Current Status, Distribution, and Conservation of the Burrowing Owl (Speotyto Cunicularia) in Midwestern and Western North America

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Current Status, Distribution, and Conservation of the Burrowing Owl (Speotyto cunicularia) in Midwestern and Western North America

Steven R. Sheffield1

Abstract.—The Burrowing Owl (Speotyto cunicularia) inhabits open prairie grassland habitat in the midwestern and western US and Canada. For several years now, numbers of this species in North America have been declining at an alarming rate. Currently, Bur- rowing Owls are listed as endangered in Canada and threatened in Mexico. In the United States, the Burrowing Owl was listed as a Candidate 2 species by the USFWS until 1996, but currently is not formally a listed species. However, Burrowing Owls are listed as either endangered, threatened, or a species of special concern in virtually every state/province in which it occurs in midwestern and western North America. Habitat destruction/alteration, with a subsequent increase in mammalian predation has played a major role in the decline of populations. Exposure to large amounts of pesticides and other human-related disturbances have also played a role in their decline. Burrowing Owls rely on colonial sciurid towns as an integral part of their preferred habitat, but black-tailed prairie dog (Cynomys ludovicianus) populations have been reduced over 98 percent since 1900. These important components of the North American prairie ecosystem are significant and highly coevolved systems where resident species such as Burrowing Owls rely to a significant extent on the other species in the system. I suggest that Burrowing Owls serve as a model sentinel species of the health of the midwestern and western grassland ecosystems and that proactive conservation measures and changes in policy are necessary for the continued existence of populations of Burrowing Owls.

The Burrowing Owl (Speotyto cunicularia) is an conservation status of the Burrowing Owl in inhabitant of the prairie grassland ecosystem of midwestern and western North America. In midwestern and western North America. This addition, a further objective is to review current particular ecosystem is considered by many to conservation measures taken for Burrowing be at greatest risk of human perturbation. Owls and to suggest future research and This species has experienced both local and conservation needs for this species. regional population declines and as a result it is listed in virtually all states and provinces in Populational trends presented here are derived which it occurs. Specifically, the subspecies S. from 30 years of Breeding Bird Count (BBS) c. hypugea, the western Burrowing Owl, is the data (Sauer et al. 1996a) and Christmas Bird taxon of Burrowing Owl listed in midwestern Count (CBC) data (Sauer et al. 1996b). BBS and western North America. data are from 1966-1994 and CBC data are from 1959-1988. Avian population counts The objectives of this paper are to present the such as the BBS and CBC generally are now current population status, distribution, and acknowledged to be useful indicators of pat- terns of avian biogeography and population 1 The Institute of Wildlife and Environmental trends. The BBS and CBC data allow analysis Toxicology, Department of Environmental of distribution and abundance of avian species Toxicology, Clemson University, Pendleton, SC during the breeding season (late spring) and 29670, USA, and National Exposure Research during early winter, respectively. In addition, Laboratory, US Environmental Protection these long-term databases probably are more Agency, Cincinnati, OH 45268, USA. reliable for the highly diurnal and relatively 399 2nd Owl Symposium easy to count Burrowing Owl than for most shown in figure 2. The BBS data indicate that other raptor species. Although these databases there has been an overall decrease of 0.6 are invaluable as tools to estimate population percent/year in Burrowing Owl numbers in numbers and trends, there are certain pitfalls North America and 0.5 percent/year in the US associated with their use (see Butcher 1990 (table 1). For both North America and the US, and Droege 1990 for details on uses of BBS however, the trends from 1966-1979 were a 1.6 and CBC data, respectively). percent and 1.8 percent increase in numbers and the trend from 1980-1994 was a 2.1 POPULATION STATUS/DISTRIBUTION percent and 2.0 percent increase in numbers, respectively. In the Central Region of North The Burrowing Owl occurs from the southern America, there was a 2.8 percent/year decrease portions of western Canada through the west- overall, a 2.3 percent/year increase from 1966- ern United States and Mexico through Central 1979 and 0.5 percent/year decrease from America and into South America south to 1980-1994 (table 1). In this region, significant southern Argentina (Haug et al. 1993). Dis- recent (from 1966-1979 to 1980-1994) declines junct populations occur in Florida and adjacent were seen in North Dakota, New Mexico, Ne- Caribbean Islands. In Canada, Burrowing braska, and Texas (table 1). Significant de- Owls occur in Manitoba, Saskatchewan, clines over shorter periods of time have been Alberta, and British Columbia (fig. 1). In the seen in west-central Kansas, adjacent portions United States, Burrowing Owls occur from of Oklahoma and Nebraska, western portions western Minnesota and Iowa to south to Texas of the Texas panhandle, the Trans-Pecos region and west from Washington through California of Texas, and southern New Mexico (Haug et al. (fig. 1). 1993). Significant increases were seen in Colorado and South Dakota. In the Western Maps of average count and percent change/ Region of North America, there was a 4.6 year for Burrowing Owls from BBS data are percent/year increase overall, a 1.3 percent

Figure 1.—Range map of the Burrowing Owl (Speotyto cunicularia) in North America (map from Haug et al. 1993).

400 Figure 2.—Maps of average count and percent change per year for Burrowing Owls (Speotyto cunicularia) from Breeding Bird Survey data (1966-1994; from Sauer et al. 1996a).

401 2nd Owl Symposium Table 1.—Population trend (percent change/year) based on breeding bird survey data for the Bur- rowing Owl (Speotyto cunicularia) in North America (1966-1994) (Sauer et al. 1996a).

Area Population trend (N)

(1966-1994) (1966-1979) (1980-1994) North America -0.6 (245) +1.6 (121) +2.1 (175) United States -0.5 (238) +1.8 (116) +2.0 (173) Central Region -2.8 (128) +2.3 (66) -0.5 (96) Western Region +4.6 (109)* +1.3 (51) +4.2 (74)* California +5.3 (32)* -2.3 (20) +6.3 (22)* Colorado -3.8 (25) -7.1 (9) +4.7 (23) Nebraska +6.0 (15) +25.5 (8)* -2.0 (10) New Mexico -0.6 (22) -4.1 (6)* -1.6 (18) North Dakota +4.2 (16) +11.2 (8) -9.9 (13)* South Dakota -5.8 (19) +5.6 (15) +10.1 (9) Texas -1.4 (22) +18.9 (14) -8.0 (17)

* = significant population trend increase from 1966-1979 and a 4.2 percent from Mexico indicated that Mexican popula- increase from 1980-1994 (table 1). However, tions were decreasing slightly as well (James data from this region is less complete than that and Ethier 1989). from the Central Region and is made up mainly from California. In this region, significant REASONS FOR DECLINE increases were seen in California. However, it is known that Burrowing Owls were extirpated It is clear that the number one reason for the from British Columbia by 1980 (Haug et al. overall decline of Burrowing Owls is the de- 1993). In California, a survey by DeSante and struction and alteration of their habitat. This Ruhlen (1995) has shown that there has been has come about largely due to development of approximately a 50 percent decline in numbers grasslands into agricultural croplands and in the State over the last 10 years. However, through destruction of prairie dog towns. As significant increases over shorter periods of long ago as the 1930’s, it was recognized that time have been seen in the lower Sonoran intensive cultivation of grasslands and native Desert, lower Colorado River Valley in western prairies was the major factor in declining Arizona and adjacent California, and the Burrowing Owl populations (Bent 1938). Bur- interior valley of California (Haug et al. 1993). rowing Owls strongly prefer open grassland habitat with colonial sciurid populations, and The CBC data are more limited for Burrowing since 1900, black-tailed prairie dog (Cynomys Owls since northern populations move south ludovicianus) populations have been reduced for the winter. Burrowing Owls are known to more than 98 percent. In addition to direct winter primarily in California, Arizona, New destruction of prairie dog towns, the shooting Mexico, Texas, Louisiana, and Florida (fig. 3). of prairie dogs and sylvatic plague have deci- Overall, available data indicate a significant mated prairie dog populations in many areas. decrease of about 0.6 percent/year (table 2). The remaining prairie dog towns are generally California showed a significant decreasing highly fragmented and suboptimal nesting and trend (1.2 percent/year), while Arizona and foraging habitat. This has led to a scarcity of Texas showed slight increasing trends (table 2). suitable nesting burrows for Burrowing Owls in However, overall CBC data for Burrowing Owls many locations, and may reduce chances that suggest a decline in numbers since the mid- unpaired owls will be able to find mates. Habi- 1970’s. A similar analysis of Burrowing Owl tat destruction and alteration has also led to wintering numbers using CBC data found indirect negative impacts on Burrowing Owls, comparable overall trends in numbers in the including an increased frequency of mamma- United States, although analysis including lian predators (White 1994). Such mammalian Florida resulted in a slightly positive overall species as coyotes (Canis latrans), red foxes trend and analysis of the limited CBC data (Vulpes vulpes), gray foxes (Urocyon 402 Figure 3.—Map of winter distribution of Burrowing Owls (Speotyto cunicularia) from Christmas Bird Count data (1959-1988; from Sauer et al. 1996b).

Table 2.—Population trend and abundance contaminants such as anti-cholinesterase based on Christmas bird count data for the (anti-ChE) insecticides has proven to negatively Burrowing Owl (Speotyto cunicularia) in impact Burrowing Owl populations. For ex- North America (1959-1988; from Sauer et al. ample, the carbamate insecticide carbofuran 1996b). was found to result in severe reproductive effects in exposed Canadian Burrowing Owls Area Population Relative (Fox et al. 1989). Anti-coagulant rodenticides trend (N) abundance (e.g., brodifacoum and other second generation (or super warfarin) compounds) and other North America -0.6 (213)* 0.12 types of rodenticides (e.g., strychnine) have Arizona +0.2 (16) 0.10 been shown to cause mortality in many differ- California -1.2 (97)* 0.29 ent owl species, even through the ingestion of Texas +1.2 (52) 0.23 as few as one poisoned prey item (Sheffield 1997). Burrowing Owls located in proximity to * = significant population trend strychnine-coated grain used to control Richardson’s ground squirrels (Spermophilus cinereoargenteus), and badgers (Taxidea taxus) richardsonii) were found to have significantly have increased in numbers in many grassland decreased adult body mass and slightly de- habitats due to the widespread habitat alter- creased breeding success as compared to ation that has tended to modify habitats into control owls (James et al. 1990). Burrowing early successional stages. Owls are known to scavenge dead rodents and other prey items, making them highly suscep- In addition to habitat destruction and alter- tible to secondary poisoning by insecticides and ation, direct mortality due to vehicle collisions rodenticides. and shootings have been important in population declines in some areas (Haug et al. 1993). At least two life history traits of the Burrowing In western Oklahoma, shooting was respon- Owl act to restrict rapid population recovery sible for 66 percent of the known mortality following mortalities. Due to their small body (Butts 1973). Exposure to environmental size and ground nesting habits, Burrowing

403 2nd Owl Symposium Owls are vulnerable to a large number of Table 3.—Conservation status of the Burrowing Owl mammalian, avian, and reptilian predators. (Speotyto cunicularia) in North America by Also, they only produce one brood per year, and country and state/province. will renest only if the first nest is destroyed early in breeding (Haug et al. 1993). State/Province Listing

CONSERVATION STATUS CANADA ENDANGERED Alberta Red List (Endangered) Since 1972, the Burrowing Owl has been British Columbia Red List (Endangered) included on the Blue List, a list intended to Manitoba Endangered provide an early warning of North American Saskatchewan Red List (Endangered) bird species undergoing population or range reductions. During the past decade, the Bur- UNITED STATES NO LISTING1 rowing Owl has been listed as declining (Blue Arizona No listing List; Tate 1986), vulnerable (Jeopardy List; California Species of Special Concern USDI 1991), sensitive (Sensitive List; USDI Colorado Undetermined 1992), federal threatened (Canada, COSEWIC, Idaho Species of Special Concern 1979, 1991), federal candidate 2 species Iowa Endangered (USFWS), and declining (White 1994). The Kansas Species of Special Concern federal candidate 2 species category was offi- Minnesota Endangered cially dropped by the USFWS in late 1996 Montana Species of Special Concern (published in the 5 December 1996 Federal Nebraska Species of Special Concern Register). Currently, the Burrowing Owl has no New Mexico No listing2 formal federal listing in the US, but is included North Dakota Watch (Species of Special Concern) on an informal internal list of former C2 candi- Oklahoma Species of Special Concern date species known as “Species of Concern.” Oregon Species of Special Concern Burrowing Owls are listed as federally endan- South Dakota Species of Special Concern gered in Canada (COSEWIC 1995), and are Texas No listing listed as endangered in the provinces of Utah Species of Special Concern Manitoba, Saskatchewan, Alberta, and British Washington Species of Special Concern Columbia in Canada (table 3). Burrowing Owls Wyoming Candidate 2 Species are listed as a “Species of Special Concern” in almost all of the midwestern and western MEXICO THREATENED states of the United States (table 3). In Mexico, Burrowing Owls were listed as a federally 1 Included on informal federal list of “Species of Concern” threatened (amenazada) species in 1994 2 Included on informal state list of “Species of Special (Secretaria de Desarollo Social de Mexico, Concern” 1994). In addition, Burrowing Owls are a CITES Appendix 2 species, which makes it illegal to transport or trade this species (or have been attempted with mixed results in body parts) across international borders with- British Columbia, Manitoba, and Minnesota. out an appropriate convention export permit. In Canada, a Burrowing Owl recovery plan and a Canadian Burrowing Owl Recovery Team are CONSERVATION MEASURES in place. In the provinces of Manitoba, Saskatchewan, and Alberta, programs to Several innovative approaches have been taken protect private lands from cultivation and in order to conserve Burrowing Owl popula- reseeding practices through lease agreements tions in the United States and Canada. The (both voluntary and monetary) have been use of artificial burrows has allowed the estab- initiated. Another important conservation lishment of small Burrowing Owl colonies and effort for the Burrowing Owl is mandatory allows close study of nest success. Artificial mitigation of developmental impacts in and perches have also been used to provide in- around its colonies. Relocations of Burrowing creased hunting and predator observation Owls have been attempted in California and sites. Pesticide label restrictions now exist for Saskatchewan. Finally, public education carbofuran use in and around Burrowing Owl efforts have been underway in many areas nesting areas in Canada. More drastic conser- throughout the range of the Burrowing Owl. vation efforts such as reintroduction programs For example, Operation Burrowing Owl in 404 Saskatchewan has over 500 members and has 6. Further research and population monitor- acted to protect over 40,000 acres of Burrowing ing is necessary, including the following Owl habitat (Haug et al. 1993). areas: a. Continued monitoring of population CONSERVATION RECOMMENDATIONS numbers and trends is critically important. Volunteer data is highly valuable The Burrowing Owl will require human assis- to this effort. tance if it is to continue to have healthy popu- b. The efficacies of conservation measures lations in North America. Among the conserva- currently in use require study to deter- tion needs of this species are the following: mine what works and what does not work. Currently, there is little quantita- 1. A change of philosophy is required towards tive information available on the suc- prairie dog and ground squirrel towns and cess of various management strategies. grasslands in general—they should not be c. Further development of effective survey looked at as easily developed, weedy or techniques. problem areas but should be actively d. Further analysis of migration and fate conserved as an integral part of the prairie of migratory individuals is badly grassland ecosystem. needed. In particular, it is not known with any certainty where Burrowing 2. Tighter controls should exist over grassland Owls winter in Mexico, Central America, development and disturbances, and mitiga- or South America. We need to ascertain tion of impacts (direct or indirect) should be whether or not there are environmental mandatory. Protection of prairie dog, problems existing in areas occupied by ground squirrel, and selected other burrow- wintering Burrowing Owls. ing mammal populations and their towns e. Continued monitoring and assessment as habitat should be an integral part of of the hazard of secondary poisoning grassland conservation actions. from pesticides (insecticides and rodenticides) is necessary. 3. Continued efforts to control prairie dog and f. The impact of increased mammalian ground squirrel populations in midwestern predators on nesting success of Bur- and western North America are detrimental rowing Owls needs to be determined. to Burrowing Owl populations. Pesticide use in these systems should never occur in CONCLUSIONS the vicinity of active Burrowing Owl nests and all pesticide use should be closely Although listed throughout most of their range monitored for negative impacts on Burrow- in North America, Burrowing Owls continue to ing Owls. undergo mild to relatively severe local and regional population declines. The BBS data 4. The Burrowing Owl should be included as a indicate an overall decreasing trend in North formal candidate species in the United American Burrowing Owls, whereas the CBC States. Further, adding candidate species data indicate a slight overall increasing trend to the list of species receiving recovery in North America, although a significant de- plans and active protection (including crease was seen in California, by far the largest protection of habitat) should be part of the wintering population of Burrowing Owls. Endangered Species Act reauthorization bill Virtually all of the reasons for declines in in the U.S. Burrowing Owl populations still occur throughout most of their range. Habitat destruction 5. The passage of a strong, proactive Endan- and alteration probably account for much of gered Species Act reauthorization bill in the the population decline occurring. Prairie dogs U.S. and a Canadian Endangered Species and ground squirrels continue to be actively Act are crucial to Burrowing Owl conserva- exterminated in many areas of North America, tion. In addition, affording legal protection and prairie grasslands continue to be converted to Burrowing Owls in Mexico is of great for agriculture and other uses. Habitat alter- importance, and efforts should be made to ation may indirectly affect Burrowing Owls coordinate Burrowing Owl conservation through the increase in mammalian nest among North American countries. predators. Vehicle collisions, shooting, and exposure to environmental contaminants may 405 2nd Owl Symposium be significant sources of Burrowing Owl mor- Fox, G.A.; Mineau, P.; Collins, B.; James, P.C. tality in some areas. Many different conserva- 1989. The impact of the insecticide tion measures have been attempted in recent carbofuran (Furadan 480F) on the Burrow- years in order to conserve Burrowing Owl ing Owl in Canada. Tech. Rep. Ser. 72. populations in North America. Burrowing Owls Ottawa, Ontario, Canada: Canadian Wildlife serve as ideal sentinels of the health of the Service. midwestern and western grassland ecosystem. Proactive conservation measures and changes Haug, E.A.; Millsap, B.A.; Martell, M.S. 1993. in land use philosophy and policy are neces- Burrowing Owl. In: Poole, A.; Gill, F., eds. sary for the continued existence of healthy Birds of North America, No. 61. Washing- populations of this species in the grasslands of ton, DC: American Ornithological Union, North America. and Philadelphia, PA: Academy of Natural Sciences. 19 p. ACKNOWLEDGMENTS James, P.C.; Ethier, T.J. 1989. Trends in the I would like to thank Lynne Trulio, Dennis winter distribution and abundance of Flath, Bob Murphy, Jim Belthoff, and Troy Burrowing Owls in North America. Ameri- Wellicome for interesting discussions on Bur- can Birds. 43: 1224-1225. rowing Owls, Geoff Holroyd for providing some information on conservation statuses of Bur- James, P.C.; Fox, G.A.; Ethier, T.J. 1990. Is the rowing Owls, and Paul James for helpful operational use of strychnine to control comments on the manuscript. ground squirrels detrimental to Burrowing Owls? Journal of Raptor Research. 24: 120- LITERATURE CITED 123.

Bent, A.C. 1938. Life histories of North Ameri- Sauer, J.R.; Hines, J.E.; Gough, G.; Thomas, I. can birds of prey. U.S. Nat. Mus. Bull. 170. Peterjohn, B.G. 1996a. The North American breeding bird survey results and analysis Butcher, G.S. 1990. Audubon Christmas bird home page. Version 96.3. Laurel, MD: counts. In: Sauer, J.R.; Droege, S., eds. Patuxent Wildlife Research Center. http: // Survey designs and statistical methods for www.mbr.nbs.gov:80/bbs/. the estimation of avian population trends. U.S. Fish Wildlife Service, Biology Report. Sauer, J.R.; Schwartz, S.; Hoover, B. 1996b. 90(1): 5-13. The Christmas bird count home page. Version 95.1. Center, Laurel, MD: Patuxent Butts, K.O. 1973. Life history and habitat Wildlife Research. http: // requirements of Burrowing Owls in western www.mbr.nbs.gov/bbs/cbc.html. Oklahoma. Stillwater, OK: Oklahoma State University. 188 p. M.S. thesis Secretaria de Desarollo Social de Mexico. 1994. Que determina las especies y subspecies de COSEWIC. 1995. Canadian species at risk. flora y fauna silvestres terrestres y Report of the committee on the status of aquaticas en peligro de extinction, endangered wildlife in Canada. April 1995. amenazadas, raras y sujetas a proteccion 16 p. especial, y que estableces especificationes para su proteccion. Norma Oficial Mexicana DeSante, D.F.; Ruhlen, E. 1995. A census of NON-059-ECOL-1994. Diario de la Burrowing Owls in California, 1991-1993. Federacion, Mexico, 487: 2-60. Point Reyes Station, CA: Institute for Bird Populations, Sheffield, S.R. 1997. Owls as biomonitors of environmental health hazards. In: Duncan, Droege, S. 1990. The North American breeding J.R.; Johnson, D.H.; Nicholls, T.H., eds. bird survey. In: Sauer, J.R.; Droege, S., eds. Biology and conservation of owls of the Survey designs and statistical methods for northern hemisphere: 2d international the estimation of avian population trends. symposium; 1997 February 5-9; Winnipeg, U.S. Fish Wildlife Service, Biology Report. Manitoba. Gen. Tech. Rep. NC-190. St. 90(1): 1-4. Paul, MN: U.S. Department of Agriculture,

406 Forest Service, North Central Forest Experi- U.S. Department of Interior. 1992. Endangered ment Station: 383-398. and threatened wildlife and plants. 50 CFR 17.11 & 17.12, 29 Aug. 1992. Tate, J., Jr. 1986. The blue list for 1986. American Birds. 40: 227-236. White, C.M. 1994. Population trends and current status of selected western raptors. U.S. Department of Interior. 1991. Endangered Studies in Avian Biology. 15: 161-172. and threatened wildlife and plants; animal candidate review for listing, proposed rule: Part VIII. Federal Register 56:58804-58836.

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