Short-eared Owl (Asio flammeus): A Technical Conservation Assessment

Prepared for the USDA Forest Service, Rocky Mountain Region, Species Conservation Project

September 22, 2004

David A. Wiggins, Ph.D. Strix Ecological Research 1515 Classen Drive Oklahoma City, OK 73106

Peer Review Administered by Society for Conservation Biology Wiggins, D. (2004, September 22). Short-eared Owl (Asio flammeus): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/ shortearedowl.pdf [date of access].

ACKNOWLEDGEMENTS

I thank Denver Holt for sending (on short notice) a number of critical publications on short-eared owls, and Karen Wiebe for providing a copy of her unpublished, undergraduate research report. Greg Hayward, Jeff Marks, Carl Marti, and Gary Patton read the entire manuscript and gave many useful tips for enhancing the structure and quality of this assessment.

AUTHOR’S BIOGRAPHY

David Wiggins developed an early interest in ornithology. During his high school years, he worked as a museum assistant under George Sutton at the University of Oklahoma. He later earned degrees from the University of Oklahoma (B.Sc. in Zoology), Brock University (M.Sc.- Parental care in Common Terns, under the supervision of Ralph Morris), and Simon Fraser University (Ph.D. – Selection on life history traits in Tree Swallows, under the supervision of Nico Verbeek). This was followed by a U. S. National Science Foundation Post-doctoral fellowship at Uppsala University in Sweden, where he studied life history evolution in Collared Flycatchers, and later a Fulbright Fellowship working on the reproductive ecology of tits (Paridae) in Namibia and Zimbabwe. He currently splits time between ecological research in Sweden and North America.

COVER PHOTO CREDIT Short-eared Owl (Asio flammeus). Photographed on the Fort Pierre National Grassland, South Dakota, July 16, 2004. ©Terry Sohl (used with permission).

2 3 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF SHORT-EARED OWL

Despite widespread concern over declines in their abundance in many areas of North America, short-eared owls (Asio flammeus) are classified as G5 (secure) by the Nature Conservancy. The population status of this species is difficult to assess because they are nomadic and prone to annual fluctuations in numbers. Consequently, fixed-area census projects such as the Breeding Bird Survey do not adequately sample for short-eared owls. Most recent regional ornithological summaries (including state and provincial bird atlas projects) suggest that declines have occurred across the species’ range, including many areas in Region 2. Short-eared owls appear particularly sensitive to habitat loss and fragmentation, as they require relatively large tracts of grassland and are ground nesters, making them susceptible to the increased predation pressure that is typical within fragmented habitats and near rural developments.

The development of conservation/management plans for short-eared owls has been hampered by the difficulty in accurately assessing their local and regional status, and by a lack of information on reproductive success. Although they are listed as a Bird of Conservation Concern by the U.S. Fish and Wildlife Service, as well as a Priority species within many state and regional Partners in Flight bird conservation plans, no research programs on the conservation status of short-eared owls are currently underway.

The loss of open grassland habitats on the Great Plains and along the Pacific and northern Atlantic coasts has been cited in a number of studies as the primary causative factor behind recent declines in short-eared owls in those areas. On the Great Plains, the primary sources of habitat loss have been the conversion of native prairie to agricultural use and overgrazing of existing grasslands. Along coastal areas, which include many wintering sites, recreational use and land development have caused losses of nearshore marsh and oldfield habitats.

Habitat restoration programs, such as the Conservation and Wetland Reserve Programs, have shown some success in restoring suitable habitat for short-eared owls on private land. Such programs not only provide suitable nesting and wintering habitat, but they may also help to restore small mammal populations, which are the key resource responsible for population fluctuations of owls. However, it is important to note that large blocks of habitat are essential for short-eared owls, and habitat preservation/restoration programs should aim to conserve large blocks of habitat (>100 hectares).

2 3 TABLE OF CONTENTS

ACKNOWLEDGEMENTS...... 2 AUTHOR’S BIOGRAPHY...... 2 COVER PHOTO CREDIT ...... 2 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF SHORT-EARED OWL...... 3 LIST OF TABLES AND FIGURES ...... 5 INTRODUCTION ...... 6 Goal...... 6 Scope and Limitations of Assessment...... 7 Treatment of Uncertainty ...... 7 Publication of Assessments on the World Wide Web...... 7 Peer Review ...... 7 MANAGEMENT STATUS AND NATURAL HISTORY ...... 7 Management Status ...... 7 Existing Regulatory Mechanisms, Management Plans, and Conservation Strategies...... 7 Biology and Ecology...... 8 Systematics...... 8 Distribution and abundance...... 9 Global perspective...... 9 Regional perspective ...... 9 Regional discontinuities in distribution and abundance...... 15 Population trend ...... 15 Activity pattern and movements ...... 17 Habitat ...... 18 Food habits ...... 19 Breeding biology...... 19 Courtship, pair formation, and nest-building ...... 19 Clutch and brood size ...... 20 Parental care and offspring behavior...... 20 Nestling growth ...... 21 Timing of breeding and breeding success ...... 21 Demography...... 21 Genetic characteristics and concerns ...... 21 Life history characteristics ...... 21 Social patterns and spacing ...... 22 Factors limiting population growth ...... 22 Community ecology ...... 22 CONSERVATION...... 24 Threats...... 24 Conservation Status of Short-eared Owl in Region 2 ...... 25 Management of Short-eared Owl in Region 2 ...... 27 Implications and potential conservation elements ...... 27 Tools and practices ...... 28 Inventory and monitoring...... 28 Management practices ...... 28 Information Needs...... 29 REFERENCES ...... 32

EDITOR: Gary Patton, USDA Forest Service, Rocky Mountain Region

4 5 LIST OF TABLES AND FIGURES

Tables: Table 1. Management status of short-eared owls within Region 2 and surrounding states, according to state Partners in Flight bird conservation plans...... 9 Table 2. Short-eared owl population trend results based on North American Breeding Bird Surveys...... 15 Table 3. Clutch size and reproductive success of short-eared owls in North America...... 20 Table 4. Observed and recommended levels of grass structural size classes on four national grasslands in USDA Forest Service Region 2 (Samson et al. 2003)...... 26 Table 5. Summary of management recommendations for short-eared owls on the Great Plains, as proposed by Dechant et al. (2003)...... 29 Table 6. Summary of Partners in Flight management recommendations for short-eared owls within Region 2 and adjacent areas...... 30

Figures: Figure 1. National forests and grasslands within USDA Forest Service Region 2...... 6 Figure 2. Natural Heritage Program designations for short-eared owls in North America...... 8 Figure 3. Range of short-eared owls in North America...... 10 Figure 4. Mean number of short-eared owls observed on Breeding Bird Surveys from 1982 to 1996...... 11 Figure 5. Winter distribution of short-eared owls, based on North American Christmas Bird Count data. .. 12 Figure 6. Patterns of abundance of short-eared owls on annual Christmas Bird Counts (CBC) in Wyoming and Colorado (upper) and South Dakota, Nebraska, and Kansas (lower)...... 14 Figure 7. Modeled potential suitable habitat for short-eared owls in Wyoming and Colorado, based upon GAP analysis...... 16 Figure 8. Envirogram representing the web of linkages between short-eared owls and the ecosystem in which they occur...... 23

4 5 INTRODUCTION owl throughout its range, but with an emphasis on Region 2. This introduction defines the goals of the This assessment is one of many being produced assessment, outlines its scope, and describes the to support the Species Conservation Project for the process used in its production. Rocky Mountain Region (Region 2) USDA Forest Service (USFS). The short-eared owl (Asio flammeus) Goal is the focus of an assessment because it is classified as a sensitive species in Region 2 (see Figure 1 for a map Species conservation assessments produced as of Region 2) and because of its uncertain conservation part of the Species Conservation Project are designed status. In the National Forest System, a sensitive to provide forest managers, biologists, other agencies species is a plant or animal whose population viability and the public with a thorough discussion of the is identified as a concern by a Regional Forester because biology, ecology, conservation, and management of of significant current or predicted downward trends in certain species based on available scientific knowledge. abundance or in habitat capability that would reduce The assessment goals limit the scope of the work to its distribution [FSM 2670.5 (19)]. A sensitive species critical summaries of scientific knowledge, discussion may require special management, so knowledge of its of broad implications of that knowledge, and outlines biology and ecology is crucial. of information needs. The assessment does not seek to develop specific management prescriptions. This assessment addresses the biology, Rather it provides the ecological background upon conservation, and management of the short-eared which management must be based and focuses on the

Figure 1. National forests and grasslands within USDA Forest Service Region 2. 6 7 consequences of changes in the environment that result Publication of Assessments on the from management (i.e., management implications). World Wide Web Furthermore, it cites management recommendations proposed elsewhere and, when these have been To facilitate their use, species conservation implemented, the assessment examines the success of assessments are being published on the Region 2 World their implementation. Wide Web site. Placing the documents on the Web makes them available to USFS biologists and managers, other Scope and Limitations of Assessment agencies and organizations, and the public more rapidly than publishing them as reports. More importantly, it This assessment examines the biology, ecology, facilitates their revision, which will be accomplished conservation, and management of the short-eared owl based on guidelines established by Region 2. with specific reference to the geographic and ecological characteristics of the Rocky Mountain Region. Although Peer Review a majority of the literature on the species originates from field investigations outside the region, to the extent Assessments developed for the Species possible, this document places that literature in the Conservation Project have been peer reviewed prior ecological and social context of the Rocky Mountain to their release on the Web. This report was reviewed Region. Similarly, this assessment is concerned with through a process administered by the Society for reproductive behavior, population dynamics, and other Conservation Biology, employing two recognized characteristics of short-eared owls in the context of the experts on this or related taxa. Peer review was current environment. The evolutionary environment of designed to improve the quality of communication and the species is considered in conducting the synthesis, to increase the rigor of the assessment. but placed in current context.

In producing the assessment, I reviewed refereed MANAGEMENT STATUS AND literature, non-refereed publications, research reports, NATURAL HISTORY and data accumulated by resource management agencies. Management Status Not all publications on short-eared owls are referenced in the assessment, nor were all published materials The short-eared owl was listed as Vulnerable (now considered equally reliable. The assessment emphasizes termed Special Concern) in Canada (COSEWIC 2001) refereed literature because this is the accepted standard based upon a status review in the early 1990s (Cadman in science. Non-refereed publications or reports were and Page 1994). In the United States, the short-eared used when information was otherwise unavailable, but owl is considered a Bird of Conservation Concern both they were regarded with greater skepticism. nationally and within many bird conservation regions by the U.S. Fish and Wildlife Service (USFWS; 2002). Treatment of Uncertainty It is also listed as a Bird of Conservation Concern within USFWS Regions 3, 4, 5 and 6 (including all Science represents a rigorous, systematic of USFS Region 2). Within USFS Region 2, the short- approach to obtaining knowledge. Competing ideas eared owl is listed as a sensitive species. The Bureau of regarding how the world works are measured against Land Management State Director’s Sensitive Species observations. However, because our descriptions of Lists for Colorado (2000) and Wyoming (2001) do not the world are always incomplete and our observations include the short-eared owl. Natural Heritage Program are limited, science focuses on approaches for dealing designations for short-eared owls are shown in Figure with uncertainty. A commonly accepted approach to 2. An overview of these designations reveals that the science is based on a progression of critical experiments short-eared owl currently is viewed as a species at risk to develop strong inference (Platt 1964). However, it throughout most of Region 2. is difficult to conduct experiments that produce clean results in the ecological sciences. Often, we must rely Existing Regulatory Mechanisms, on observations, inference, good thinking, and models Management Plans, and Conservation to guide our understanding of ecological relations. Strategies Confronting uncertainty, then, is not prescriptive. In this assessment, we note the strength of evidence In the United States and Canada, short-eared owls for particular ideas, and we describe alternative are protected from “take” under the Migratory Bird explanations where appropriate. Treaty Act. However, despite evidence of an apparent 6 7 Figure 2. Natural Heritage Program designations short-eared owls in North America (NatureServe Explorer 2003). decline of short-eared owls in North America (e.g., Biology and Ecology Holt 1986, Clayton 2000), there are currently no federal management plans or conservation strategies covering Systematics the species. The species is listed as a Priority Species (in wetlands) in the Colorado (Beidleman 2000) and The short-eared owl is a widespread, nearly Wyoming (Cervoski et al. 2001) Partners in Flight cosmopolitan species, occurring on all continents except (PIF) plans, but PIF plans for other states within Region Australia and Antarctica. The species is considered 2 have not been published. Short-eared owls are also polytypic, with eight or nine subspecies, depending on listed as a Priority and High Priority species in the the source (Mikkola 1983, Cramp 1985, Voous 1988, neighboring states of Montana and Idaho, respectively König et al. 1999). Short-eared owls have colonized (Table 1). A potential problem that has prevented efforts many isolated island groups, and these populations to set conservation strategies for this species is that make up five or six of the recognized subspecies. A short-eared owls are nomadic, breeding and wintering single subspecies (Asio flammeus flammeus) occupies in areas where small mammal (typically Microtus spp.) the entire north-temperate zone (North America, numbers are high. Thus, from year to year, the species Europe, Asia). may go from being relatively common to absent in any particular area. This makes it difficult for local Nominate race: Asio flammeus Pontoppidan. or regional agencies or conservation organizations to accurately characterize the species’ status or to develop coherent management strategies. 8 9 Table 1. Management status of short-eared owls within Region 2 (bolded) and surrounding states, according to state Partners in Flight Bird Conservation Plans. State Status Citation Colorado Priority Species (Wetlands) Beidleman 2000 Kansas State PIF plan not published Wyoming Level I* Priority Species (shortgrass prairie) Cervoski et al. 2001 Nebraska State PIF plan not published South Dakota State PIF plan not published Montana Priority Species (Level III**; Mixed-grass prairie) Casey 2000 New Mexico Not a Priority Species Rustay 2001 Utah Not a Priority Species Parrish et al. 2002 Idaho High Priority Species (Grasslands, wetlands, sagebrush/salt desert shrub) Ritter 2000 Arizona Not a Priority Species Latta et al. 1999 *Level I priority species are those for which urgent conservation action are warranted. **Level III priority species are those of local concern, not in imminent risk or near-obligates for high priority habitat.

Distribution and abundance Regional perspective

Global perspective Historical references generally portray short- eared owls as common breeders on the Great Plains The short-eared owl is a widespread breeding (e.g., see numerous references in Cadman and Page species in the north-temperate and arctic regions, 1994). They were the most common raptor noted southern and northwestern South America, as well as during explorations of the Dakotas in the late 1800s many isolated island groups (e.g., Hawaii, Galapagos, (Allen 1875). In Kansas, they were noted as common Iceland). In North America, they breed in open habitats in the late 1800s (Goss 1886). Although such references throughout most arctic and temperate areas and south must be interpreted cautiously due to the possibility of into the central portions of the United States (Figure observations made during years of peak owl abundance, 3). Short-eared owls are nomadic within their range the general picture drawn from studies on the northern and may be absent from some breeding areas for Great Plains is that short-eared owls were formerly a several years. Note, for example, the large areas of common species. the presumed breeding range on Figure 3 that are not depicted in the map of mean Breeding Bird Survey In Colorado, Sclater (1912) characterized abundance (Figure 4). In addition, there are occasional short-eared owls as winter visitors, and several later breeding records south of the line demarcating publications also mentioned short-eared owls only as wintering and year-round residency. winter visitors and transients (e.g., Aiken and Warren 1914, Niedrach and Rockwell 1939). The lack of Throughout their range, the abundance of documented nesting records in these early studies short-eared owls varies annually, depending on suggests that short-eared owls have never been a local food supplies and habitat conditions. They are common nesting species in Colorado. Ducey (2000) highly nomadic, breeding in areas that support large summarized the results of early expeditions in Nebraska populations of small mammals or other sources of and concluded that short-eared owls were uncommon prey (Holt and Leasure 1993). Populations breeding in there. However, several reports from the northern north-temperate areas abandon their breeding sites and plains suggest that short-eared owls were common in move southward during winter. On the North American the Dakotas. As noted above, Allen (1875) called short- continent, short-eared owls winter mostly south of eared owls the most common raptor on the plains. Several Canada through central Mexico (Figure 3 and Figure early reports list them as common in North Dakota (see 5), where they are often found in small groups, roosting references in Wood 1923, Stewart 1975). Similar claims in areas that provide a high density of Microtus voles or were made in the prairie provinces of Canada (Alberta, other small mammals. This habit of roosting in groups Saskatchewan, Manitoba; Cadman and Page 1994), and is typically referred to as “communal roosting”, and that as far south as Kansas (Goss 1886). terminology will be used elsewhere in this report. 8 9 Figure 3. Range of short-eared owls in North America. The figure is modified from Holt and Leasure (1993).

10 Mean number of short-eared owls observed on Breeding Bird Surveys from 1982 to 1996 (Sauer et al. 2003). Figure 4. Figure

10 Figure 5. Winter distribution of short-eared owls, based on North American Christmas Bird Count (CBC) data. The upper figure represents the average number of short-eared owls counted on CBCs for the period between 1966 and 1996, while the lower figure represents data from the 2002-2003 CBC. Data are from the CBC website (www.audubon.org/bird/cbc). 12 13 More recently, data from Breeding Bird Surveys Wyoming: Both Scott (1994) and Dorn and (BBS; Sauer et al. 2003) and Christmas Bird Counts Dorn (1999) consider short-eared owls as uncommon (CBC; National Audubon Society 2002) show residents, breeding statewide in meadows and statistically significant declines in both breeding and grasslands. Scott (1994) notes that local breeding wintering populations in Region 2 (Figure 6; see the numbers can increase dramatically during periods of Population trend section). Recent breeding bird studies rodent abundance. Knight (1902) also classified short- within Region 2 suggest significant declines in most eared owls as uncommon residents, which suggests that areas (Boyle 1998, Molhoff 2001, Sharpe et al. 2001, the species has always been an uncommon breeder in Busby and Zimmerman 2001, Tallman et al. 2002), with the state. the possible exception of Wyoming (BBS data; Table 2). Thus, the available evidence suggests widespread Nebraska: The Nebraska Breeding Bird Atlas declines in abundance, with subtle shifts in distribution project (1984 to 1989) found only one confirmed (largely westward) on the Great Plains. Currently, nesting in the state over five years, in the southern short-eared owls can be found breeding and wintering panhandle area (Molhoff 2001). Sharpe et al. (2001) throughout low elevation areas of Region 2, but they noted only six nesting records since 1960. Although show strong annual variation in numbers and may be no quantitative evidence is available from historical absent from some areas for several years. Short-eared accounts, Molhoff (2001) and Sharpe et al. (2001), as owls are uncommon, nomadic breeders on the Great well as several earlier reports (Brogie and Mossman Plains south to central and (occasionally) southwestern 1983, Ducey 1988, Blake and Ducey 1991), all suggest Kansas. In Colorado, they are sporadic breeders in that a significant recent (past 50 years) decline in North Park (e.g., Arapaho National Wildlife Refuge abundance has occurred in the state. [NWR]), the San Luis Valley (Alamosa and Monte Vista NWRs), and on the northeastern plains (Figure Colorado: Historically in Colorado, short-eared 7). In Wyoming, they may breed almost anywhere owls were noted primarily in winter, with only a few statewide in low elevation grasslands and marshy areas. reports of nesting (in the southwest and southeast; In all of these areas, numbers can vary strongly from Sclater 1912). However, nesting records slowly year-to-year. For example, there are numerous nesting accumulated during the mid 1900s, and Bailey and records at Arapaho NWR in northcentral Colorado, but Niedrach (1965) noted it as an uncommon resident, few in recent years (Bilbeisi personal communication with most nesting records on the eastern plains. Recent 2003). See Figure 4 for a map of the breeding density breeding records are mostly from the northeastern in North America, based on BBS abundance analyses quarter of the state, along with isolated breeding in (Sauer et al. 2003). North Park (Arapaho NWR), the San Luis River valley (Monte Vista and Alamosa NWRs), and an isolated The historical and current distribution and breeding record in the southwest (Andrews and Righter abundance in Region 2 are as follows: 1992, Boyle 1998). Andrews and Righter (1992) and Boyle (1998) stressed the sporadic nature of nesting South Dakota: Although they gave no indication at specific localities. In general, short-eared owls breed of abundance or breeding records, Over and Thomas and winter in relatively dense grasslands, especially (1921) suggested that short-eared owls occurred those associated with water, but their numbers and statewide but were restricted to prairies and marshes. location vary strongly from year to year. The South Dakota Breeding Bird Atlas (Peterson 1995) reported a total of six confirmed breeding attempts but Kansas: Short-eared owls appear to have noted that records were fewer than expected. In South undergone a drastic decline in abundance as a breeding Dakota, the number of breeding short-eared owls species in Kansas. Goss (1886) considered them a fluctuates strongly among years, depending on local common breeder in the state. Johnston (1964) noted outbreaks of microtine rodents. In 1987 for example, breeding in four eastern counties and classified the 20 pairs were reported breeding on Lacreek NWR in species as an uncommon or low-density resident. southwestern South Dakota (Brashears 1987). Peterson Thompson and Ely (1992) suggested that short-eared (1995) suggested that short-eared owls have declined owls began declining in Kansas in the 1930s and are significantly in South Dakota since 1987, an opinion now very local or absent in the western half of the state that is supported by recent BBS results (see “Population and much reduced in the east. The recent Breeding trends” section). Bird Atlas effort in Kansas (1992 to 1997; Busby and

12 13 0.45 Wyoming and Colorado 0.40 2 0.35 Y = 5.3 - .003 * X; R = 0.18 0.30 0.25 0.20 0.15 Number/hr 0.10 0.05 0.00 -0.05 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

0.45 South Dakota, Nebraska, Kansas 0.40 2 0.35 Y = 6.861 - .003 * X; R = 0.27 0.30 0.25 0.20 0.15 Number/hr 0.10 0.05 0.00 -0.05 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year

Figure 6. Patterns of abundance of short-eared owls on annual Christmas Bird Counts (CBC) in Wyoming and Colorado (upper) and South Dakota, Nebraska, and Kansas (lower). In both cases, the declines were statistically significant (P <0.01). Data were taken from the CBC website http://www.audubon.org/bird/cbc/hr/index.html.

14 15 Table 2. Short-eared owl population trend results based on North American Breeding Bird Surveys. Data were taken from Sauer et al. (2003) and focus on Region 2 (bolded) and surrounding areas. Trend indicates the percentage change per year. For most states within Region 2, there were insufficient data for trend analyses. 1966-1979 1980-2002 1966-2002 Region N Trend P N Trend P N Trend P South Dakota 3 33.2 0.03 5 -11.4 0.00 8 11.1 0.23 Nebraska — — — — — — — — — Wyoming — — — 9 15.2 0.04 10 16.8 0.07 Colorado — — — — — — — — — Kansas — — — — — — — — — North Dakota 9 46.2 0.15 16 13.7 0.23 23 3.4 0.51 Montana 8 -1.9 0.85 18 -12.5 0.00 20 -6.9 0.07 Idaho — — — 9 -3.0 0.53 9 -2.4 0.56 Utah — — — 8 0.4 0.91 8 2.2 0.63 Minnesota — — — 5 38.9 0.45 6 20.3 0.19 Manitoba 2 -6.0 0.83 — — — 7 -34.9 0.02 Saskatchewan 5 -18.7 0.18 — — — 7 -19.8 0.05 Alberta 10 4.0 0.44 13 -12.9 0.05 20 -7.2 0.08 FWS Region 6 22 25.1 0.11 57 -5.0 0.13 72 -2.2 0.34 United States 29 14.8 0.18 99 -4.4 0.03 119 -1.9 0.18 Canada 17 -3.4 0.42 17 -9.3 0.08 34 -12.4 0.00 Survey-wide 46 9.6 0.24 116 -4.9 0.01 153 -4.7 0.00

Zimmerman 2001) found the opposite geographic sporadic breeders in grasslands and marshes throughout pattern, with all five apparent nesting attempts in the the state, but the extent of breeding in the state is not western half of the state. well understood (Scott 1994, Dorn and Dorn 1999).

Within Region 2, the distribution of short-eared The current discontinuity in both abundance and owls does not appear to have changed since the late distribution within the region should not be viewed as 1800s, when the earliest records were kept. However, atypical. Although the breeding distribution was likely at least in the plains states they appear to be much more continuous during the 1800s, when the species more patchily distributed now than in the past, with was more common in the region, even then there would only scattered recent nesting records in most areas. have been strong shifts between years in the density and It is important to note that historical comparisons of location of breeding owls, depending on fluctuating distribution are difficult to make, as the nomadic nature food resources. of the species has complicated nearly every regional account of distribution and abundance. Population trend

Regional discontinuities in distribution and Data from the North American Breeding Bird abundance Survey (Sauer et al. 2003) are summarized in Table 2. Within Region 2, there are so few data that analyses are Short-eared owls are now uncommon to rare hampered due to low statistical power. The only states breeders in a patchy mosaic within South Dakota, with marginally sufficient data are Wyoming and South Nebraska, and Kansas, with annual changes in breeding Dakota. In Wyoming, short-eared owls appear to have locations being the norm. Further west, they appear increased since 1980, while in South Dakota numbers to be more or less a regular breeder (in very small have declined significantly since 1980. It should be numbers) in northeastern Colorado (Boyle 1998), but noted that the combination of BBS methodology not they have only rarely been found nesting in recent years being particularly well-suited to sampling crepuscular at Arapaho NWR (Bilbeisi personal communication species and the very low density of breeding owls 2003). In Wyoming, short-eared owls are uncommon, makes the BBS analyses uncertain. 14 15 Figure 7. Modeled potential suitable habitat for short-eared owls in Wyoming (upper) and Colorado (lower), based upon GAP analysis. The blue circles on the upper figure represent Breeding Bird Survey routes where at least one short-eared owl was observed from 1968 to 1998. The red circles on the lower figure show areas where confirmed breeding activity was recorded during recent Breeding Bird Atlas work in Colorado (Boyle 1998.

16 17 Just outside Region 2, sample sizes from breeding Dakota, Nebraska, Kansas) and mountain (Colorado, bird surveys are more robust. In North Dakota, BBS Wyoming) regions with Region 2 shows statistically data have shown non-significant increases, while in significant declines from 1960 to 2002 (Figure 6), with Montana, there has been a significant decrease (11 the strongest declines having occurred in the 1960s. percent per year) since 1980 (Table 2). The species has Just to the east of Region 2, Breeding Bird Atlas work declined across the prairie provinces of Canada, with in Iowa (1985 to 1990; Jackson et al. 1996) failed to a 13 percent decline per year in Alberta since 1980. confirm nesting in the state during the atlas period. Atlas Declines have been strong in the United States (- 4.4 work in Missouri from 1986 to 1992 found only three percent per year) and in Canada (- 9.3 percent per year) records of confirmed breeding (owls carrying food to since 1980. Overall, the data in Table 2 suggest that young) during the period (Jacobs and Wilson 1995). short-eared owl populations were stable or increasing Although the difficulty in finding short-eared owl nests from 1966 to 1980, but decreasing from 1980 to should be taken into account when assessing Breeding 2002. In fact, BBS analyses of population trends of Bird Atlas records, the relative scarcity of any sightings all North American birds showed that short-eared owls in most of these atlas projects further supports the ranked among the top ten of significant declines (- 4.9 view that short-eared owls are now rare and sporadic percent per year, P = 0.01) over the period from 1980 breeders within Region 2, and in areas to the east and to 2002 (Sauer et al. 2003). Thus, while they must be south of the Region. interpreted cautiously, the available BBS data suggest a serious population decline among short-eared owls in Activity pattern and movements North America. Short-eared owl migratory behavior is poorly Historical references suggest that short-eared owls understood, as relatively few birds have been banded were formerly much more common on the Great Plains and recaptured. Clark (1975) summarized band than they are today. In North Dakota, Stewart (1975) recovery data and found that some birds banded in summarized a number of historical reports, all of which southern British Columbia were later recovered further indicated that the species was common during the 1800s south in Washington, Oregon, and California, while and early 1900s – the more recent decline in numbers others appeared to remain year-round. On the Great was attributed to the conversion of vast tracts of native Plains, one record shows a juvenile banded in North prairie to agricultural use. Janssen (1987) stated that in Dakota and recovered later the same year in eastern Minnesota, short-eared owls have declined dramatically Oregon. One bird banded in the winter in Oklahoma in recent years all across the state. Cultivation of prairie was recovered the following summer in Saskatchewan, in southern Saskatchewan has apparently led to short- and a bird banded in Saskatchewan in summer was eared owls now being rare breeders there, although they shot in southeastern Minnesota three months later remain relatively common in areas of undisturbed, open (Clark 1975). Long distance movements occur; several parkland (Smith 1996). Short-eared owls are currently banding recoveries have shown adults moving >1,500 on the provincial blue list in Alberta, suggesting that km and a juvenile recovered 1384 km away from its they may be at risk (Clayton 2000). BBS data from the natal site (Clark 1975). Northern populations likely three Canadian Prairie provinces confirm that short- are highly migratory, while some southern and coastal eared owls have declined strongly across the region birds may remain in the breeding area year-round (Holt (Table 2). and Leasure 1993). To date, no published records of recoveries of short-eared owls exist for birds banded Recent Breeding Bird Atlas projects in South in Region 2. Dakota (1988 to 1993; Peterson 1995), Nebraska (1984 to 1989; Molhoff 2001), Kansas (1992 to 1997; In Region 2, short-eared owls are present Busby and Zimmerman 2001), and Colorado (1987 to during summer and winter, but whether breeding 1995; Kingery 1998) point out the current scarcity of birds overwinter, or whether they move south and are short-eared owls as a breeding species in the region. replaced by northern birds is not known. This likely These studies found a total of two (South Dakota), depends in part on the local food supply, as short-eared zero (Nebraska), four (Colorado), and five (confirmed owls are highly nomadic and will wander widely in breeding records, Kansas) nests during the respective search of food. atlas periods. Boyle (1998) noted that the Colorado Breeding Bird Atlas study failed to find short-eared Short-eared owls appear to be crepuscular owls at many historical breeding sites in the state. An specialists, foraging most actively at dusk and dawn, analysis of historical CBC data from the plains (South but also at night (Clark 1975). They sometimes forage 16 17 during the day, especially during cloudy conditions. Habitat They forage close to the ground, typically 0.3 to 3 meters high, and either course slowly over an area or In North America, short-eared owls nest in open use a hovering technique (Clark 1975, Village 1987). habitats including grasslands, sagebrush, marshes, Wiebe (1987) found that short-eared owls breeding in and tundra. Recently published nesting records within southwestern British Columbia often used perches as Region 2 suggest that typical habitat is Conservation hunting posts and made 10 of 31 successful captures Reserve Program (CRP) grasslands in Kansas (five from such sites. Clark (1975) found that 21 percent nests; Busby and Zimmerman 2001) and South Dakota of “foraging attempts” were successful, with equal (two nests; Peterson 1995), and inter-mountain and probability of success when coursing vs. hovering. Holt prairie grasslands, as well as marshy areas in Colorado and Leasure (1993) suggested that the foraging period (four nests; Boyle 1998). No recent nesting records was likely determined by a number of factors, including (e.g., Molhoff 2001) exist for Nebraska, but nesting prey density and activity, weather conditions, season, habitat there is likely similar to that in Kansas and and demands of the young. South Dakota. Unpublished nest records from Arapaho NWR in northcentral Colorado show that short-eared Breeding territories vary widely in size, owls sometimes nest in sagebrush areas immediately depending most on local prey abundance (Lockie adjacent to wet meadows and grasslands (Bilbeisi 1955, Clark 1975). In arctic Alaska (Barrow region), personal communication 2003). Descriptions of nest territories averaged 20 hectares (Pitelka et al. 1955a). sites in North Dakota and South Dakota suggested that In coastal Massachusetts, two studies showed mean short-eared owls preferred areas with 30 to 60 cm high territory sizes of 55 and 64 hectares (Holt and Melvin vegetation, in fields with two to eight years of residual 1986, Holt 1992). Clark (1975) found a mean territory vegetation build-up (Duebbert and Lokemoen 1977). size of 82 hectares in Manitoba. In times of food Further east, preferred nesting habitat in Wisconsin abundance, territorial behavior may be relaxed, as Holt was grasslands with maximum vegetation heights of 70 and Leasure (1993) reported 30 active nests within a to 90 cm (28 to 36 inches; Evrard et al. 1991), and in 164 hectare area, while Tate (1992) found 33 nests in Illinois, managed grasslands that were 30 to 40 cm (12 a 200 hectare study area in New Brunswick. Thus, both to 16 inches) tall (Herkert et al. 1999). territorial behavior and territory size largely depend on the prevailing food availability. In other areas of the Great Plains, short-eared owls have been recorded nesting in open grasslands Winter roosts are often stable for several months, along the northern tier of counties in Oklahoma (Texas, but at other times, the number of birds at such roosts Woods, Osage, and Tulsa counties; Nice 1931, Blaha can fluctuate as birds shift sites within a local area et al. 1995, Wilson 1995, Reinking 2004). Although (Clark 1975). The strength of winter site fidelity is recent data from the state are not available, Stewart thought to correlate positively with food abundance, (1975) characterized nesting habitat in North Dakota and negatively with human disturbance (Clark 1975). as native prairie, swales, wet meadows, hayfields, Although owls may defend winter feeding territories, it retired cropland, and fallow stubble fields. Hayward is not clear to what extent such behavior is actually a et al. (1976) described short-eared owl nesting habitat precursor to breeding at such sites (e.g., Clark 1975), or in Utah as marshes and wet pastures. In Minnesota, whether it is a feature common to all wintering areas. short-eared owls have been observed breeding in open, wet prairie in the northwestern part of the state (D. A. The degree to which short-eared owl populations Wiggins, personal observation). In western Montana, on the Great Plains are linked is not known. Adults short-eared owls preferred to nest in ungrazed rather appear to move widely across the Great Plains in search than grazed grasslands (Fondell and Ball 2004). of optimal breeding areas, in response to variation in prey abundance and habitat conditions. More regular Further north, Clark (1975) found that records breeding in the San Luis River valley in southcentral from the Canadian prairie provinces showed that of 63 Colorado suggests that owls may show higher philopatry nests, 55 percent were in grasslands, 24 percent in grain there in response to optimal habitat/prey conditions. stubble, 14 percent in hay fields, and 6 percent in low perennials. The dominant plant at each of 22 nests was cordgrass (at 8 nests), alfalfa (5), spangletop (4), wheat grass (2), sweet clover (2), and bulrush (1).

18 19 Foraging habitat is similar to nesting habitat et al. 1994). In that area, the primary prey from March (see above). No studies have quantified the foraging through October were Microtus voles, which comprised habitat preferences of short-eared owls in North almost half of all prey items identified; secondary prey America. In lieu of such information, foraging habitat included other small mammals such as Northern pocket preferences have typically been inferred from studies gopher (Thomomys talpoides), deer mouse (Peromyscus of nest site selection. maniculatus), and sage vole (Lagurus curtatus). The sage vole declined in abundance from approximately Winter habitat selection has not been carefully 14 percent of the diet in March through July, to being studied in short-eared owls, and most regional completely absent from August through September. As summaries neglect to mention typical winter habitat. In in other studies, non-mammalian prey made up only a Nebraska, Sharpe et al. (2001) described winter habitat fraction of the diet, with only one bird and one beetle as grasslands and marshes. In Oklahoma, preferred among the 233 identified prey remains. Scott (1994) winter habitat appears to be ungrazed or lightly grazed noted that the abundance of short-eared owls increased mid-grass prairie (D. Wiggins, personal observation). dramatically in central Wyoming during a year of Short-eared owls nesting in Grand Teton National Park outbreaks of mice in the sagebrush and grass country. in northwestern Wyoming abandoned breeding sites and Just outside Region 2, pellets collected near nests in were absent in winter (Stone et al. 1994), presumably northeastern Oklahoma consisted of four prairie voles due to heavy snowpack in that area. To the east of (M. ochrogaster), one harvest mouse (Reithrodontomys Region 2, preferred wintering habitat in Missouri has spp.), a least shrew (Cryptotis parva), one horned lark been reported as dense grasslands (Panicum spp. and (Eremophila alpestris), one unidentified bird, and five Aristida spp.), typically less than one foot high (Weller large beetles (Blaha et al. 1995). In Missouri, Weller et al. 1955). et al. (1955) found that the dominant food source of wintering short-eared owls was prairie voles, remains Food habits of which were found in over 95 percent of all pellets collected. These studies suggest that Microtus voles The food habits of short-eared owls have largely comprise the bulk of the short-eared owl’s diet been studied by analyzing the contents of cast pellets throughout the year in Region 2. (e.g., Holt et al. 1987, Blem et al. 1993). Studies from across North America show that short-eared owls feed Breeding biology primarily on small mammals, especially voles (Microtus spp.). Holt and Leasure (1993) summarized a number of Courtship, pair formation, and nest-building studies of short-eared owl prey and found that in most cases, over 98 percent of the prey was comprised of Male short-eared owls may begin courtship small mammals. In addition to Microtus spp., the most displays during the late winter and continue into the common mammalian prey includes shrews (Blarina nesting stage (Pitelka et al. 1955a, Hamerstrom et al. spp., Sorex spp.), pocket gophers (Thomomys spp.), 1961, Clark 1975). These displays usually consist of a moles (Scapanus spp.), rabbits (Sylvilagus spp., Lepus circling upward flight, followed by vocalizations during spp.), and various rodents (e.g., Dipodomys spp., a stoop, and wing-clapping in the vicinity of one or Peromyscus spp.). At coastal study sites, birds can be more females (Clark 1975, Holt and Leasure 1993). an important prey source (Tompkins 1936, Johnston Once the pair bond is established, males may also offer 1956, Holt 1993). Short-eared owls will sometimes females food (courtship feeding), and copulation may specialize on capturing both adult and nestling seabirds follow soon after such feeds (Clark 1975). There is no at coastal sites. Holt (1987, 1994) found remains of information available on the duration of the pair bond. Wilson’s (Oceanodroma oceanicus) and Leach’s storm- petrels (O. leucorhoa) at coastal sites in Massachusetts, On some occasions, the areas used as communal while white terns (Gygis alba) have been taken in roosts during the winter become breeding sites (Holt Hawaii (Schulmeister 1980), and a variety of seabirds and Leasure 1993, Wilson 1995). It is not clear which (especially storm-petrels; Abs et al.1965, Harris 1969) sex chooses the nest site, but apparently only females as well as Darwin’s finches (Grant et al. 1975) are actually construct the nest (Mikkola 1983). Nests are consumed in the Galapagos Islands. typically a simple scrape on the ground, lined by grasses and (occasionally) down feathers, and are placed in The only detailed study of diet within Region 2 relatively low (<0.5 meters) grass, often on a small was carried out just southwest of the Shoshone National knoll or other elevated site (Holt and Leasure 1993). Forest, in Grand Teton National Park, Wyoming (Stone Several studies have noted that short-eared owls will 18 19 sometimes construct a new nest on the remains of the raising older young in the brood. Although short-eared previous year’s nest (Holt and Leasure 1993). owl nestlings sometimes cannibalize younger nestmates during periods of food stress, Holt (1992) noted that In most areas of Region 2, clutches are laid from such behavior may be more appropriately termed mid-April to late May, with a few late records extending scavenging because no actual observations have been into June (Bailey and Niedrach 1965, Tallman et al. made of nestlings killing their nest mates. 2002). Thus, nests with young can be expected from late May until early August. Parental care and offspring behavior

Clutch and brood size As with other aspects of short-eared owl reproductive ecology, parental care patterns have The mean clutch size for short-eared owls in North not been thoroughly quantified. Thus, the following America is 6.9 eggs, with a range of 3 to 11 (Table 3). summary is largely based on casual observations during However, clutch size is highly variable both within and studies involving nesting owls (e.g., Lockie 1955, between localities. Although the factors responsible Pitelka et al. 1955a, b, Clark 1975, Holt 1992). Only for such variation are not currently well understood, female short-eared owls incubate the eggs, beginning it is known that clutch size is higher in years of food once the first egg is laid (Holt and Leasure 1993). abundance (Clark 1975, Holt and Leasure 1993). There During (and just before) the incubation period, the is surprisingly little information on seasonal trends male provides the female with food, but no studies have in clutch size, but this may reflect the general lack of quantified the extent and timing of such feeding. The nesting records within specific localities. Short-eared incubation period has been reported at 21 to 37 days; owls are single brooded, but they will lay a replacement such variability in the estimation of the incubation clutch if the first nesting attempt fails (Clark 1975, Holt period likely relates to variation in the manner in which and Leasure 1993). the period is defined. Females apparently sit tightly on the eggs, especially during periods of food abundance Eggs hatch asynchronously in the order they were (Lockie 1955, Clark 1975). This may be an adaptation laid. The strong hatching asynchrony within broods is to reduce the risk of predation at nests, as eggs are easily thought to be an adaptation to buffer against the effects visible (from above) at untended nests. of an unpredictable food supply. Thus, when food supplies are poor, some young (typically the youngest) At least while the young are small, females do in the brood die, thereby increasing the chances of all the brooding and the actual feeding of the young,

Table 3. Clutch size and reproductive success of short-eared owls in North America. Region 2 states are in bold. Clutch size Study area (n) Range Hatching success Fledging success Citation North/South Dakota 7.0 (13) 4 to 9 100%2 — Deubbert and Lokemoen 1977 Montana 8.1 (29) 6 to 11 74%1 91%1 Holt and Leasure 1993 Montana — — — 60% in ungrazed Fondell and Ball 2004 fields 10% in grazed fields Alberta 6.2 (25) 4 to 10 — — Trann 1974 Manitoba 8.8 (4) 8 to 10 86%1 46%1 Clark 1975 Alaska 6.3 (22) 4 to 8 — 56%3 Pitelka et al. 1955a New Jersey 6.8 (4) — 71%2 — Urner 1925 Massachusetts 5.7 (7) 3 to 8 60%2 37%2 Holt and Melvin 1986 6.2 (9) 4 to 10 76%2 52%2 Holt 1992 Oklahoma 7.0 (2) 6 to 8 0 0 Wilson 1995 1 Percentage of eggs laid that hatched, or percentage of eggs laid that resulted in fledged young. 2 Success was measured by dividing the mean number hatched/fledged by mean clutch size. 3 Percentage of nests where at least one nestling successfully left the nest.

20 21 while the male hunts and provides the majority of the two European studies have shown poor (<50 percent) food to the brooding female (Holt and Leasure 1993). hatching success as a result of predation (see summary The extent to which females hunt for themselves and in Holt and Leasure 1993). Similar interpretation for the young during the nestling period has not been problems exist when assessing fledging success data. quantified. Nestlings often begin dispersing from the In Montana, 91 percent of nestlings (5.5 per nest) nest site before they can fly, at about 14 to 17 days old. successfully left the nest (Holt and Leasure 1993). During this time, they generally stay within 50 meters Elsewhere, fledging success in Manitoba averaged 3.5 of the nest vicinity, remaining quiet and still during the fledglings per nest (Clark 1975), and in Massachusetts day. This pre-fledging dispersal has been viewed as an 2.1 (Holt and Melvin 1986) to 3.2 (Holt 1992) per nest. adaptation to lessen the chances of losing the entire In Montana, reproductive success was 60 percent at brood to nest predators (Holt and Leasure 1993), and it nests in ungrazed grasslands, but it was only 10 percent potentially acts to reduce sibling competition for food in grazed grasslands (Fondell and Bull 2004). (Holt et al. 1992). Young owls eventually fledge (begin flying) at 27 to 36 days of age (Urner 1923, Clark 1975, Demography Holt 1992). After fledging, the young and one or both parents often form a communal roost, and young may Genetic characteristics and concerns roost together with young from other broods (Holt and Leasure 1993). Fledglings are apparently independent Short-eared owls are now relatively rare in of parents one to two weeks after fledging (Urner 1923); Region 2, and their low population density may pose a however, this point needs further study. serious problem for birds that are seeking mates. Short- eared owls are widely distributed in North America, but Nestling growth the actual breeding distribution is more of a mosaic, largely dependent on the local abundance of food and Holt et al. (1992) studied the growth of nestling on habitat conditions. Thus, there are strong grounds to short-eared owls at four nests on Nantucket Island, suspect relatively high gene flow among neighboring Massachusetts. Young owls weigh about 16 grams populations. The fact that wintering birds will at hatching (Clark 1975, Holt et al. 1992) and grow occasionally remain to breed further supports the idea relatively rapidly, gaining about 8 grams per day for the that gene flow is relatively high in this species. Thus, first five days, then 19 grams per day until 10 days old, aside from the species’ increasing rarity, there appears then 21 grams per day until about 15 days old. At this to be little reason for concern over a lack of genetic point, nestlings often leave the immediate nest area, and exchange among birds breeding in and near Region 2. mass gain typically decreases to about 12 grams per day at 16 to 20 days of age. Young owls begin to open their Life history characteristics eyes at five days of age, and feathers begin breaking sheaths at day 9. At day 15, the ear tufts have begun to Short-eared owls may lay large clutches in develop and nestlings are restless, moving around often response to the abundance of prey in the nesting area. on and near the nest. Thus, reproductive potential is high in this species. Individuals are presumed to breed first when they Timing of breeding and breeding success are one year old (Tate 1992), but data on this point are lacking. Although the available data suggest that Short-eared owls are relatively early breeders, pre-fledging survival is relatively high for a ground- laying eggs in April and May throughout Region 2, with nesting species (Table 3), there is little information on late (or re-) nestings in June (Boyle 1998, Sharpe et al. post-fledging survival. No study has measured adult or 2001, Tallman et al. 2002). Hatching success in short- juvenile (from independence) survival rates for short- eared owls is difficult to determine because the fate of eared owls. Given the lack of these critical life history eggs is not always known, nest predators often destroy data, analyses of life cycle diagrams and associated whole clutches during incubation, and different studies demographic matrices (Caswell 1989, McDonald and have not always reported the percentage of eggs laid Caswell 1993) were not carried out in this review. While that hatched. Reported rates of hatching and fledging such analyses can provide valuable insights into which success are in Table 3. A particularly robust data set life-history stages may be most critical to population from Montana showed that of 235 eggs laid, 174 (74 growth, constructing models based on incomplete and/ percent) hatched (Holt and Leasure 1993). Duebbert and or poor quality data may have little relevance (Reed et Lokemoen (1977) reported 100 percent hatching success al. 2002). from 14 clutches in North and South Dakota. However, 20 21 Social patterns and spacing Community ecology

Short-eared owls appear to have a flexible social Interactions between short-eared owls and their system, whereby birds may roost and breed in close predators and competitors, and how these factors proximity when food is abundant, but they are generally interact with habitat use, are shown in an envirogram less gregarious when food abundance and location are in Figure 8. The primary factor affecting owl unpredictable. During the breeding season, territories abundance and breeding success is the availability may be defended strictly (Clark 1975), or birds may nest of grassland and wetland habitats and, indirectly, the in loose aggregations in areas of high prey concentration abundance of small mammal prey. Large patches of (Holt and Leasure 1993). Short-eared owls appear to be open grassland or wetland, ideally in areas away from more gregarious during the winter, with groups of three human developments (sources of disturbance), are to 20 birds sometimes roosting together at relatively necessary for successful breeding and are preferred stable winter roost sites (Holt and Leasure 1993). foraging areas.

Factors limiting population growth Predation of eggs and nestlings can be a significant source of local reproductive failure in short-eared owls The most significant factor thought to limit (Lockie 1955, Pitelka et al. 1955a, Holt and Leasure population growth in short-eared owls is the availability 1993). Known predators of short-eared owl eggs, of suitable nesting and foraging habitat. In Region nestlings, and adults include a number of mammals 2, such habitat is typically composed of large (>500 including red fox (Vulpes vulpes) and striped skunk ha) tracts of native medium to tall grasslands, ideally (Mephitis mephitis). Short-eared owls are also preyed interspersed with wet areas or marshes. Aside from upon by a number of other raptor species, including providing cover for nesting and roosting owls, great horned owl (Bubo virginianus), snowy owl (B. such habitat is also optimal for the small mammal scandiaca), red-tailed hawk (Buteo jamaicensis), populations, especially voles of the genus Microtus. The rough-legged hawk (B. lagopus), northern harrier factors most likely responsible for declines in Region (Circus cyaneus), peregrine falcon (Falco peregrinus), 2 are low reproductive success and poor overwinter northern goshawk (Accipiter gentilis), herring gull survival. The root cause of these problems is likely (Larus argentatus), common raven (Corvus corax), tied to loss and degradation of suitable nesting/foraging and (in Europe) carrion crows (C. corone). Tate (1992) habitat, habitat fragmentation, and consequent decreases also noted that feral cats and dogs may also pose a in prey abundance (see “Conservation” section). The significant threat to short-eared owls. Predation rates situation in western Colorado and western Wyoming is typically increase on ground nesting birds within more difficult to assess because short-eared owls have fragmented habitats (Johnson and Temple 1986). always been uncommon to rare in those areas. However, Consequently, elimination and fragmentation of native the degradation and elimination of shrub-steppe habitats prairie and shrub-steppe habitats in Region 2 have throughout the western United States (Saab and Rich likely led to a significant increase in predation rates at 1997) are likely having a significant negative impact on short-eared owl nests. short-eared owls in the West. Short-eared owls have several competitors for Fluctuations in the abundance of small mammal small mammal prey, with northern harriers occupying prey can also have significant effects on local short- the same habitats and occasionally robbing short- eared owl populations. Short-eared owls are Microtus eared owls of food (Clark 1975). However, Clark and specialists, and because Microtus populations go Ward (1974) proposed that observed breeding and through regular cycles, fluctuations in numbers and wintering sympatry, as well as the lack of close overlap breeding success are a normal aspect of short-eared in preferred prey, are suggestive of little competition owl life history. However, unless compounded by other between the two species. influences (e.g., habitat loss), annual variation in short- eared owl abundance should not be seen as a threat to Holt and Leasure (1993) cited studies reporting population viability. avian tuberculosis (one individual) and fowl cholera (in California) as apparent agents of mortality. The only study of parasites of short-eared owls reported mites (Acarina) from nests in coastal Massachusetts (Philips et al. 1989).

22 RESOURCES nesting/foraging/roosting habitat food: small mammals MALENTITIES competitors: northern harriers disturbance at nests and roosts mortality: collisions with vehicles habitat loss: direct loss of nesting/foraging substrate increased predation at nests habitat degradation: loss of optimal nesting/foraging substrate habitat degradation: reduction in prey abundance increased predation at nests

CENTRUM .

1

absence of draining/agricultural use mowing) occasional disturbance (fire, ungrazed or lightly grazed absence of tilling/agricultural use medium and tall grassland habitat wet grassland, playas small mammals proximity to human settlements agricultural conversion habitat fragmentation livestock grazing

2

wet grassland, playas medium and tall grassland habitat water and soil weather (annual precipitation) open, grassland habitat wet grassland, sloughs, playas open, grassland habitat 3 WEB

4 weather (annual precipitation) water and soil open, grassland habitat water and soil annual precipitation water and soil

Envirogram representing the web of linkages between short-eared owls and ecosystem in which they occur

22 8. Figure grassland habitat CONSERVATION Prairie grasslands on the Great Plains of Canada and the United States were a traditional breeding and Threats wintering area for short-eared owls. Knopf and Samson (1997) assessed agricultural records for the Great Plains Short-eared owls are particularly difficult to track states and found that large proportions of tall, mixed, because they typically shift breeding sites from year to and shortgrass prairie habitats have been converted to year and generally occur at low abundance. BBS data agricultural use. Large-scale conversion of grassland suggest that declines in abundance have occurred since to agricultural purposes has been pointed out as the 1980, with particularly strong declines in the western causal factor behind declines of short-eared owls in the Great Plains (South Dakota, Montana, Alberta). The Canadian prairies (Cadman and Page 1994, Houston primary factors linked to declines of short-eared owls and Schmutz 1999). This lack of suitable grassland have been loss and degradation of habitat (e.g., Holt and habitat may have induced short-eared owls to nest Leasure 1993, Houston and Schmutz 1999, Johnsgard occasionally in agricultural fields, which may represent 2001). Habitat loss and degradation likely affect short- an ecological trap because many such nests fail when eared owls in a number of ways: 1) reducing the overall crops are harvested (Dechant et al. 2003). availability of suitable nesting and foraging habitat, 2) increasing the fragmentation of nesting/foraging habitat, Aside from the direct loss of breeding habitat, 3) increasing predation rates on nests, and 4) decreasing conversion of native habitats also results in increased reproductive success due to lower prey availability. habitat fragmentation, which has several negative consequences. Birds breeding in fragmented habitats Short-eared owls prefer open habitats such are typically more susceptible to nest predation because as grasslands, coastal wetlands, and arctic tundra. habitat fragments contain a greater proportion of edge Holt (1986), Melvin et al. (1989), and Tate (1992) habitats that are favored by predators (Paton 1994, Bock all cited loss of open habitats as the primary factor et al. 1999). In addition, habitat fragmentation may driving declines of short-eared owls. In Massachusetts, have deleterious effects on the prey source (primarily first habitat loss and then increased predation and small mammals) by hindering dispersal and increasing disturbance appear to have driven short-eared owl the overall predation rate. Finally, short-eared owls populations to critically low levels (Holt 1986). In are known to require large blocks of contiguous the northeastern United States, short-eared owls now grassland for nesting, and they also prefer such areas breed primarily on offshore islands (Holt 1986), where for foraging (Holt and Leasure 1993, Dechant et al. habitat conservation has been more of a priority than 2003). Conversion of native grasslands will thereby on the mainland. have strong effects on short-eared owls, relative to most other grassland obligates that can subsist within smaller Conversion of coastal grasslands, marshes, and blocks of habitat. old fields to agricultural, residential, and recreational (e.g., golf courses) purposes has caused a significant loss Short-eared owls prefer relatively tall, dense of habitat in the Fraser River delta of British Columbia, grass for both nesting and foraging, and therefore heavy which historically supported large breeding and wintering livestock grazing may have significant negative effects populations of short-eared owls (Campbell et al. 1990). on local population viability (Bock et al. 1993). Kantrud The number of breeding and wintering birds in the delta and Higgins (1992) found that short-eared owls did not is now much lower than it was historically (Campbell et nest in grasslands that were grazed during the breeding al. 1990, Cooper personal communication 2003). The season. Fondell and Ball (2004) found that short-eared same pattern was noted in Massachusetts (Holt 1986) owls nesting in western Montana preferred ungrazed and is a common factor affecting all coastal areas in grasslands, and that owl reproductive success was southern Canada and the United States. Although such significantly higher in ungrazed plots (60 percent) vs. development has not occurred in arctic areas, populations grazed plots (10 percent. The poor reproductive success there (which are not censused) are also apparently on the in grazed plots was largely due to significantly greater decline. For example, Cadman and Page (1994) showed predation of eggs and nestlings. Given that livestock that the number of birds migrating through southern grazing is a common practice throughout Region 2, areas of Canada has declined significantly in recent and it occurs on private, state, and federal land holdings years. Thus, the widespread loss of coastal wintering (including National Grasslands and National Wildlife areas, as well as the loss of interior prairie and grassland Refuges), Fondell and Ball’s findings suggest that habitats (see below), has contributed to declines in short- livestock grazing may represent a serious threat to eared owl populations. viable populations of short-eared owls. Land managers 24 25 should be encouraged to prevent livestock grazing on land represents suitable breeding habitat for known owl breeding areas during the breeding season short-eared owls is still unclear. (April through July), while limiting grazing at other times of the year. 2. Degradation of existing grasslands due to overgrazing by livestock – This represents Leasure and Holt (1993) reviewed two studies a continuing problem on most land in reporting toxin levels in short-eared owls and concluded Region 2. The CRP may help to reduce this that DDT and DDE residues were not posing a problem problem, given that livestock grazing is for short-eared owl eggshell thickness, for embryonic (with some exceptions) not allowed on CRP mortality, or for tissue damage. However, it should be land. However, livestock grazing on federal pointed out that the two studies (Keith and Gruchy land (e.g., National Grassland, National 1972, Peakall and Kemp 1980) utilized samples from Wildlife Refuges) between April and July is the late 1960s – a new study would provide a good a common practice, and efforts to reduce or comparison for the earlier data. Henny et al. (1984) to eliminate grazing during that period would also found low concentrations of DDE in four of five clearly benefit short-eared owls. sampled short-eared owl eggs in Oregon. 3. Degradation of grassland habitat due to Interactions with competitors and predators are fragmentation – As short-eared owls require thought to have contributed to declines in remnant large (minimum 100 ha) tracts of land populations of short-eared owls in the northeast, as for successful nesting, fragmentation of well as in British Columbia. Melvin et al. (1989) cited grassland habitats has likely had significant predation by skunks as a factor in the decline of owls negative impacts on populations in Region 2. on Martha’s Vineyard, while Holt and Leasure (1993) While it remains a serious problem in Region suggested that overall declines in short-eared owls on 2 (see Knopf and Samson 1997, Samson et Massachusetts’s islands may be the result of a program al. 2004), there remains a clear need to assess to attract barn owls, resulting in direct competition how it is affecting short-eared owls (see the for food. In British Columbia, Campbell et al. (1990) “Information Needs” section). suggested that competition with northern harriers (Circus cyaneus) may have contributed to declines Conservation Status of Short-eared of short-eared owls. However, all of the studies cited Owl in Region 2 above have stressed that the impacts of competition are much less serious than habitat loss and degradation. The breeding distribution of short-eared owls in Region 2 appears to have changed recently. They Short-eared owls were formerly victims of the were formerly widespread breeders in Kansas, widespread negative attitudes about raptorial birds Nebraska, South Dakota, and eastern Colorado, but and were often persecuted by hunters and landowners they are now found in only a few, scattered locations (Townsend 1938). Grinnell and Miller (1944) implicated in western Kansas and the panhandle of Nebraska and shooting by hunters as a factor in the decline of short- in western and central South Dakota. In Colorado, they eared owl populations in California, a view that was are now largely restricted as breeders to three wildlife echoed by Remsen (1978). No recent data are available refuges (Arapaho, Monte Vista, Alamosa NWRs), and on losses of short-eared owls to human persecution on private land along the Platte River valley in the (Holt and Leasure 1993). northeastern quarter of the state. In addition, every Breeding Bird Atlas within Region 2 published in the In summary, the current and historical threats to past 15 years has noted sharp declines in the abundance viable short-eared owl populations in Region 2 can be of short-eared owls. In fact, the Nebraska Breeding ranked as follows: Bird Atlas, which covered the period between 1984 and 1989, reported a total of only six sightings during the six 1. Loss of native grassland and wetland years of fieldwork, and only one “confirmed” breeding habitats – This has been a problem record (Molhoff 2001). The situation in Wyoming historically, but recent efforts (e.g., Playa remains unclear, as no atlas work has been carried out Lakes Joint Venture, Conservation Reserve there and recent short-eared owl nesting records have Program [CRP]) may be slowing habitat not been published. loss. However, the extent to which CRP

24 25 Losses of native grassland in Region 2 states Short-eared owls tend to congregate during have been extreme. Comparing historical with current summer and winter at areas with abundant small estimates, Knopf and Samson (1997) cited an 85 mammal prey. Although the amount of habitat available percent loss of tallgrass prairie in South Dakota, a 98 to owls has declined drastically, that situation may now percent loss of tallgrass and a 77 percent loss of mixed be reversing with programs such as the CRP, which grass prairies in Nebraska, and an 83 percent loss of provides not only idle grassland habitat for owls but may tallgrass prairie in Kansas. More recent estimates, based also benefit small mammal populations by providing on high resolution imagery, suggest a 96 percent loss of more and larger idle grasslands as habitat. While most mixed grass prairie in the northcentral Great Plains (the forms of idle grassland will benefit short-eared owls, area surrounding the Fort Pierre National Grassland in it is important to attempt to convert CRP grasslands South Dakota), a 50 percent loss of mixed grass prairie to native species, rather than the invasive species that in the northwestern Great Plains (including western can typify idle farmland (Samson et al. 2004). Rules South Dakota), and a 75 percent loss of shortgrass for enrolling land in the CRP have recently changed prairie in the Powder River basin (eastern Wyoming, and now strongly encourage (with financial assistance) including Thunder Basin National Grassland). Losses seeding with native grass species, as well as require an in nearby states (e.g., Texas, Minnesota, Missouri) have increase in enrollment period from 10 to 15 years. There typically been even higher (Knopf and Samson 1997). has been a recent increase in the total land enrolled in Thus, much of the original grassland habitat for short- the CRP, and assuming the program is continued in the eared owls in the Great Plains has now been converted future, the long-term program benefits for short-eared to agricultural uses. owls and other grassland species should be good.

The remaining Region 2 native grasslands are Short-eared owls breeding in the sage- often degraded due to heavy grazing pressure (Bock et dominated landscapes of western Colorado and al. 1993). In Region 2, the negative effects of livestock southwestern Wyoming are probably being impacted grazing are likely stronger in mixed and shortgrass by degradation and elimination of sagebrush habitat. prairies, where grazing significantly degrades the However, populations have always been low in such available medium and tallgrass patches and may also landscapes, and it is consequently difficult to assess reduce local prey abundance via habitat destruction. how they have changed recently in response to loss of A recent (1992 to 1998) analysis of existing grassland sagebrush habitat. structural size classes on four Region 2 national grasslands (Table 4) revealed that medium and tall Short-eared owl populations in most of Region 2 classes were significantly underrepresented. Given are at risk because populations have either declined in the the limited amount of prescribed fire carried out on past 20 years, or they are so low that small perturbations these grasslands (see Samson et al. 2003, 2004), the (e.g., poor weather, land-use changes) could lead to lack of tall and medium size classes can be attributed local extirpations. The available evidence suggests that to overgrazing by livestock. Studies of short-eared the primary (historical as well as current) threat to short- owl breeding and foraging habitat selection in various eared owls is the loss of grassland habitat. grazing treatments are clearly needed (see “Information Needs” section).

Table 4. Observed and recommended levels of grass structural size classes on four national grasslands in USDA Forest Service Region 2 (Samson et al. 2003). The recommended size classes given below represent the midpoint of ranges given by Samson et al. (2003). Grass structural size class (percent in class) Short Medium Tall National Grassland Observed Recommended Observed Recommended Observed Recommended

Fort Pierre 32 10 46 40 16 50 Grand River 46 15 23 62 9 23 Buffalo Gap 53 17 24 54 24 29 Ogalala 90 15 8 60 2 25

26 27 Management of Short-eared Owl in reproductive success was extremely poor among those Region 2 pairs that nested in grazed plots.

Implications and potential conservation While providing improved habitat conditions on elements federal lands, such as national grasslands, will certainly improve the situation, restoring native prairie on private Short-eared owls require large expanses of lands has the greatest potential for conserving the short- habitat, ideally a mixture of grassland and associated eared owl. On privately held lands, CRP plots appear wetland. The primary factors affecting the abundance to be an important source of breeding and wintering and reproductive success of short-eared owls in Region habitat for short-eared owls. Further expansion of that 2 are the availability and quality of grasslands and program (in concert with reseeding with native grasses) wetlands. Particularly on the Great Plains, habitat loss, would provide a substantial improvement in habitat fragmentation, and degradation have seriously altered conditions for short-eared owls on the Great Plains. The what was once a large mosaic of native grasslands recent establishment of the Playa Lakes Joint Venture, and wetlands (e.g., playa lakes). Despite apparently expansion of the CRP program to specifically include widespread declines in North American short-eared playa lake wetlands (http://www.fsa.usda.gov/pas/ owl populations, to date very little management or publications/facts/html/nonfloodwet04.htm), and other conservation action has focused on the species. habitat improvement programs (e.g. Wetland Reserve Program, http://www.nrcs.usda.gov/programs/wrp/) are Unfortunately, the relative scarcity of short-eared all likely to result in substantially increased numbers owls together with their nomadic lifestyle has made of short-eared owls on the Great Plains. However, research on the species difficult. Consequently, there is while there is evidence that short-eared owls utilize a critical lack of data concerning the response of short- CRP land for both breeding and wintering in Region eared owls to modifications in habitat. For example, 2 (and elsewhere), the relative success of breeding while limited information is available on the immediate attempts on CRP land is not known. Given that CRP habitat characteristics around individual nests, there is plots often occur in fragmented patterns amid land currently little understanding of the landscape matrix otherwise used for row-crop agriculture, the possibility necessary to support viable populations of short-eared exists that such sites may act as ecological traps, with owls at broader scales. Without knowledge of the birds realizing reduced reproductive success (e.g., due mix of habitat elements necessary (on the landscape to predation) within such plots. Consequently, detailed level) to maintain healthy populations of short-eared studies of the relative reproductive success of owls owls, attempts to formulate management plans will be breeding on CRP (and WRP) lands are needed (see handicapped. Currently, the best available information “Information Needs” section). suggests that increasing the availability of wetlands and ungrazed grasslands will have two benefits for short- In summary, a successful management approach eared owls: 1) increasing the amount of suitable nesting for short-eared owls in Region 2 could best be achieved and foraging habitat, and 2) decreasing the degree to by (in order of importance): which current habitat is fragmented. 1. Improving existing grassland/wetland quality National grasslands within USFS Region 2 by limiting livestock grazing to achieve a contain important remnants of native prairie. However, balanced mix of short/medium/tall grass the available evidence suggests that overgrazing heights. Eliminating or restricting livestock by livestock is a common practice on the national grazing during the owl breeding season grasslands, at least on the northern units in South (April through July) on known or potential Dakota and Nebraska (Table 4; Samson et al. 2003). breeding plots. As short-eared owls prefer medium to tall grasses for foraging and nesting, a grazing regime that more 2. Pursuing habitat conservation measures that accurately represents the assumed historical pattern will increase the amount of native grassland (1/3 short, 1/3 medium, 1/3 tall grasses) would benefit and wetland habitats, particularly on private short-eared owls by increasing the current levels of the land holdings. preferred moderate and tall grasses. A recent study by Fondell and Ball (2004) suggested that short-eared 3. Supporting a research program that would owls prefer to nest in ungrazed grasslands and that monitor the reproductive success of short-

26 27 eared owls within CRP/WRP plots, relative (Leasure and Holt 1991). However, they represent to the success of owls nesting on other land time-consuming efforts and should ideally be carried management types. out once it has been established that owls are nesting locally. Nests are located by dragging light cable chains It is important to note that while points 1 and between two vehicles over suspected nesting areas and 2 above will certainly improve habitat quantity and watching for flushing females (Higgins et al. 1977, quality, a better understanding of short-eared owl Leasure and Holt 1991). Nests are then marked with a demography in relation to landscape level habitat short pole or sapling at least 2 m away from the actual conditions will provide the key information that is nest site, and locations are noted on aerial photographs necessary to formulate a coherent habitat management or detailed maps. Later, when young are approximately plan for the species. 10 days old, females can be captured using a mist net strung between two poles and placed over the nest (see Tools and practices details in Leasure and Holt 1991).

Inventory and monitoring Management practices

The primary problem in attempting to construct No focused conservation work on short-eared a conservation strategy for short-eared owls is that owls is underway within Region 2 or elsewhere. no suitable methods exist for censusing populations. Consequently, aside from some work in the northeastern Because they are largely crepuscular and/or nocturnal, United States in the 1980s (Holt 1986), almost no short-eared owls are poorly sampled with BBS census management tools applicable to short-eared owls have methods, as well as other standard avian survey been developed. Recommendations developed by the methodologies. At the same time, however, because Massachusetts Natural Heritage Program (see Holt and short-eared owls occur in open habitats, surveying Leasure 1993) include: from points of high visibility late in the day may help to establish the species’ local presence. For most areas v developing and implementing a standardized in Region 2, surveys for nesting birds should be carried survey protocol out in May and June. During the breeding season, a basic survey strategy would involve: v maintaining large, continuous tracts of habitat v visual surveys of large areas (180º viewpoints, up to 750 m distant) of potential v monitoring for predators and disturbance grassland habitat (especially wet grasslands) for five minute periods. v creating a public education program

v stops every 1 kilometer (0.6 miles) along a v continuing further research into short-eared transect route. owl ecology.

v observations beginning approximately one Several management techniques may lead to hour before sunset and continuing until improved habitat conditions for short-eared owls in lighting conditions become too poor. Region 2. The best long-term solution is to promote grassland protection through conservation easements, v secondary surveys of the same areas at direct land purchases, and landowner incentive night, with one surveyor using a spotlight programs such as the CRP. Land protection and habitat and the other using binoculars to confirm improvement programs undertaken by the Playa Lakes identification. Joint Venture (www.pljv.org) will have significant positive impacts on short-eared owls in eastern During the non-breeding season, the survey Colorado and western Kansas, as well as wintering areas methods above should be modified to begin under to the south, because this effort is aimed at preserving poorer light conditions, as owls typically are less and recovering playa wetlands throughout the southern crepuscular at that time. Great Plains. Such areas represent prime nesting and wintering habitat for short-eared owls. Methods have been developed to locate short-eared owl nests and to catch nesting females 28 29 Re-seeding idle grasslands (e.g., CRP and WRP with a mosaic of successional stages. The CRP and other fields) with native plants would likely increase small habitat protection schemes have provided a significant mammal populations and improve nesting conditions increase in idle grassland, but attempts should be made for short-eared owls. Native grass reseeding is now a to seed such areas with native grass species rather than requirement on most CRP-enrolled land, and guides fast-growing invasive species. In areas of mixed and to appropriate species are available in most Natural tallgrass prairie (i.e., central and eastern portions of Resources Conservation Service offices. Region 2), prescribed burns at long intervals may help to regenerate habitat. Finally, restriction of livestock As is the case for other grassland bird species grazing on some public lands should be encouraged, in Region 2, the majority of the grassland habitat such that some areas are left ungrazed while others used by short-eared owls has been altered by grazing. are grazed rotationally, thereby establishing higher Although light grazing may improve some grasslands proportions of medium to tall grasses that are preferred in the eastern portions of Region 2, anything other than by owls. light, sporadic grazing will likely have negative effects in the short- and midgrass prairie regions of eastern Several PIF state plans have published Colorado, western Kansas, southeastern Wyoming, management recommendations for short-eared owls and western Nebraska and South Dakota. Samson et al. (Table 6). These plans stress the same management (2003) suggest that historical grazing regimes resulted recommendations as Dechant et al. (2003), but they in grassland structures of 33 percent low (<7.3 cm [2.9 also suggest that programs that promote preservation inches]), 33 percent moderate (7.4 to 9.9 cm [3 to 4 of (primarily) waterfowl habitat (e.g., Wetland Reserve inches]), and 33 percent tall (>10 cm [>4 inches]) size Program) should also be encouraged as short-eared classes on the national grasslands on the northern Great owls will benefit greatly from such work. While such Plains. Given that there is no information available on programs have incidental habitat benefits for many the effects of grazing on short-eared owl reproduction or grassland species, they are particularly beneficial for habitat choice, studies utilizing experimental methods short-eared owls as they preserve optimal owl habitat (with different grazing regimes) would be particularly conditions (grassland/wetland mosaics). The PIF plans insightful (see “Information Needs” section). also stress the importance of delaying mowing until late in the summer (i.e., August), as mowing typically Dechant et al. (2003) summarized the effects of destroys nests when performed earlier in the year. management practices on Great Plains short-eared owl populations, and their recommendations are in Table 5. Information Needs Similar to other authors, Dechant et al. (2003) stressed the primacy of reversing the trend of habitat loss for Short-eared owls often move to new breeding short-eared owls and their prey. Optimal habitat is large sites between years, thereby providing little scope for (>100 hectares) blocks of mixed grass and wetlands, year-to-year continuity in research efforts. Clark (1975)

Table 5. Summary of management recommendations for short-eared owls on the Great Plains, as proposed by Dechant et al. (2003). Recommendations Presumed benefits Create and protect large blocks of grassland and wetlands. Provides optimal habitat for owls and their prey. Preserve native grasslands. Preserve optimal habitat for owls and their prey. Maintain a mosaic of grassland successional stages. Provide for succession of grasslands over time. Use conservation easements, land purchases, and private Provide optimal habitat for owls and their prey. landowner habitat incentive programs to protect habitat. Utilize the Conservation Reserve Program to increase Provide optimal habitat for owls and their prey. grassland habitat. In eastern areas with tallgrass prairie, utilize prescribed burns Regenerate grass to optimal conditions for owls and small every 2 to 5 years. mammals. Increase the amount of public “rangeland” (e.g., national Improve suitability of existing grassland for owls and their grasslands) from which cattle are excluded. prey.

28 29 Table 6. Summary of Partners in Flight management recommendations for short-eared owls within Region 2 and adjacent areas. State Recommendations Presumed benefits Source Wyoming Avoid further fragmentation of existing shortgrass Maintain optimal habitat. Cervoski et al. 2001 prairie. Minimize or eliminate pesticide use in nesting Increase food availability, decrease areas. accumulation of toxins Avoid May to June mowing of hayfields and Decrease loss of eggs and young due grasslands, night mowing, and delay most mowing to mowing. until after 15 July. Control grazing so that a mosaic of grazed and Maintain optimal habitat. ungrazed grassland is available, including climax grasslands. Use conservation easements, land purchases, and Increase available habitat. other grass- and wetland preservation techniques.

Colorado Maintain large tracts of grasslands and wet montane Maintain preferred breeding habitat. Beidleman 2000 meadows. Utilize concurrent waterfowl habitat management Improve/increase habitat for owls work as an indirect source of habitat management for short-eared owls.

Montana Create, manage, and protect large blocks of Maintain/increase preferred breeding Casey 2000 grasslands and associated wetlands (this is of and wintering habitat. primary importance). Manage habitat blocks (on a rotational basis) to Maintain optimal habitat. maintain (dense) nesting cover and adequate habitat for small mammal prey. May include light grazing, late-season mowing, and prescribed burns. Use native seed mixes when reseeding Improve grassland habitat. Conservation Reserve Program lands, preferably in blocks of >100 hectares in size. Discourage mowing of Conservation Reserve Decrease nest losses due to mowing. Program grassland until late summer (August). Discourage sodbusting. Prevent long-term habitat disturbance. summarized the frequency with which short-eared owls is known that short-eared owls are nomadic, the extent bred at various National Wildlife Refuges in the United to which local habitat characteristics (e.g., availability States and found only five sites where they appeared of different grassland successional stages) influence to breed regularly. One of these sites was Monte Vista site fidelity deserves further research. Holt and National Wildlife Refuge in southcentral Colorado. Leasure (1993) suggested that non-cyclic, insular vole Such a regular breeding population may allow for a populations on offshore Massachusetts islands resulted study of a number of problems that are not possible to in greater population stability and higher philopatry study elsewhere. This would include long-term changes there. Thus, it is possible that habitat management in the number of breeding pairs, as well as responses to programs (e.g., wetland inundation schemes, prescribed various management activities (e.g., grazing, prescribed burns) carried out on National Wildlife Refuges may be burns, and water regulation). The apparently higher site providing an optimal mosaic of grassland/wetland cover fidelity (inferred from more regular annual breeding) for short-eared owls, which in turn may be responsible at such sites could be used to study two important for the higher frequency of breeding activity in those demographic traits: survival and philopatry. Although it areas. Studies that involved individually marking 30 31 males and females (e.g., Leasure and Holt 1991) would and mowing. The known management history of such provide conclusive evidence of the extent of site fidelity parcels provides an excellent habitat baseline against at breeding and wintering sites. which owl foraging behavior and breeding attempts could be quantified. Such studies would best be carried Within Region 2, populations of short-eared owls out at more northern sites with Region 2, such as appear to be declining in many areas. The distribution Thunder Basin National Grassland in eastern Wyoming, and size of CRP parcels should be studied to assess Oglala National Grassland in northwestern Nebraska, how important those variables are for breeding and and the Buffalo Gap, Grand River, and Fort Pierre wintering short-eared owls. Although several recent national grasslands in South Dakota. Breeding Bird Atlas efforts in Region 2 have recorded owls breeding on CRP land, reproductive success at A quantitative study of foraging habitat choice, in such sites is not known. Detailed, long-term studies summer and winter, would provide useful information of CRP (and other land set-aside programs) site for the conservation of short-eared owls in Region 2. occupancy and owl reproductive success would help Without such data (e.g., use of grazed vs. ungrazed areas, to clarify the value of such programs for short-eared successional stage, etc..), establishing priority habitats owl conservation. Studies of habitat fragmentation for conservation as well as formulating management (e.g., comparing the abundance and success of owls in plans will necessarily depend on (largely incidental) unfragmented vs. heavily fragmented habitat patches) information taken from studies on nesting habitat. would be particularly useful. In Region 2, the areas that offer the best potential for such studies are in the San Almost all of the substantive studies of short- Luis Valley in southcentral Colorado (Alamosa and eared owl ecology have taken place outside of Region 2, Monte Vista National Wildlife Refuges) as well as the largely in Canada and in Massachusetts. Those studies national grasslands in South Dakota (particularly Fort were cited extensively in this report, but it is important Pierre and Grand River National Grasslands). to note that geographical differences in ecology may exist between birds in Region 2 and those elsewhere in The national grasslands within Region 2 may North America. Consequently, regional studies of the also provide excellent opportunities to assess land type discussed above should be carried out in Region management practices on short-eared owl abundance. 2, preferably at sites where owls are most regular in Land management techniques vary among and within occurrence (e.g., Monte Vista and Alamosa NWRs in the national grasslands, with different parcels receiving southern Colorado, and the Fort Pierre and Grand River different grazing pressures, periodic prescribed burns, national grasslands in South Dakota).

30 31 REFERENCES

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