - everglades K088 Fayette prairie K092 Everglades K093 Great Lakes spruce - fir forest K094 Conifer bog SAF COVER TYPES : 13 Black spruce - tamarack 37 Northern white-cedar 38 Tamarack 68 Mesquite 209 Bristlecone pine 242 Mesquite 250 Blue oak - Digger pine SRM (RANGELAND) COVER TYPES : NO-ENTRY PLANT COMMUNITIES : The short-eared owl occurs in most open plant communities in North America [12,13,21,22,28]. Taiga is usually used only in late summer [12]. The owl avoids tundra and closed-canopy brushland and forest [12,21,22,32].

BIOLOGICAL DATA AND HABITAT REQUIREMENTS

WILDLIFE SPECIES: Asio flammeus
TIMING OF MAJOR LIFE HISTORY EVENTS : Age at sexual maturity - 1 year [27] Courtship and breeding - Short-eared owl form pair bonds; whether the pairing lasts past the breeding season is unknown [27]. Depending upon latitude, courtship begins in mid-winter or early spring, and breeding is completed by late winter or late spring. In Idaho and Massachusetts, courtship begins in March and the female lays eggs by May [2,24]. In Illinois, courtship begins in late April and egg-laying is complete by early May [28]. Nesting and incubation - Most North American populations are single-brooded, although short-eared owls in the South are sometimes double-brooded. Clutch size varies from 2 to 14 eggs, with 5 to 7 eggs being the norm [28]. The female tends to lay more eggs when prey populations are high [13]. Murray [37] found that clutch sizes were significantly larger with increasing latitude; he attributed this to larger rodent populations in the North. The female lays her eggs asynchronously, from 2 to 7 days apart. Regional egg-laying dates are given below [28]. Alaska and arctic Canada: June 5-July 2; usually June 10-June 25 southern Canada: April 30-June 22; usually May 4-June 17 northern United States: April 14-June 15; usually April 23-June 10 Midwest: April 4-June 8; usually April 16-May 25 southern California: March 20-May 18; usually March 26-April 26 Destroyed clutches are usually replaced within 2 weeks; second clutch sizes are smaller [12,28]. The female is the sole incubator; the male supplies her with food during incubation. Incubation time is 21 to 29 days per egg. The eggs hatch asynchronously, about one every 3 days. The brood therefore consists of different-aged sibs. The female does all brooding; the male hunts to feed the young and his mate [12,16,24,28]. Fledging - Young leave the nest on foot about 16 days after hatching and fledge at approximately 29 days of age [24,25]. The brood is dependent on the parents for food "for a period of time" after fledging [13]. After all young have fledged, parents lead the brood to a new area if prey is scarce on the nesting grounds [34]. Clark [12] reported a mean clutch size of 8.6 for short-eared owl nests in a Massachusetts freshwater marsh. An average of 7.0 young per nest hatched, and an average of 4.0 young per nest fledged. On Nantucket maritime heath, Tate and others [45] found a mean clutch size of 5.7 in 1985. An average of 3.4 eggs hatched, and 2.0 young per nest fledged. In 1986, mean clutch size was 7.7, with an average of 7.0 eggs hatching and 3.4 young per nest fledging. Migration - Much remains to be discovered about short-eared owl migration dates and routes. The short-eared owl is well adapted to heat and cold. As a result, it is apparently only weakly migratory [28]. Short-eared owl populations at the edge of the species' northern distribution move south in late summer or early fall, but it is unclear whether more southerly populations migrate or remain in an area as permanent residents. Banding records are few, but limited studies show that some individuals in populations south of taiga are regular migrants. Others are irregular migrants, leaving in some years but not others. Some owls probably migrate to new areas as young adults, then become permanent residents. Migration routes are generally north-south, but not always. Some migrants, for example, move back and forth from North Dakota and eastern Oregon [12]. Except for populations at climatic extremes, when entire populations migrate it is usually in response to depletion of the prey base rather than seasonal climate changes. Short-eared owl rapidly move out of an area bereft of prey, and rapidly move into areas where rodent populations are rising [12,29,34]. Longevity - Captive birds have lived to age 15. It is unknown how long short-eared owl usually survive in the wild [28]. PREFERRED HABITAT : Short-eared owl occupy a variety of open habitats within their wide geographical distribution. Preferred habitats include fresh- and saltwater marshes [6,7,12,21], coastal plains [24], tamarack (Larix laricina)-black spruce (Picea mariana) bogs [8], old fields [14,18], prairies [30], sagebrush (Artemisia spp.) steppes [38,40,42], wet meadows, grasslands, open shrublands, and montane parklands [21,22]. Since the species is only weakly migratory, nesting, hunting, and wintering habitats are generally the same [12,28]. In Massachusetts, short-eared owl in maritime heath occupied a home range of 63 to 198 acres (25-79 ha) [45]. In freshwater marsh, the home range was 184.8 to 303.5 acres (73.9-121.4 ha) [12]. Nesting habitat - Short-eared owl nest on dry ground in open areas with dense herbaceous cover. Even in wetlands, dry microsites are selected for nesting [13]. Taiga and tundra are poor nesting habitat [12]. Hunting habitat - The owl uses open ground where prey is available [7,33]. COVER REQUIREMENTS : Nesting cover - Short-eared owl require open areas with dense, tall herbs for nesting. They are the only North American owl that habitually build their own nest each year. Nesting short-eared owl build the nest with sticks and rotting vegetation; they approach it through a short tunnel in the thick grass [28]. Duebbert and Lokemoen [15] found that in North Dakota rangeland planted to smooth brome (Bromus inermis), intermediate wheatgrass (Thinopyrum intermedium), and tall wheatgrass (Elytrigia elongata), owls selected sites where grass cover was 12 to 24 inches (30-60 cm) tall. Seventy-five percent of nests were three-fourths concealed from the sides; tops were mostly open. Evrard and others [18] found that in a Wisconsin old field, nesting cover was mostly 3-foot (90-cm) quackgrass (Elytrigia repens). Hunting cover - Short-eared owl require open landscapes for hunting. They generally hunt on the wing, flying low [28], but occasionally hunt from low perches such as saplings and fenceposts [7]. Roosting cover - Short-eared owl usually roost on the ground or on grass tussocks, although they occasionally use low brush [28], fenceposts, and telephone poles [9]. During winter in snow country, they often roost communally in low-growing conifers [12,28,33,39]. Observers in New Jersey saw short-eared owl flocking together and roosting in short conifers whenever snow cover was greater than 30 inches (75 cm) [9]. FOOD HABITS : Unlike most owls, short-eared owl hunt both day and at night until sufficient prey are taken [12,28]. Throughout most of North America, the meadow vole (Microtus pennsylvanicus) is selectively hunted and comprises at least 90 percent of the short-eared owl's diet [5,12,14,26,28]. Clark [12] speculated that on this continent, short-eared owl cannot reproduce unless sufficient meadow vole are taken. Current knowledge of short-eared owl food habits and nutritional requirements is insufficient to determine whether this is true, however [50]. Minor items in the short-eared owl diet include other voles (Microtus spp.), deer mouse (Peromyscus maniculatus), shrews (Soricidae), and small birds [9,46,48]. In Hawaii, the house mouse (Mus musculus) and the Polynesian rat (Rattus exulans) are primary prey [22,42]. PREDATORS : Large avian predators such as great horned owl (Bubo virginianus) [4], snowy owl (Nyctea scandiaca) [33], and rough-legged hawk (Buteo lagopus) [36] occasionally prey upon both juvenile and adult short-eared owl. Ground-nest predators such as American badger (Taxidea taxus) [47] and gulls (Larus spp.) [12] eat the eggs. MANAGEMENT CONSIDERATIONS : Short-eared owl populations have declined over most of their former North American range due to habitat loss [24]. By 1986, they were widely reported as declining in the Hudson-Delaware region, the Midwest, and the Southern Great Plains; in severe decline in central-southern, prairie, and mid-Pacific coast regions; and long since extirpated from southern California [17]. In the Midwest, short-eared owl are currently reported only from remnant prairie [44]. Baldner [2] and Sinclair [43] attributed the species' rarity in Iowa to loss of tallgrass prairie. Urbanization of coastlands has decimated populations in Massachusetts [12,45]. Central California populations have been reduced by agricultural and urban development [21]. Marti and Marks [35] have listed populations as stable in Oregon and Colorado and fluctuating but stable in Montana. Short-eared owl often persist near farmland borders where agriculture is not intensive. Intensive agriculture or conversion of meadows, wetlands, or other short-eared owl habitat to cropland, however, results in short-eared owl decline [24,29]. Overgrazing removes cover needed for nesting and brooding [21,35]. In Idaho, short-eared owl were present in ungrazed big sagebrush-standard wheatgrass (Artemisia tridentata-Agropyron desertorum), but not in areas grazed by sheep [40,41].

FIRE EFFECTS AND USE

WILDLIFE SPECIES: Asio flammeus
DIRECT FIRE EFFECTS ON ANIMALS : Most adult birds escape fire [32]. Fire in early spring, before fledging occurs, probably kills some juveniles. Fire destroys some nests [28], but because many grass fires burn in a patchy pattern, some nests are skipped [28,30]. In northwestern North Dakota, June prescribed surface fires in western wheatgrass (Pascopyrum smithii)-blue grama (Bouteloua gracilis)- needle-and-thread grass (Stipa comata) prairie were set to test survival of ground-nesting birds. Twelve ground-nesting species, with a total of 177 active nests, were present before the fires. One was a short-eared owl nest. Fire skipped 31 percent and burned 68 percent of the 177 nests. Seven percent of the burned nests were partially burned and did not produce brood, and 5 percent were partially burned and had eggs hatch. The short-eared owl nest was burned and subsequently had eggs hatch [30]. In Massachusetts, an April wildfire in a sedge-rush (Carex-Juncus spp.) marsh burned over several short-eared owl nests. Clark [12] removed the two eggs within one burned-over nest and placed them in an incubator. They hatched, but the owlets appeared to have delayed visual development. The nest was not abandoned; the nesting female laid new eggs that Clark left in the nest. The new eggs hatched, and the owlets developed normally. Eggs of burned-over nests are highly vulnerable to ground-nest predators due to loss of cover. Ring-billed gull (Larus delawarensis) consumed eggs from some burned-over short-eared owl nests following the Massachusetts wildfire [12]. HABITAT RELATED FIRE EFFECTS : Fire was historically an important disturbance in many of the plant communities short-eared owl occupy. It created grass patches within shrublands, maintained the open structure of parklands, and prevented woody plant invasion of marshlands and grasslands. Although much of short-eared owl decline can be attributed to urbanization, at least some is probably due to succession of open plant communities to closed ones as a result of fire suppression. Expansion of eastern deciduous species into prairie, for example, has reduced short-eared owl habitat [32]. FIRE USE : Fire can maintain or expand short-eared owl habitat. Burning after the fledging stage, so that young owls are not lost to fire, is probably best [30]. Because summer or fall fires are usually more severe than spring fires, they would probably kill more woody vegetation, opening up habitat as well as avoiding damage to reproduction. Burning during the nesting season, however, does not totally eliminate reproduction of ground-nesting birds such as short-eared owl. Kruse and Piehl [30] recommended partial burning during the nesting season. Partial burns reduce cover less uniformly, but should result in higher recruitment of ground-nesting birds than would complete burns conducted during the nesting season.

REFERENCES

WILDLIFE SPECIES: Asio flammeus
REFERENCES : 1. American Ornithologists' Union. 1983. Checklist of North American birds. 6th ed. Lawrence, KS: Allen Press, Inc. 877 p. [21234] 2. Baldner, Russell P. 1984. Short-eared owls at Hayden Prairie. Iowa Birds. 54(3): 77-78. [22316] 3. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434] 4. Bluhm, Cynthia K.; Ward, E. Kevin. 1979. Great horned owl predation on a short-eared owl. Condor. 81(3): 307-308. [22254] 5. Borko, Martin. 1977. Short-eared owl food items in winter. Kingbird. 27(2): 80-81. [22502] 6. Bosakowski, Thomas. 1986. Short-eared owl winter roosting strategies. American Birds. 40(2): 237-240. [22249] 7. Bosakowski, Thomas. 1989. Observations on the evening departure and activity of wintering short-eared owls in New Jersey. Journal of Raptor Research. 23(4): 162-166. [22250] 8. Breining, Greg. 1992. Rising from the bogs. Nature Conservancy. 42(4): 25-29. [19249] 9. Burleigh, Thomas D. 1950. Idaho owls should be pampered, not persecuted; most species aid in controlling small rodents. Idaho Wildlife Review. June/July: 4-5. [21307] 10. California Department of Fish and Game, Natural Diversity Data Base. 1992. Special animals. Sacramento, CA: California Department of Fish and Game, Natural Diversity Data Base. 28 p. [23402] 11. Commonwealth of Masschusetts Division of Fisheries and Wildlife. 1994. Massachusetts list of endangered, threatened, and special concern species. Boston, MA: Natural Heritage and Endangered Species Program, Commonwealth of Massachusetts Division of Fisheries and Wildlife. 23 p. [23006] 12. Clark, Richard J. 1975. A field study of the short-eared owl, Asio flammeus (Pontoppidan), in North America. Wildlife Monograph No. 47. [Place of publication unknown]: The Wildlife Society, Inc. 67 p. [22262] 13. Clark, Richard J.; Ward, James G. 1974. Interspecific competition in two species of open country raptors Circus cyaneus and Asio flammeus. Proceedings, Pennsylvania Academy of Sciences. 48: 79-87. [22375] 14. Detrich, Phillip J. 1989. Effects of water projects on western raptors. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 204-208. [22384] 15. Duebbert, Harold F.; Lokemoen, John T. 1977. Upland nesting of American bitterns, marsh hawks, and short-eared owls. Prairie Naturalist. 9(3/4): 33-40. [22255] 16. Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl. 1988. The birder's handbook: a field guide to the natural history of North American birds. New York: Simon & Schuster, Inc. 785 p. [21559] 17. Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl. 1992. Birds in jeopardy. Stanford, CA: Stanford University Press. 259 p. [23304] 18. Evrard, James O.; Snobl, DeWayne A.; Doeneir, Paul B.; Dechant, Jill A. 1991. Nesting short-eared owls and voles in St. Croix County. Passenger Pigeon. 53(3): 223-226. [22178] 19. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 20. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998] 21. Gould, Gordon I., Jr. 1985. A case for owls. In: Proceedings, 7th annual wildlife conference; 1983 February 4-6; San Francisco, CA. San Francisco, CA: San Francisco Zoological Society: 14-21. [22601] 22. Griffin, Curtice R. 1989. Raptors in the Hawaiian Islands. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. [Place of publication unknown]. National Wildlife Federation: 155-160. [22385] 23. Hoffman, Wayne; Robertson, William B., Jr.; Patty, Paige C. 1979. Short-eared owl on Bush Key, Dry Tortugas, Florida. Florida Field Naturalist. 7(2): 29-30. [22600] 24. Holt, Denver W. 1985. The short-eared owl in Massachusetts. Cape Naturalist. [Brewster, MA: The Cape Cod Museum of Natural History, Inc.]; 14(2): 31-35. [22596] 25. Holt, Denver W.; Melvin, Scott M.; Steele, Brian. 1992. Nestling growth rates of short-eared owls. Wilson Bulletin. 104(2): 326-333. [22177] 26. Hughes, Jeffrey H. 1982. Prey of short-eared owl in southeastern Alaska. Murrelet. 63(1): 22-24. [22253] 27. Johnsgard, Paul A. 1988. North American owls. Washington, DC: Smithsonian Institute Press. 295 p. [23301] 28. Karalus, Karl E.; Eckert, Allan W. 1987. The owls of North America (north of Mexico). [Reprint]. New York: Weathervane Books. [Pages unknown]. [22380] 29. Korpimaki, Erkki; Norrdahl, Kai. 1991. Numerical and functional responses of kestrels, short-eared owls, and long-eared owls to vole densities. Ecology. 72(3): 814-826. [22182] 30. Kruse, Arnold D.; Piehl, James L. 1986. The impact of prescribed burning on ground-nesting birds. In: Clambey, Gary K.; Pemble, Richard H., eds. The prairie: past, present and future: Proceedings, 9th North American prairie conference; 1984 July 29 - August 1; Moorhead, MN. Fargo, ND: Tri-College University Center for Environmental Studies: 153-156. [3561] 31. Kuchler, A. W. 1964. Manual to accompany the map of potential vegetation of the conterminous United States. Special Publication No. 36. New York: American Geographical Society. 77 p. [1384] 32. Lehman, Robert N.; Allendorf, John W. 1989. The effects of fire, fire exclusion and fire management on raptor habitats in the western United States. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 236-244. [22324] 33. Lein, M. Ross; Boxall, Peter C. 1979. Interactions between snowy and short-eared owls in winter. Canadian Field-Naturalist. 93(4): 411-414. [22251] 34. Marr, Thomas G.; McWhirter, Douglas W. 1982. Differential hunting success in a group of short-eared owls. Wilson Bulletin. 94(1): 82-83. [22319] 35. Marti, Carl D.; Marks, Jeffrey S. 1989. Medium-sized owls. In: Proceedings of the western raptor management symposium and workshop; 1987 October 26-28; Boise, ID. Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 124-133. [22382] 36. Maxson, Stephen J.; Herr, Andrea M. 1990. Rough-legged hawk preys on short-eared owl. Loon. 62(2): 108. [22378] 37. Murray, Gale A. 1976. Geographic variation in the clutch sizes of seven owl species. Auk. 93(3): 602-613. [22252] 38. Phillips, Robert L.; Wheeler, Anne H.; Lockhart, J. Michael; [and others]. 1990. Nesting ecology of golden eagles and other raptors in southeastern Montana and northern Wyoming. Fish and Wildlife Technical Report 26. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 13 p. [15474] 39. Ponshair, James F. 1976. Short-eared owls roosting in pine plantation. Jack-Pine Warbler. 54(2): 130-131. [22602] 40. Reynolds, Timothy D. 1978. The response of native vertebrate populations to different land management practices on the Idaho National Engineering Laboratory Site. In: Markham, O. D., ed. Ecological studies on the Idaho National Engineering Laboratory Site: 1978 Progress Report. IDO-12087. Idaho Falls, ID: U.S. Department of Energy, Environmental Sciences Branch, Radiological and Envirnomental Sciences Lab: 171-188. [1961] 41. Reynolds, Timothy D.; Trost, Charles H. 1981. Grazing, crested wheatgrass, and bird populations in southeastern Idaho. Northwest Science. 55(3): 225-234. [1963] 42. Schumeister, Robert P. 1980. Short-eared owl preys on white terns. 'Elepaio. 41(5): 41. [22377] 43. Sinclair, Jim. 1990. Interactions between short-eared owls and northern harriers in Van Buren County. Iowa Bird Life. 60(3): 60-62. [22259] 44. Smith, Ronald A.; Hanebrink, Earl L. 1982. Analysis of regurgitated short-eared owl (Asio flammeus) pellets from the Roth Prairie, Arkansas County, Arkansas. Arkansas Academy of Science Proceedings. 36: 106-108. [22376] 45. Tate, G. Randy; Holt, Denver W.; Melvin, Scott M. 1987. Population dynamics, habitat requirements, and management of short-eared owls on Nantucket. Transactions, Northeast Section of the Wildlife Society. 44: 96. Abstract. [22379] 46. Taylor, Daniel M. 1984. Winter food habits of two sympatric owl species. Murrelet. 65(2): 48-49. [22257] 47. Walley, W. J. 1972. Summer observations of the short-eared owl in the Red River Valley. Prairie Naturalist. 4(2): 39-41. [22261] 48. Wiebe, Karen L. 1991. Food habits of breeding short-eared owls in southwestern British Columbia. Journal of Raptor Research. 25(4): 143-145. [22179] 49. Young, Leonard S. 1989. Effects of agriculture on raptors in the western United States: an overview. In: Proceedings of the western raptor symposium and workshop; 1987 October 26-28; Boise, ID. NWF Scientific and Technical Series No. 12. Washington, DC: National Wildlife Federation: 209-218. [22649] 50. Holt, Denver W. 1993. Trophic niche of nearctic short-eared owls. Wilson Bulletin. 105(3): 497-503. [23537] 51. Herkert, J. R., ed. 1992. Endangered and threatened species of Illinois: status and distribution. Volume 2--Animals. Springfield, IL: Illinois Endangered Species Protection Board. 142 p. [23799] 52. Tate, James, Jr. 1986. The Blue List for 1986. American Birds. 40(2): 227-235. [24324] 53. U.S. Department of the Interior, Fish and Wildlife Service. 1994. Endangered and threatened wildlife and plants; animal candidate review for listing as endangered or threatened species; proposed rule. 50 CFR Part 17. Tuesday, November 15, 1994. Federal Register. 59(219): 58982-59028. [24357]


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