Burrowing owl Speotyto (Athene) cunicularia hypugaea Class: Aves Order: Strigiformes Family: Strigidae Dudek and Associates Species Accounts Status: Federal: Federal Special Concern species; Partners in Flight Priority Bird Species; Fish and Wildlife Service Species of Management Concern State: Species of Special Concern Data Characterization The UCR location database includes approximately 92 records for the western burrowing owl within the planning area dated from 1887 to 1999. Approximately 55 records are relatively recent (within the past 10 years) and of these recent records, 30 are high precision records that can be accurately placed within the area. The habitat types associated with these recent and high precision data records include residential, riparian, grassland, chaparral, alkali playa, and crop lands. The residential habitat records may reflect records that are either no longer extant or where the location is a small pocket of suitable habitat within or adjacent to a developed area. The locations are predominantly recorded for crop land habitats within the planning area. Breeding locations have not been identified within the UCR database. The literature available on the burrowing owl is relatively large. It is focused on the natural history of the species, and also includes physiological studies and management studies including a trapping and relocation protocol. Several general ornithological reference treatments have been prepared for the species and it has been treated within the general raptor literature. A summary of available information as well as proceedings from a symposium (Lincer and Steenhof 1997) provides substantial information for the species, only a small part of which is presented within this species account. Little information is available with respect to the planning area other than general distribution and occurrence information. Habitat and Habitat Associations The burrowing owl occurs in shortgrass prairies, grasslands, lowland scrub, agricultural lands (particularly rangelands), prairies, coastal dunes, desert floors, and some artificial, open areas as a year-long resident (Haug, et al. 1993). They may also use golf courses, cemeteries, road allowances within cities, airports, vacant lots in residential areas and university campuses, fairgrounds, abandoned buildings, and irrigation ditches (Haug, et al. 1993; Hayworth pers. obs.). They may also occur in forb and open shrub stages of pinyon-juniper and ponderosa pine habitats (Zeiner, et al. 1990). They require large open expanses of sparsely vegetated areas on gently rolling or level terrain with an abundance of active small mammal burrows. As a critical habitat feature need, they require the use of rodent or other burrows for roosting and nesting cover. They may also dig their own burrow in soft, friable soil (as found in Florida) and may also use pipes, culverts, and nest boxes where burrows are scarce (Robertson 1929). The mammal burrows are modified and enlarged. One burrow is typically selected for use as the nest, however, satellite burrows are usually found within the immediate vicinity of the nest burrow within the defended territory of the owl. Biogeography The burrowing owl breeds from southern interior British Columbia (nearly extirpated), southern Alberta, southern Saskatchewan (extirpated from a portion of the province), and southern Manitoba (extirpated from a portion of the province), south through eastern Washington, central Oregon, and California to Baja California, east to Western Minnesota, northwestern Iowa, eastern Nebraska, central Kansas, Oklahoma, eastern Texas, and Louisiana, and south to central Mexico. The winter range is much the same as the breeding range, except that most burrowing owls apparently vacate the northern areas of the Great Plains and Great Basin (Haug, et al. 1993). The burrowing owl winters south regularly to El Salvador (e.g., AOU 1998). Zeiner, et al. (1990) describe the distribution, abundance, and seasonality of the burrowing owl within California as follows. It is a year-long resident formerly common in appropriate habitats throughout the state, excluding the humid northwest coastal forests and high mountains. It is present on the larger offshore islands and is found as high as 1,600 m (5,300 ft) in Lassen County. In California, burrowing owls are restricted to the central valley extending from Redding south to the Grapevine, east through the Mojave Desert and west to San Jose, the San Francisco Bay area, the outer coastal foothills area which extend from Monterey south to San Diego and the Sonoran desert (Grinnell and Miller 1944). It is a resident in the open areas of the lowlands over much of the southern California region (Garrett and Dunn 1981). It is greatly reduced in number within the lowlands of Riverside County and appears to be resident within the region although there is some movement of more northerly birds into the southern and coastal parts of the region (Garrett and Dunn 1981). Range Within western Riverside County, the burrowing owl occurs within the central portion within the open lowlands (Garrett and Dunn 1981). It has a sparsely scattered distribution throughout the planning area outside of the montane areas. Breeding and burrow locations have not been identified within the UCR database, although most observations that have been recorded are probably located near a burrow due to the relatively sedentary habits of the species. Key Populations in Planning Area The species has recently been detected east of I-215 on March Air Force Base, the Perris Reservoir area, east of Skinner Reservoir, the upper Menifee Valley, west of the San Jacinto reservoir, along Santa Gertrudis Creek, and within the cities of Corona, Riverside, and Banning (Fish and Wildlife Service, unpublished data; California Science and Engineering Associates 1996). It has also been reported to occur in the Lake Skinner-Domenigoni Valley reserve, Lake Mathews Reserve and the Sycamore Canyon-March ARB Reserve. A focused survey of all suitable areas in the western portion of the county has not been conducted. Observed locations from the U.C. Riverside database tend to be scattered within the central portion of the study area within the more level areas. Other critical colonies are possible between and outside these areas. Biology Genetics: The burrowing owl has been variously placed in the monotypic genus Speotyto or in Athene, where it has three congeners (Haug, et al. 1993). Comparison with other karyotypes in the literature suggests that the burrowing owl should be in a separate genus, Speotyto, as has been done for a number of years although it is frequently still referred to as Athene (Schmutz and Moker 1991).] Diet: The burrowing owl is a crepuscular hunter with a prey base including invertebrates and small vertebrates (Thomsen 1971). They may hunt by using short flights, running along the ground, hovering or by using an elevated perch from where prey is spotted. They are a relatively opportunistic forager (Haug, et al. 1993). Their diet is composed of a variety of foods included Peromyscus, Microtus and beetles. Beetles occur within their diet with more frequency, however, based on biomass, Peromyscus is dominant with Microtus appearing second in overall biomass (Marti 1974). Although they eat mostly insects and small mammals, they also may take reptiles, birds, and carrion. During the breeding season, there are significant declines in the percentage of vertebrate prey in the diet and increases in the invertebrate prey (Haug, et al. 1993). Daily Activity: The burrowing owl is primarily a diurnal species with crepuscular hunting habits (Thomsen 1971). They move the location of the perch to thermoregulate; perch in open sunlight in early morning, and move to shade, or to burrow, when hot (Coulombe 1971). Survival: The minimum annual survival rates in Florida average 68 percent for adult males, 59 percent for adult females and 19 percent for one year old owls (Millsap and Bear 1992). In southern California, the apparent survival rates are 30 percent for juveniles and 81 percent for adults (Thomsen 1971). One banded bird survived to 8 years 8 months (Kennard 1975). Collisions with autos may be a significant cause of mortality (Remsen 1978). Socio-Spatial Behavior: The home range may vary from 0.1 to 4 acres (mean is 2 acres) with an average distance between burrows of 436 feet (Thomsen 1971, Martin 1973). Territory size is directly proportional to the available habitat and burrow availability (Haug et al. 1993). Reproduction: The burrowing owl usually nests in an old burrow of ground squirrel, or other small mammal, and may also use the burrow of badgers and marmots. It may dig its own burrow in soft soil. The Nest chamber is lined with excrement, pellets, debris, grass, feathers; sometimes it is unlined. Pipes, culverts, and nest boxes are used where burrows are scarce (Robertson 1929). The male gives a courtship display and notes in front of the burrow. Breeding occurs from March through August, with a peak in April and May. The clutch size is 6-11, with an average of 7-9 eggs; this clutch size may increase to the north (Bent 1938). The young emerge from the burrow at about two weeks, and they fly by about four weeks (Zarn 1974). Martin (1973) reported 95% of the young fledged, and a mean reproductive success of 4.9 young per pair. The species is semi-colonial; it is probably the most gregarious owl in North America. Nest success was 50 to 57 percent at a site in Oregon with desertion being the major cause of nest failures and typically was related to the proximity to other nesting pairs. Burrow sites with good horizontal visibility and little grass coverage were preferred. Elevated perches were used in habitat with average vegetation height greater than 5 centimeters and not in habitats with vegetation less than 5 centimeters. The elevated perches presumably improved the burrowing owl's ability to detect both predators and prey by increasing their horizontal visibility (Green and Anthony 1989). MacCracken et al. (1985) found that nest burrows were in soils with a greater sand content than non-nest burrows, suggesting that selection for soil type may occur. All nest burrows found to be reused in a study in Oregon were in silty loam (Green 1983). Dispersal: A total of 92 percent of 555 owls that were banded at a nesting area were never re-encountered after the year in which they were banded. The 8 percent that returned to the natal area after being banded, returned one or more years after banding and stayed in the natal area for 2 to 4 breeding seasons (Lutz and Plumpton 1999). Returns of one year old owls were located 2.4 to 26.4 kilometers from the natal nest (Haug, et al. 1993). Threats The threats to the burrowing owl are summarized as: conversion of grassland to agriculture, other habitat destruction, predators, collisions with vehicles, and pesticides/poisoning of ground squirrels (Grinnell and Miller 1944, Zarn 1974, Remsen 1978). A ranking by the resource agencies of the most important threats to the species included loss of habitat, reduced burrow availability due to rodent control, and pesticides (James and Espie 1997). The burrowing owl was formerly common in appropriate habitats throughout the state, excluding the humid northwest coastal forests and high mountains. Population numbers have markedly reduced in recent decades (James and Ethier 1989; Zeiner, et al. 1990). The primary threats to the species include the loss of natural habitat due to urban development and agriculture and the expressed effects of insecticides and rodenticides within occupied habitat. The pesticide Carbofuran has been demonstrated to have negative impacts; Sevin is likely a safer pesticide (Hjertaas, et al. 1995; Blus 1996). The loss of burrowing mammal colonies (due to rodenticides or other means) and the crushing of burrows by heavy equipment and ground maintenance machinery remain problematical. This species is usually associated with flat or shallow slopes on loamy soils; these areas are also attractive to agriculture, as well as residential and industrial development. Shooting losses may be significant (Remsen 1978). The species received official status as Endangered in Canada as of 1986. Burrowing owls have gone from locally common to virtually extirpated in Minnesota in 50 years (Johnsgard 1988). The number of burrowing owl breeding pairs in central western and southern California have drastically declined in the last 50 years; during the 1980's the decline was probably greater than 70 percent (DeSante and Ruhlen 1995). The species appears to be seriously threatened with extirpation from central western and southern California because of the extent and intensity of the development (DeSante and Ruhlen 1995). Special Biological Considerations Physiological ecology studies have shown that the burrowing owl is able to dissipate 135 percent of their heat production by use of pulmocutaneous evaporation facilitated by gular flutter. This allows the species to use areas that may have air temperatures greater than their body temperature. They also were found to have different emissivities of their feathers depending on the season of year. During the winter, the emissivity of the plumage is greater thus allowing them to augment their metabolic heat production with solar radiative heat gain (Coulombe 1970). The importance of retaining colonies must be stressed, as this species appears to have evolved as a colonial species in association with burrowing mammal communities (Dyer 1987). While these owls appear to adapt fairly well to human presence in some cases, i.e., airport runways and other human modified open spaces, the continued presence of active mammal-created burrows is essential. In Oklahoma, the removal of prairie dogs allowed deterioration of burrows, making them unsuitable for nest burrows after one year (Butts 1973). Rodent eradication programs may reduce the consistent availability of high and moderate function habitat. Artificial burrows likely have no long-term viability. The use of insecticides may reduce the availability of their primary prey. Pesticides may have secondary adverse effects through contamination. This is a colonial species; minimum viable colony size for this area is unknown. Remaining habitat is often roadside drainage ditches, increasing potential for significant losses to vehicle collisions (Remsen 1978). Soil type appears to be a factor in nest burrow selection (see Reproduction section above). The burrowing owl was shown to choose moderately to heavily grazed grasslands for nesting and roosting and avoided cultivated fields. Where grassland patches were isolated in cultivation areas, the owls dispersed late, for shorter distances and less often. Mortality rate has been shown to be high in these systems. These changes from pasture to cultivation appear to be resulting in a decline of the species (Clayton and Schmutz 1999). It is also important to determine what type and where within the region owls are selecting burrows before the area is disturbed and before it is decided to provision them with artificial burrows. Burrowing owls produced fewer young when occupying a new burrow, and when using burrows in disturbed areas. They produced more young when using artificial burrows but produced fewer fledglings than natural burrows, thus the actual productivity decreased for the artificial burrows (Botelho and Arrowood 1998). The role of food in limiting the number of offspring fledged from nests has been experimentally investigated in the burrowing owl (Wellicome 1997). Food-supplemented owls laid slightly large clutches and produced eggs of higher volume but did not show higher hatching success or produce more hatchlings than did the unsupplemented birds. Therefore, although food intake may restrict the number of eggs that burrowing owls lay, the total number of young produced at a nest is constrained by food only during the nestling period. Food intake is thus more limiting during brood rearing than during egg laying (Wellicome 1997). Urban sites can act as unintentional preserves and support owl populations if habitat features necessary for owls are provided. This is supported by the documented population at Moffett Field in Santa Clara County California. The population has established itself and is using nest burrows under cement or other hard surfaces. The adult density, number of young fledged or pairs with emergent young is not different at Moffett Field compared to other intentional preserve areas (Trulio 1997). Human activities have had a beneficial effect in Florida where mowing, grazing of cattle and wetland drainage have increased the species' range. Residential and industrial areas currently support the largest concentrations of the species in Florida (Haug, et al. 1993). Because of the intense pressure for urban development within suitable burrowing owl nesting and foraging habitat in California, conflicts between owls and development projects often occur. Owl survival can be adversely affected by disturbance and foraging habitat loss even when impacts to individual birds and nest/burrows are avoided (CDFG 1995). The Staff Report on Burrowing Owl Mitigation (CDFG 1995) outlined the protocol for determining impact assessment. The project site and a 150-meter buffer should be surveyed according to the survey protocol and impacts to the owl should be considered to occur if there is disturbance within 50 meters of a burrow, or there is destruction of natural or artificial burrows, or there is destruction of foraging habitat within 100 meters of a burrow. Mitigation measures should include the provision of 6.5 acres of foraging habitat per pair, provision of two burrows for each burrow impacted, relocation of owls (Trulio 1995), and avoidance of the nesting season. Given the extraordinary, precipitous decline of this species in cismontane southern California (Grinnell and Miller 1944; Sexton and Hunt 1979; Garrett and Dunn 1981; Hamilton and Willick 1996), it cannot be assumed that preferred habitat patches (e.g., dry, level grasslands and open areas with suitable nesting substrates) within the study area continue to accommodate the species in numbers, similar to those in past years (Grinnell and Miller 1944). For instance, this species, fairly common in the Prado Basin and environs as recently as 1986, is now rare at that locale (L. R. Hays, Fish and Wildlife Service, pers. obs.). Focused surveys are needed to determine the present distribution (and abundance) of the species within western Riverside County. The following have been suggested as management strategies (Green 1983): protection of burrowing mammal populations; wood or plastic nest boxes and tunnels; artificial perches which provide hunting and predator observation sites; vegetation management through fire or grazing; and relocation of owls. Other management strategies include: reduce mortality on the breeding grounds, increase productivity, protect and manage the nesting habitat, monitor the populations, manage migration and wintering areas, conduct release programs, and develop public support (Hjertaas 1997). Literature Cited AOU (American Ornithologists' Union). 1998. Check-List of North American Birds. Seventh Edition. American Ornithologists' Union, Washington, D.C. 829 pp. Bent, A. C. 1938. Life histories of North American birds of prey. Part 2. U.S. Natl. Mus. Bull. 170. 482pp. Botelho, E. S. And P. C. Arrowood. 1998. The effect of burrow site use on the reproductive success of a partially migratory population of western burrowing owls (Speotyto cunicularia hypugaea). J. Raptor Research 32: 233-240. Blus, L. J. 1996. Effects of pesticides on owls in North America. J. Raptor Research 30: 198-206. Butts, K. O. 1973. Life history and habitat requirements of burrowing owls in western Oklahoma. Unpublished MS thesis, Oklahoma State University, Stillwater. 188 pp. California Science and Engineering Associates. 1996. Final threatened and endangered species survey, March Air Reserve Base, Riverside County, California. California Department of Fish and Game (CDFG). 1995. Staff Report on Burrowing owl mitigation. State of California. Clayton, K. M and J. K. Schmutz. 1999. Is the decline of burrowing owls, Speotyto cunicularia in prairie Canada linked to changes in the Great Plains ecosystems? Bird Conservation International 9: 163-185. Coulombe, H. N. 1970. Physiological and physical aspects of temperature regulation in the burrowing owl Speotyto cunicularia. Comp. Biochem. Physiol. 35: 307-337. Coulombe, H.N. 1971. Behavior and population ecology of the burrowing owl, Speotyto cunicularia, in the Imperial Valley of California. Condor 73: 162-176. DeSante, D.F. and E.D. Ruhlen. 1995. (draft) A census of burrowing owls in California, 1991-1993. Green, G.A. 1983. Ecology of breeding burrowing owls in the Columbia Basin, Oregon. Unpublished MS thesis, Oregon State University, Corvallis. 51 pp. Garrett, K. and J. Dunn. 1981. Birds of Southern California: Status and Distribution. Los Angeles Audubon Society. 407 pp. Green, G. A. 1983. Ecology of breeding burrowing owls in the Columbia basin, Oregon. M.Sc. Thesis. Oregon State University, Corvallis. Green, G. A., R. G. Anthony. 1989. Nesting success and habitat relationships of burrowing owls in the Columbia Basin, Oregon. Condor 91: 347. Grinnell, J. and A.H. Miller. 1944. The Distribution of the Birds of California. Pacific Coast Avifauna Number 27. Copper Ornithological Club, Berkeley, California. Reprinted by Artemisia Press, Lee Vining, California; April 1986. 617 pp. Hamilton, R. and D.R. Willick. 1996. The Birds of Orange County, California: Status and Distribution. Sea and Sage Press, Irvine, California. 150 pp. with appendices. Haug, E. A., B. A. Millsap, and M. S. Martell. 1993. Burrowing Owl (Speotyto cunicularia). In The Birds of North America, No. 130 (A. Poole and F. Gill, Eds.) . Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists' Union. Hjertaas, D., S. Brechtel, K. De Smet, O. Dyer, E. Haug, G. Holroyd, P. James, and J. Schmutz. 1995. National Recovery Plan for the Burrowing Owl. Report No. 13. Ottawa: Recovery of the Nationally Endangered Wildlife Committee. 33 pp. Hjertaas, D. G. 1997. Recovery plan for the burrowing owl in Canada. Journal of Raptor Research Report 9:107-111. James, P.C., and T.J. Ethier. 1989. Trends in the winter distribution and abundance of burrowing owls in North America. American Birds 43:1224-1225. James, P.C. and R.H.M. Espie. 1997. Current status of the burrowing owl in North America: an agency survey. Journal of Captor Research Report 9:3-5. Kennard, J. H. 1975. Longevity records of North American birds. Bird-banding 46: 55-73. Lincer, J. L., and K. Steenhof . [eds]. 1997. The burrowing owl, its biology and management: including the Proceedings of the First International Symposium. Raptor Research Report Number 9. Lutz, R. S., and D. L. Plumpton. 1999. Philopatry and nest site reuse by burrowing owls: implications for productivity. J. Raptor Research 33: 149-153. MacCracken, J.G., D.W. Uresk, and R.M. Hansen. 1985. Vegetation and soils of burrowing owl nest sites in Conata Basin, South Dakota. Condor 87:152-154. Marti, C. D. 1974. Feeding ecology of four sympatric owls. Condor 76: 45-61. Martin, D. C. 1973. Selected aspects of burrowing owl ecology and behavior. Condor 75: 446-456. Millsap, B. A. and C. Bear. 1992. Double-brooding by Florida Burrowing Owls. Wilson Bull. 102: 313- 317. Pacific Southwest Biological Services. 1991. Western Riverside County Multi-species Habitat Conservation Plan. Robertson, J. M. 1929. Some observations on the feeding habits of the burrowing owl. Condor 31: 38-39. Sexton, C.W. and G.L. Hunt. 1979. An annotated checklist of the birds of Orange County, California. University of California Irvine Museum of Systematic Biology Research Series No. 5. Schmutz, S. M., and J. S. Moker. 1991. A cytogenetic comparison of some North American owl species. Genome 34: 714-717. Remsen, J. V., Jr. 1978. Bird species of special concern in California. Calif. Dep. Fish and Game, Sacramento. Wildl. Manage. Admin. Rep. No. 78-1. 54pp. Thomsen, L. 1971. Behavior and ecology of burrowing owls on the Oakland Municipal airport. Condor 73: 177-192. Trulio, L. A. 1995. Passive relocation: a method to preserve burrowing owls on disturbed sites. J. Field Ornithology 66: 99-106. Trulio, L. 1997. Burrowing owl demography and habitat use at two urban sites in Santa Clara County, California. Journal of Raptor Research Report 9:84-89. Wellicome, T. I. 1997. Reproductive performance of burrowing owls (Speotyto cunicularia): effects of supplemental food. Journal of Raptor Research Report 9: 68-73. Zarn, M. 1974. Burrowing Owl, Report No. 11. Habitat management series for unique or endangered species. Bureau of Land Management, Denver. 25 pp. Zeiner, D. C., W., F. Laudenslayer, Jr., K. E. Mayer, M. White. Editors. 1990. California's Wildlife. Volume 2. Birds. State of California, Department of Fish and Game. Sacramento, California. 731 pp.