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2007 Conservation of grassland birds in North America: understanding ecological processes in different regions Robert A. Askins Connecticut College, [email protected]

Felipe Chávez-Ramírez

Brenda C. Dale

Carola A. Haas Virginia Polytechnic Institute and State University

James R. Herkert

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Recommended Citation Askins, R. A., F. Chávez-Ramírez, B. C. Dale, C. A. Haas, J. R. Herkert, F. L. Knopf, and P. D. Vickery. 2007. Conservation of grassland birds in North America: understanding ecological processes in different regions. Ornithological Monographs 64:1-46.

This Article is brought to you for free and open access by the Biology Department at Digital Commons @ Connecticut College. It has been accepted for inclusion in Biology Faculty Publications by an authorized administrator of Digital Commons @ Connecticut College. For more information, please contact [email protected]. The views expressed in this paper are solely those of the author. Authors Robert A. Askins, Felipe Chávez-Ramírez, Brenda C. Dale, Carola A. Haas, James R. Herkert, Fritz L. Knopf, and Peter D. Vickery

This article is available at Digital Commons @ Connecticut College: http://digitalcommons.conncoll.edu/biofacpub/1 Conservation of Grassland Birds in North America: Understanding Ecological Processes in Different Regions Author(s): Robert A.AskinsFelipeChávez-RamírezBrenda C.DaleCarola A.HaasJames R.HerkertFritz L.KnopfPeter D.Vickery Source: Ornithological Monographs No. 64:1-46. 2007. Published By: The American Ornithologists' Union DOI: http://dx.doi.org/10.1525/0078-6594(2007)64[1:COGBIN]2.0.CO;2 URL: http://www.bioone.org/doi/full/10.1525/0078-6594%282007%2964%5B1%3ACOGBIN %5D2.0.CO%3B2

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BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Ornithological Monographs Volume (2007), No. 64, 1–46 © The American Ornithologists’ Union, 2007. Printed in USA. CONSERVATION OF GRASSLAND BIRDS IN NORTH AMERICA: UNDERSTANDING ECOLOGICAL PROCESSES IN DIFFERENT REGIONS Report of the AOU Committ ee on Conservation Robert A. Askins,1,8 Felipe Chávez-Ramírez,2 Brenda C. Dale,3 Carola A. Haas,4 James R. Herkert,5 Fritz L. Knopf,6,9 and Peter D. Vickery7 1Department of Biology, Connecticut College, New London, Connecticut 06320, USA; 2Platt e River Whooping Crane Trust, 6611 West Whooping Crane Drive, Wood River, Nebraska 68883, USA; 3Canadian Wildlife Service, 200–4999 98th Avenue, Edmonton, Alberta T6B 2X3, Canada; 4Department of Fisheries and Wildlife Sciences, MC 0321, Virginia Tech, Blacksburg, Virginia 24061, USA; 5The Nature Conservancy, 301 S.W. Adams Street, Suite 1007, Peoria, Illinois 61602, USA; 6713 Boulder Circle, Fort Collins, Colorado 80524, USA; and 7Center for Ecological Research, P. O. Box 127, Richmond, Maine 04357, USA

Abstract.—Many species of birds that depend on grassland or savanna habitats have shown substantial overall population declines in North America. To understand the causes of these declines, we examined the habitat requirements of birds in six types of grassland in diff erent regions of the continent. Open habitats were originally maintained by ecological drivers (con- tinual and pervasive ecological processes) such as drought, grazing, and fi re in tallgrass prairie, mixed-grass prairie, shortgrass prairie, desert grassland, and longleaf pine savanna. By contrast, grasslands were created by occasional disturbances (e.g., fi res or beaver [Castor canadensis] activity) in much of northeastern North America. The relative importance of particular drivers or disturbances diff ered among regions. Keystone mammal species—grazers such as prairie-dogs (Cynomys spp.) and bison (Bison bison) in western prairies, and dam-building beavers in eastern deciduous forests—played a crucial, and frequently unappreciated, role in maintaining many grassland systems. Although fi re was important in preventing invasion of woody plants in the tallgrass and moist mixed prairies, grazing played a more important role in maintaining the typi- cal grassland vegetation of shortgrass prairies and desert grasslands. Heavy grazing by prairie- dogs or bison created a low “grazing lawn” that is the preferred habitat for many grassland bird species that are restricted to the shortgrass prairie and desert grasslands. Ultimately, many species of grassland birds are vulnerable because people destroyed their breeding, migratory, and wintering habitat, either directly by converting it to farmland and building lots, or indirectly by modifying grazing patt erns, suppressing fi res, or interfering with other ecological processes that originally sustained open grassland. Understanding the ecological processes that originally maintained grassland systems is critically important for eff orts to improve, restore, or create habitat for grassland birds and other grassland organ- isms. Consequently, preservation of large areas of natural or seminatural grassland, where these processes can be studied and core populations of grassland birds can fl ourish, should be a high priority. However, some grassland birds now primarily depend on artifi cial habitats that are managed to maximize production of livestock, timber, or other products. With a sound understanding of the habitat requirements of grassland birds and the processes that originally shaped their habitats, it should be possible to manage populations sustainably on “working land” such as catt le ranches, farms, and pine plantations. Proper management of private land will be critical for preserving adequate breeding, migratory, and winter habitat for grassland and savanna species. Received 12 December 2006, accepted 24 April 2007.

Resumen.—Muchas especies de aves que dependen de habitats de pastizal o savana han mostrado disminuciones signifi cativas en sus poblaciones en Norte America. Para poder entender las causas de estas disminuciones examinamos los requerimientos de habitat de aves

8E-mail: [email protected]. Coauthors are listed alphabetically. 9U.S. Department of Interior (retired). 1 2 ORNITHOLOGICAL MONOGRAPHS NO. 64

en seis regiones del continente. Habitats abiertos originalmente se mantenían por conductores ecológicos (procesos ecológicos continuos y perdurables), como sequía, pastoreo, y/o fuego como en praderas de pastizal alto, mediano, y corto, pastizal desértico y sabana de pino de hoja larga. En contraste, los pastizales se crearon por disturbios ocasionales (fuego o actividad de castores) en el noreste de Norte America. Especies claves de mamíferos (como perrito de las praderas y bisonte en las praderas del oeste y castores en bosque deciduos del este) jugaron un papel cru- cial, y frecuentemente no apreciado, manteniendo sistemas de pastizales. Mientras el fuego fue importante en prevenir la invasión de especies leñosas en praderas de pastizal alto y mediano, el pastoreo jugo un papel mas importante en mantener la vegetación típica de pastizales cortos y desérticos. Alta presión de pastoreo por perrito de las praderas y bisontes crearon una capa de “césped pastoreado” que es el habitat preferido por algunas especies de aves de pastizal que están restringidas a las Grandes Planicies y pastizales desérticos. Muchas especies de aves de pastizal estan vulnerables porque la actividad humana ha destru- ido sus habitats de anidacion, migración e invernacion directamente mediante la conversión a áreas de cultivo o construcción, o indirectamente mediante la modifi cación de patrones de pastoreo, supresión de fuego, o interfi riendo con otros procesos ecológicos que originalmente mantenían el pastizal abierto. El entendimiento de los procesos ecológicos que mantenían el sistema de pastizal es sumamente importante para esfuerzos de mejoramiento, restauración, o creación de habitats para aves de pastizal y otros organismos. Consecuentemente, de alta prio- ridad debería de ser la preservación de grandes áreas de pastizal natural o seminatural donde estos procesos se podrían estudiar. Sin embargo, muchas especies de pastizal ahora dependen principalmente de habitats artifi ciales manejados para maximizar la producción de ganado, madera, u otros productos. Con un claro entendimiento de los requerimientos de habitat de aves de pastizal y los procesos que originalmente moldearon sus habitats seria posible man- tener sus poblaciones en terrenos manejados como ranchos ganaderos, granjas, y plantaciones de pino. El manejo apropiado de tierras privadas será critico para la preservación adecuada de areas de habitat de anidacion, migración e invernacion para aves de pastizal y savana.

Bird species that depend on grassland and of the farmland that dominated the landscape shrubland have declined in many regions in in the 18th and 19th centuries (Norment 2002), eastern and central North America during the but also in the Midwest (Herkert 1995) and the past century, and open-country species fre- Great Plains (Knopf 1994), the historical centers quently outnumber woodland species on state of abundance and diversity of grassland birds. lists of endangered and threatened species Population declines have also occurred in (Askins 1993). Grassland birds, in particular, grassland birds in South America (Vickery et al. appear to be in trouble; during the past 25 years 1999b), Europe (Newton 1998), and other parts they have shown “steeper, more consistent, of the world (Goriup 1988). and more geographically widespread declines Although declines in particular grassland than any other behavioral or ecological guild” bird populations can be att ributed to a wide of North American birds (Knopf 1994:251). An variety of factors, such as habitat fragmenta- analysis of continent-wide population trends tion, nest parasitism, pesticides, and invasion on Breeding Bird Survey (BBS) routes between by woody vegetation (Peterjohn and Sauer 1966 and 2002 showed that only 3 of 28 species 1999), an overriding cause of regional declines of grassland specialists increased signifi cantly, appears to be agricultural intensifi cation. whereas 17 species decreased signifi cantly Because most natural grasslands were con- (Sauer et al. 2003). Although some species that verted to farmland or are used as ranchland, showed a continent-wide population decline grassland birds now largely depend on habitats were increasing in particular regions, many that are managed for agricultural production. species (including Bobolink [Dolichonyx ory- Although farmland and pasture may provide zivorus] and Eastern Meadowlark [Sturnella good breeding or wintering habitat for some magna]) declined throughout almost their grassland bird species (e.g., Wunder and Knopf entire breeding range. Population declines 2003), their suitability oft en declines as agricul- of grassland birds have occurred not only in ture becomes more effi cient. Agricultural inten- the northeastern United States (Vickery 1992), sifi cation involves a shift toward monocultures where regenerating forest has replaced much that support fewer natural species (Matson et CONSERVATION OF GRASSLAND BIRDS 3 al. 1997), and the channeling of more primary Scope of this Paper production toward food or fi ber. In a broad sense, intensifi cation would include conver- We have decided to defi ne grassland birds sion of rangeland to cropland, and the shift to broadly, following Vickery et al. (1999b:5): “any the use of exotic grasses and forbs in pastures species that has become adapted to and reliant and hay meadows. A suite of factors associated on some variety of grassland habitat for part with agricultural intensifi cation tend to degrade or all of its life cycle.” We include species that grassland bird habitat: these include increased use the grass stratum of open savanna habitats, use of pesticides, removal of natural fi eld edges, such as the longleaf pine savannas of the south- spring plowing, land drainage, replacement eastern United States or oak savannas on the of mixed farms with farms dominated by one edge of the tallgrass prairie. crop, harvesting or mowing earlier in the season Because we surveyed such a wide range when birds are still nesting, and higher stock- of grassland habitats, we att empted to use ing rates for livestock (Newton 1998). Murphy ecological terms precisely and consistently (2003) showed that population changes in to improve clarity. In regions where the grassland birds in eastern and central North dominant vegetation is forest, grassland America between 1980 and 1998 were highly ecologists emphasize the “disturbances” that correlated with changes in agricultural land remove woody plants to create and sustain use in their breeding areas. The most important grassland. They emphasize the importance of factor was loss of rangeland, which was asso- understanding the frequency, seasonality, and ciated with negative population trends for 12 intensity of disturbances, and the size of dis- species of grassland birds. Rangeland is used turbance patches. In prairie regions, where the for livestock production, but it generally is not dominant vegetation was originally grass, this managed as intensively as cropland or pasture terminology does not work well. The grassland and it is dominated by native species of plants, was sustained by frequent or even continual providing habitat for a diverse group of grass- processes such as drought, fi re, and grazing, land birds (Peterjohn 2003). In the Midwest, and prairie ecologists emphasize that the real population declines in several species of grass- “disturbance” was removing or modifying land birds are highly correlated with declines in these processes (Evans et al. 1989). These more the combined area of pasture and hay meadow continual and pervasive ecological processes (Herkert et al. 1996). are called “ecological drivers” by prairie ecolo- Our goal is to provide recommendations for gists. We use the term “driver” for ecological halting and reversing the decline in grassland processes that are continual and pervasive and birds. In some cases, this may be accomplished the term “disturbance” for ecological events by restoring natural grasslands, but in other cases that are infrequent and episodic. We recog- it is more realistic to try to promote farming and nize that there is a gradient from continual to ranching methods that make the land both eco- highly infrequent processes, so this distinction nomically productive and biologically diverse. is not always clear-cut. In either case, it is important to understand the For each region, we describe the history and ecological processes that sustained grassland status of grassland birds and their habitats. This habitat before people began to modify the land- is not intended as a comprehensive review of scape. Here, we explore the main ecological pro- the ecology of grassland birds in each region, cesses that sustained grassland in several distinct however. Instead, we focus on the dominant regions of temperate North America. Instead of ecological disturbances or drivers that sustained att empting to survey every type of grassland, the most widespread types of grassland and we focus on some of the most widespread or savanna before European sett lement, includ- well-studied systems to illustrate the relative ing a consideration of the extent to which these importance of diff erent ecological processes processes have been suppressed and replaced in diff erent regions. The general conclusions with artifi cial processes that sustain grassland. derived from this analysis should be applicable Our goal is to show how understanding the to other grassland systems in North America and original ecological processes in a region can aid in other parts of the world where the biodiversity eff orts to maintain or restore grassland habitat of grassland organisms is declining. for birds. 4 ORNITHOLOGICAL MONOGRAPHS NO. 64

Northeastern Grasslands from hurricanes and other storms, tree diseases, and damage from infestations of insects such History of grasslands.—Before European set- as spruce budworm (Choristoneura fumiferana) tlement, grasslands in temperate northeastern also helped create conditions that were favor- North America (defi ned as Pennsylvania, Ohio, able for extensive and intense fi res that would New York, New Jersey, New England, eastern have resulted in temporary grasslands (Runkle Ontario, and the Canadian Maritimes) were 1990). the result of natural disturbances such as fi re, The extent of grassland habitat in northeast- wind, disease, beaver (Castor canadensis) activ- ern North America has changed drastically over ity, fl ooding, and insect damage. These habitats the past 400 years, in conjunction with changing are now more commonly a product of human land-use practices. Population declines in grass- disturbances, including farming and manage- land birds in the 20th century are the result of ment of conservation areas to provide habitat habitat loss resulting from forest succession, for rare species (Askins 1999, 2000). human development (Vickery and Dunwiddie Fire has been an important disturbance 1997), and fi re suppression (Patt erson and mechanism in northeastern North America, Sassaman 1988, Vickery et al. 2005). In addition, especially in coastal areas that have sandy soils more intensive agricultural practices, such as and support fi re-adapted trees and vegeta- converting hay fi elds to alfalfa (Medicago sativa), tion such as pitch pine (Pinus rigida) and litt le have substantially reduced grassland bird habi- bluestem (Schizachyrium scoparium). However, tat. Finally, earlier and more frequent mowing the historical frequency, intensity, and source of remaining hay fi elds has made them less suit- of these ignitions are less clear (Patt erson and able for grassland birds because of destruction Sassaman 1988, Parshall and Foster 2002). The of nests (Bollinger and Gavin 1989, Jones and presence of large sandplain grasslands along Vickery 1997). the coastal lowlands from New York to Maine Grassland bird assemblage.—Fift een species of before European sett lement provides strong obligate grassland birds (sensu Vickery et al. evidence that fi res were frequent enough to 1999b) breed in northeastern North America. maintain open habitats suitable for grassland Horned Larks (Eremophila alpestris) and birds (Vickery and Dunwiddie 1997, Askins Vesper Sparrows (Pooecetes gramineus) prefer 1999). The Hempstead Plains, a 24,000-ha sparse vegetation with large amounts of bare grassland on Long Island, New York, that ground. Grasshopper Sparrows (Ammodramus once supported a full complement of grass- savannarum) typically select somewhat denser land birds, including the extinct Heath Hen grassland vegetation, oft en with native bunch- (Tympanuchus cupido cupido; Askins 1997), was grasses, such as litt le bluestem or poverty grass one of the most striking examples of these (Danthonia spicata; Bollinger 1995). Savannah large grasslands. Sparrows, Bobolinks, and Eastern Meadowlarks Most of the pre-Columbian Northeast was breed in a wider range of grasslands, includ- heavily forested (Norment 2002): large open- ing dense rhizomatous hay fi elds with exotic ings that depended on fi re were widely scat- grasses such as timothy (Phleum pratense) (Wiens tered, and many may have been created by 1969, Vickery et al. 1999a, Shriver et al. 2005). periodic burning by Native Americans. Other Upland Sandpipers (Bartramia longicauda) toler- forms of disturbance provided habitat for grass- ate a range of grassland conditions but appear land birds, however. Until their widespread to select sites with substantial heterogeneity extirpation in the Northeast in the 18th cen- (Vickery et al. 1994). Henslow’s Sparrows (A. tury, beavers created large “beaver meadows,” henslowii) and Short-eared Owls (Asio fl ammeus) especially in fl at fl oodplains. Before most rivers generally prefer thicker, oft en moist grasslands were dammed, frequent seasonal fl ooding also (Holt and Leasure 1993, Herkert et al. 2002). resulted in wet meadows in fl oodplains. These Between 1997 and 2000, a regional survey habitats would have been suitable for spe- of breeding grassland birds in New England cies of grassland birds, such as Bobolinks and and New York estimated the occurrence and Savannah Sparrows (Passerculus sandwichensis), relative abundance of seven obligate grassland that can nest in relatively small areas of grass- bird species at 1,140 sites (Shriver et al. 2005). land (Askins 1999). Presumably windthrows Sites included hay fi elds, fallow fi elds, pastures, CONSERVATION OF GRASSLAND BIRDS 5 airports, and military bases. Of the seven species 1978). For example, in Pennsylvania, there are surveyed, Savannah Sparrows and Bobolinks ~35,000 ha of reclaimed surface mines that sup- were most common, occurring on 72% and 69% of port high densities of grassland birds, includ- all sites, respectively. Eastern Meadowlarks were ing Grasshopper Sparrows and Henslow’s detected on 37% of the sites. Upland Sandpipers, Sparrows (Matt ice et al. 2005). Reclaimed Vesper Sparrows, Grasshopper Sparrows, and grasslands are also found in West Virginia, Henslow’s Sparrows were generally uncommon Virginia, Ohio, and Indiana (Bajema et al. 2001, and occurred on <20% of the sites. DeVault et al. 2002). Nest success of grassland Current habitat for grassland birds.—Privately birds in a relatively small reclaimed surface owned agricultural land clearly represents the mine in West Virginia was apparently too low largest proportion of graminoid-dominated to sustain their populations (Wray et al. 1982), open land in northeastern North America. In but preliminary results of research in larger 1997, there were 1,760,000 ha of open farmland reclaimed surface-mine grasslands in Indiana in New England, of which ~720,000 ha were indicate that grassland birds were reproduc- hay fi elds, pastures, and idle cropland (data ing successfully (DeVault et al. 2002). Also, from National Agricultural Statistics Service; Henslow’s Sparrows had similar nest-success see Acknowledgments). These habitats are rates on reclaimed mine sites and nonmined most likely to provide suitable nesting habi- sites in Kentucky (Monroe and Ritchison 2005). tat for grassland birds. Commercial lowbush Additional studies are needed in the Northeast blueberry (Vaccinium angustifolium) barrens, to determine whether reclaimed surface mines located primarily on sandy glacio-marine del- can provide good breeding habitat for grass- tas in northeastern North America, constitute land birds. a unique type of agricultural landscape that is Managing habitat for grassland birds.— very important to grassland birds, especially Presently, grassland habitat in northeastern Upland Sandpipers and Vesper Sparrows (Weik North America is created and maintained 1998, Shriver et al. 2005). The vegetation of the primarily as a result of three types of habi- barrens comprises native grasses, shrubs, and tat management: mowing, livestock grazing, trees that are adapted to frequent fi res. Fire has and prescribed burning. In New England, been a regular component on some of these bar- hay fi elds and pastures compose the largest rens for >1,700 years, and palynological evidence proportion of open land, and traditionally suggests that the habitat in these xeric areas was these fi elds have been mowed or grazed. The some form of grassland pine–shrub barren ~355,000 ha of hay fi elds in New England are (Winne 1997). Presently managed for lowbush cut one or more times annually. Although hay blueberry production by regular mowing and fi elds make up >50% of the grassland habitat burning, these barrens occupy >50,000 ha, with in the Northeast, early and frequent mowing 26,000 ha in Maine (D. Yarborough pers. comm.) schedules are likely to make many of these hay and 26,700 ha in the Canadian Maritimes fi elds substantial population sinks (Bollinger (K. McAloney pers. comm.). and Gavin 1992). Federal, state, and municipal grasslands Livestock grazing is an important form of account for a small fraction of the total grassland habitat management that aff ects grassland birds. habitat in northeastern North America. Despite In New York, Smith (1997) found that moderate the small proportion of public grassland habi- grazing with stocking rates of 0.12–0.24 head of tat, some of these sites support large numbers of catt le per hectare provided adequate habitat for regionally threatened grassland birds. Because Henslow’s and Grasshopper sparrows in the of their size, many airports in the Northeast are Finger Lakes National Forest. important for grassland birds, especially species Modifi cations in habitat management such as Upland Sandpipers and Grasshopper practices at military and municipal airports Sparrows that require large areas of continuous have clearly benefi ted grassland birds. These grassland (Melvin 1994, Jones and Vickery 1997; practices include deferred mowing schedules Fig. 1). and reduced vehicular traffi c in grassland Although of recent origin, reclaimed surface areas. For example, at Westover Air Reserve mines in eastern North America provide exten- Base, Chicopee, Massachusett s, populations of sive grassland habitat (Whitmore and Hall Upland Sandpipers and Grasshopper Sparrows 6 ORNITHOLOGICAL MONOGRAPHS NO. 64

Fig. 1. Frequency of occurrence of six species of grassland birds in grasslands of different sizes in coastal Maine (Vickery et al. 1994; reprinted with permission from Blackwell Publishing). have increased by >200% as a result of these on blueberry lands is not accurately recorded, management changes (Melvin 1994, Jones and but these ignitions are much larger than the Vickery 1997). prescribed burns on conservation lands, prob- Prescribed fi re is used primarily for two ably on the order of 20–100+ ha (P. Vickery reasons: habitat management of rare plant pers. obs.). (Vickery 2002a, b) and animal assemblages and The scale of “ecological” prescribed burns maintenance of commercial lowbush blueberry in northeastern North America for grassland fi elds (Fig. 2). Prescribed fi re is used on com- management has been small; since 1990, <400 ha mercial blueberry barrens to prune blueberry have been burned annually in New England, plants, reduce litt er, and reduce pest insect den- and burned areas were usually <15 ha (T. sities; in Maine, ~3,000 ha are burned annually Maloney unpubl. data). Despite the small size (D. Yarborough pers. comm.). The size of fi res of these burns, they can have important benefi ts CONSERVATION OF GRASSLAND BIRDS 7

Fig. 2. Northern Blazing Star (Liatris borealis novae-angliae), one of the endemic perennials growing on eastern sandplain grasslands, at the Kennebunk Plains, York County, Maine. This grassland is an important breeding area for Upland Sandpipers, Grasshopper Sparrows, and numerous other grassland birds. (Photograph by P. D. Vickery.) for grassland birds, at least locally. In an eight- Southeastern Pine Savannas year study on a 210-ha sandplain grassland in Kennebunk, Maine, densities of Savannah We include southeastern pine savannas to Sparrows, Grasshopper Sparrows, Bobolinks, emphasize that a wide variety of diff erent habi- and Eastern Meadowlarks declined for one tat types support grassland birds, and because year immediately following fi re but then were pine savannas were historically the dominant quite high for the subsequent fi ve to seven vegetation over vast expanses of the Southeast years (Vickery et al. 1999a). By contrast, Horned and are important native habitats for several Larks and Vesper Sparrows preferred recently declining grassland birds in eastern North burned sites. Abundances of these two species America. and Upland Sandpipers generally declined with History of grasslands.—Pine lands occurred time since fi re. historically over 25 million hectares of the Although appropriate management of air- southeastern coastal plain (Fig. 3). Longleaf fi elds and protected natural areas is impor- pine (Pinus palustris) savannas covered a vast tant for the future of grassland birds in the expanse from extreme southeastern Virginia, Northeast, farmland remains the greatest south through Florida, and west through potential source of habitat for many of these southern Mississippi, parts of Louisiana, and species (Shriver et al. 2005, Vickery et al. 2005). east Texas, and other pine savanna communi- Providing farmers with economic incentives ties occurred in smaller patches farther inland to manage their land for conservation as well and upland. The distribution of wiregrass as agricultural production could help sustain (Aristida stricta) was more limited, extend- grassland bird populations while preserving ing north into North Carolina and west into historically important rural landscapes. southern Mississippi (Stout and Marion 1993). 8 ORNITHOLOGICAL MONOGRAPHS NO. 64

Pollen studies suggest that the southeastern 1995) or 5–10 years (Ware et al. 1993), and even coastal plain was dominated by pines for the less frequently (6–15 years) on poorer-quality past 5,000 years, and for 3,500 years before that sites (Stanturf et al. 2002). Frequent ground fi res by oak forest, scrub, and savanna with scat- apparently were the normal patt ern in longleaf tered bluestem prairie (Watt s 1971). systems (Williamson and Black 1981, Platt et al. Southeastern pine savannas are naturally 1988); they were frequent and pervasive enough pyrogenic systems. Longleaf pine fl atwoods to qualify as an ecological driver under our and sandhills probably burned at one- to defi nition. Occupying wett er depressions, slash three-year intervals (Stout and Marion 1993), pine and pond pine burn less frequently than whereas in areas dominated by other species longleaf stands, and pond pine is more subject of pine, including mixed pine–hardwood areas to occasional crown fi res (Abrahamson and farther inland, and in semiprotected areas the Hartnett 1990, Stout and Marion 1993). The for- fi re intervals were longer (Stanturf et al. 2002). mer system can be described as an understory For instance, shortleaf pine (P. echinata) in the fi re regime and the latt er as a mixed fi re regime, Ouachita Mountains of Arkansas generally which removes 20–80% of the canopy (Stanturf burned at intervals of 4–6 years (Wilson et al. et al. 2002).

Fig. 3. Historical distribution of pine savannas and transition woodlands in the southeastern United States (Engstrom et al. 2005). These habitats support breeding populations of birds such as Bachman’s Sparrows and Loggerhead Shrikes, and wintering populations of Loggerhead Shrikes and Henslow’s Sparrows. (Reprinted from Studies in Avian Biology by permission of The Cooper Ornithological Society.) CONSERVATION OF GRASSLAND BIRDS 9

Lightning strikes, which occur most fre- is limited to the southeastern United States. quently in late spring or early summer, were American Kestrel, Red-headed Woodpecker, the primary source of fi res before human sett le- Loggerhead Shrike, and Eastern Bluebird all ment (Stout and Marion 1993). Native American require open areas for foraging and trees for burning occurred primarily in fall and winter nesting, so their habitat requirements are met (Ware et al. 1993), as does much recent pre- by savannas (Yosef 1996, Cade and Woods 1997, scribed burning (Platt et al. 1988). Near the Gowaty and Plissner 1998, Smith et al. 2000, coast, where topographic fi rebreaks were lack- Smallwood and Bird 2002). Although com- ing, a single ignition likely burned large areas, monly thought of as shrub nesters, Loggerhead on the order of 1,000 km2. Farther inland and Shrikes in pine savannas regularly nest high on on moister soil, compartments were probably limbs of mature longleaf pines (R. T. Engstrom smaller and burned less frequently (Ware et al. pers. comm.). Some breeding species, such 1993). In the Ouachita Mountains of Oklahoma, as Brown-headed Nuthatch (Sitt a pusilla) and presett lement fi res covered 300–800 ha (Masters Red-cockaded Woodpecker (Picoides borealis), et al. 1995). that are not known to use the grassland layer Slight variations in topography and soil char- nevertheless seem to respond to changes in acteristics create variations in susceptibility to understory vegetation (Walters 1991, Wilson fi re, resulting in extensive “interdigitation” of and Watt s 1999). habitat types (Stout and Marion 1993). In con- Although not emphasized here, pine savan- trast to prairie habitats, where time since last nas provide important wintering habitat for burn infl uences which suite of grassland bird some additional species, notably Henslow’s species are seen on particular patches, grass- Sparrow (Hamel 1992, Plentovich et al. 1999, land bird species of southeastern pine savannas Tucker and Robinson 2003), which prefers sites all depend on frequent burns (i.e., every two to with greater herbaceous vegetation and less three years). Without fi re, pine savannas rapidly leaf litt er (Carrie et al. 2002). Abundance of succeed into hardwood forests, eliminating hab- Henslow’s Sparrow in winter is much greater itat for grassland birds (Stout and Marion 1993, on sites burned in the previous growing season, Ware et al. 1993). Dry conditions combined with apparently because this stimulates produc- annual fi re can create and maintain treeless tion of grass seeds used as food (Bechtoldt grasslands (Ware et al. 1993), and these may and Stouff er 2005). Suppression of hardwood be important for species, such as Grasshopper midstory is also important to wintering birds Sparrow, that do not tolerate a pine overstory. (Provencher et al. 2002a). Field Sparrow (Spizella The dry prairies of Florida are similar to pine pusilla) and Vesper Sparrow are found in pine fl atwoods but lack the pine overstory. The savannas in winter, but primarily use early suc- absence of trees may be a result of diff erences cessional stages instead of sites with a mature in hydrology, but this is not clear. At least some pine overstory (Hamel 1992). areas are maintained without trees because of In the absence of fi res, rapid encroach- unusually frequent burning, and clear-cutt ing ment of woody vegetation in these habitats and livestock grazing have also been shown leads to population declines of grassland to create treeless grasslands (Abrahamson and birds (Engstrom et al. 2005). In north Florida, Hartnett 1990). Bachman’s Sparrows, Blue Grosbeaks (Passerina Grassland bird assemblage.—Although sev- caerulea), Eastern Kingbirds (Tyrannus tyran- eral bird species use the grassy component of nus), and Loggerhead Shrikes disappeared southeastern pine savannas, these savannas quickly (within fi ve years) following fi re are probably the dominant breeding habitat in exclusion (Engstrom et al. 1984, Brennan et the Southeast for only six species of grassland al. 1998). In shortleaf pine–bluestem savanna and savanna specialists: American Kestrel (Falco in Arkansas, densities of ground–shrub forag- sparverius), Northern Bobwhite (Colinus virgin- ers and ground-nesting birds were higher in ianus), Red-headed Woodpecker (Melanerpes stands that were treated by thinning, burning, erythrocephalus), Loggerhead Shrike (Lanius or both than in unmanaged controls (Wilson ludovicianus), Eastern Bluebird (Sialia sialis), et al. 1995). In Georgia, 29 of 46 breeding bird and Bachman’s Sparrow (Aimophila aestivalis). species showed signifi cantly diff erent habitat Of these species, only Bachman’s Sparrow preferences for recently burned (1–3 years) 10 ORNITHOLOGICAL MONOGRAPHS NO. 64 and unburned (>20 years) sites, 22 of these densities that do not create savanna conditions, species occurring more frequently in recently but this is changing. burned sites (White et al. 1999). Species that Less than 2–3% of the original upland vegeta- were signifi cantly more common in burned tion of the southeastern pine savannas remains sites included Northern Flicker (Colaptes intact (Noss 1989, Ware et al. 1993, Wear and auratus), Prairie Warbler (Dendroica discolor), Greis 2002), and even on these sites management Bachman’s Sparrow, Chipping Sparrow (S. pas- may be inappropriate (Ware et al. 1993). Only serina), Field Sparrow, Brown-headed Cowbird 11% (21 million acres) of southern forestland is (Molothrus ater), and American Goldfi nch in public ownership. Most is managed by the (Carduelis tristis). So few nests were found on U.S. Forest Service, but one-third of this area (7 unburned sites that it was impossible to com- million acres) is administered by other agencies, pare productivity. including state, county, municipal, and tribal Current habitat for grassland birds.—Loss of governments (Fig. 4). The remaining 89% of the native habitat and fi re suppression are major land is controlled by >5 million private landown- causes of population decline for grassland birds ers, 18% of whom own industrial forests (Wear in the southeastern pine savanna region (Jackson and Greis 2002). Because most old-growth long- 1988, Dunning and Watt s 1990, Engstrom et al. leaf pine stands are privately owned, eff orts to 1996, Tucker et al. 1998). Urbanization has been acquire land and to encourage private landown- the primary cause of the loss of forestland in the ers to manage for endangered species have been Southeast for the past two decades (Wear and important for conservation (Stout and Marion Greis 2002). Native pine stands are also being 1993, Ware et al. 1993). However, the largest rapidly replaced by pine plantations. Planted remaining stands of longleaf pine occur on pub- pine stands now occupy 48% of the pine lands lic land, with a few exceptions (including the in the region, compared to 1% in 1952 (Wear and Moody tract in south Georgia and Green Swamp Greis 2002). Most of these have been planted at in North Carolina; Wear and Greis 2002).

Fig. 4. Longleaf pine–wiregrass savanna, Eglin Air Force Base, Okaloosa County, Florida. This plot was pho- tographed in April after a summer burn the previous June. (Photograph by Lori Blanc.) CONSERVATION OF GRASSLAND BIRDS 11

Because human activity has removed much plantations are unlikely to provide good habitat of the naturally pyrogenic vegetation and for grassland birds except in the fi rst few years. introduced numerous fi rebreaks such as roads, For example, natural longleaf pine forests had there is litt le opportunity for lightning-ignited two to four times higher densities of breeding fi res to burn with the frequency or to the extent birds in the ground-foraging and ground- they did historically. Ware et al. (1993:483) aptly nesting guilds compared with almost all age- described the situation as “fi ner and fi ner parti- classes of slash pine plantations (Repenning tioning of the landscape into fi re-protected com- and Labisky 1985). In South Carolina, very partments,” putt ing the savanna ecosystem “in young (2–6 years) longleaf pine plantations immediate danger of extinction.” Consequently, supported more bird species than mid-aged implementing artifi cial disturbances is essential (>32 years) longleaf stands that regenerated for maintaining the native bird fauna of the from old fi elds, but no comparison was made southeastern pine savannas. with old-growth stands. Bachman’s Sparrows, Managing habitat for grassland birds.—Methods Loggerhead Shrikes, and Eastern Kingbirds that prevent or remove encroachment of a hard- were detected on these sites (Krementz and wood understory are required to maintain suit- Christie 1999). able habitat for grassland-dependent species in Changes since the turn of the 21st century pine savannas. Both thinning and prescribed in pine plantation management, however, may burning are known to maintain habitat for create much more suitable habitat for grassland grassland species in Arkansas (Wilson et al. birds. Increasing prices for sawtimber as com- 1995). An experimental comparison of burning, pared with pulpwood have made large trees mechanical, and herbicide control of hardwood much more valuable. Consequently, standard midstory in Florida longleaf pine demonstrated planting densities for loblolly pine (Pinus taeda) positive responses of most early-successional and slash pine (P. elliott ii) plantations are now 500 species to all these techniques (Provencher et trees acre–1, down from 900 trees acre–1 a decade al. 2002b, 2003). However, burning is usually ago, allowing much more light to penetrate the signifi cantly more cost-eff ective than other understory (T. R. Fox pers. comm., Virginia Tech techniques (Provencher et al. 2002a). In gen- Department of Forestry). Following one or more eral, some disturbance is required every two to thinnings at about age 12–16, to 200–300 trees three years, with a range of one to fi ve years. acre–1, or, in the case of intensively managed Pine-grassland restoration for Red-cockaded plantations, only 80–100 trees acre–1 (Visser and Woodpeckers increased avian species richness Stampfer 2003), combined with mechanical and and abundance and favored grassland birds and chemical treatment to remove hardwood com- bird species of very high management concern petition, these stands can support the grassy (Conner et al. 2002, Tucker et al. 2003, Wood understory required by grassland birds. Given et al. 2004). Grazing and browsing by catt le or not only increased thinnings, but also the reduc- deer did not have major eff ects on understory tion of rotation lengths for southern pines under plants in longleaf pine–bluestem savannas in intensive management to only 18–25 years (Fox Alabama, but clearcutt ing did (Brockway and et al. 2004), many of these stands probably will Lewis 2003). In North Carolina, fi re-suppressed provide suitable habitat for longer periods and stands had substantially reduced populations of at increasingly frequent intervals. Bachman’s Sparrows, Red-headed Woodpecker, Although all the species described here Prairie Warbler, Brown-headed Nuthatch, and respond positively to burning, Eastern other pine savanna species, compared with sites Bluebirds, American Kestrels, and Red-headed managed with prescribed fi re (Allen et al. 2006). Woodpeckers risk losing cavity trees to fi re. Besides creating desired habitat conditions, The tradeoff between the creation of new snags recent fi re can reduce use of a stand by rac- through burning and the loss of existing cavity coons, potentially resulting in increased nesting trees to fi re is a challenge faced by land man- success in areas with reduced predator activity agers. Expertise of fi re crews experienced at (Jones et al. 2004). burning near active Red-cockaded Woodpecker Unless there is active management to main- cavities could be useful in planning prescribed tain desired understory conditions (including burns to improve habitat for other cavity- frequent burning and intensive thinning), pine nesting species. Once a frequent fi re regime is 12 ORNITHOLOGICAL MONOGRAPHS NO. 64 established and fuel loads are reduced, the risk Sparrows may have trouble colonizing isolated of burning cavity trees during a prescribed fi re patches, so att ention should be paid to distribu- declines dramatically. tion of suitable habitat across the landscape Bachman’s Sparrow is the species closest to (Pulliam et al. 1992, Dunning et al. 1995). being a pine-savanna endemic. It drops out of Eff ective management for grassland birds pine forests within four to fi ve years aft er burn- in southeastern pine savannas will require a ing (Engstrom et al. 1984, Dunning 1993, Tucker diversity of approaches. The paucity of work et al. 2004) but can nest in recent clearcuts one on demography of grassland birds in diff erent to seven years aft er replanting. Current prac- habitats prevents clear evaluation of alterna- tices including fi re suppression and intensive tive practices. Protection of existing old-growth forest management usually do not allow suit- areas should be a priority, because native able understory conditions for this species to understories are diffi cult to restore and old- develop. However, intensively managed mid- growth pine savannas may provide benefi ts aged (17–28 years old) slash pine plantations as yet unidentifi ed. Management to favor a supported Bachman’s Sparrow populations if grassy understory is obviously essential, and burned regularly (within two to four years; this may be accomplished eff ectively through Tucker et al. 1998), though this practice is rela- burning, mowing, and mechanically or chemi- tively uncommon (Fox et al. 2004). Bachman’s cally removing hardwood or dense pine canopy. Sparrow abundance was positively related to When it is possible to mimic natural fi re regimes relative volume of grass but did not respond by burning during the growing season, this is to season of burn (Tucker et al. 1998, Tucker et desirable, especially given that growing-season al. 2004). Sand pine (P. clausa) plantations >20 burns are known to increase seed production years old supported fewer birds than several of native grasses; but when growing-season native habitats (Tucker et al. 2003). Dunning burns are not possible, it is bett er to have winter (1993) gives a good review of the response of burns than to go long periods without burning. this species to forest management activities, Recently implemented practices in pine planta- mentioning that heavy thinning in 45- to 60- tions may recreate the savanna-like conditions year-old pine plantations also provided suit- of native habitats. Although harvest rotations able habitat. are too short to support cavity nesters such Bachman’s Sparrow was one of the few bird as Red-cockaded or Red-headed woodpeck- species to respond positively to restoration of ers, there may be an increase in populations native groundcover in old-fi eld longleaf-pine of grassland birds in these habitats if the cur- stands (Rutledge and Conner 2002). Wintering rent focus on sawtimber production continues. Bachman’s Sparrows occurred with greater rela- Although grassland birds native to northeastern tive abundance at sites with native groundcover North America may have evolved to disperse (Cox and Jones 2004). Estimates of survival among ephemeral patches of early-successional rates did not diff er between young longleaf habitat, the dominance of grassy vegetation in pine plantations and mid-aged longleaf pine the Southeast for several millennia suggests forests growing on old fi elds (Krementz and that southeastern grassland birds may lack this Christie 1999), but no data were available from ability. Managing for large contiguous patches old-growth, fi re-maintained stands. Bachman’s may, therefore, be more critical in the Southeast. Sparrow productivity in Florida dry prairie was Priorities for research include studying demog- not suffi cient to maintain populations (Perkins raphy and dispersal of birds in old-growth et al. 2003) and probably required infl ux from pine savannas and comparing these with other pine savannas. In longleaf habitat, breeding habitats. Responses of grassland birds to burn productivity decreased with number of years season, invasion of exotic plants, and brood since burn but was not related to season of parasitism are also important research topics. burn (Tucker et al. 2006). Home-range size on the Savannah River Site in South Carolina Tallgrass Prairie was signifi cantly larger (which oft en indicates lower habitat quality) in mature pine stands History of grasslands.—The tallgrass prai- than in two-year-old and four-year-old pine rie region of North America extended from stands (Stober and Krementz 2006). Bachman’s southern Manitoba to southern Texas and east CONSERVATION OF GRASSLAND BIRDS 13 to Indiana, with a historical area of 60 million unclear (Steinauer and Collins 1996). The great- hectares (Samson and Knopf 1994). Major eco- est numbers of bison historically occurred in the logical drivers in the tallgrass prairie region mixed-grass prairie region (McDonald 1981), were fi re, grazing, and drought. Fire played a and grazing frequency and intensity were major role in the formation and maintenance of probably greatest in the western portions of tallgrass prairie (Axelrod 1985, Steinauer and the tallgrass prairies close to the mixed grass Collins 1996; Fig. 5). Estimates of historical fi re region. One possible scenario for bison grazing frequency in tallgrass prairie range from two in tallgrass prairie is many small herds in the to fi ve years, but return intervals probably var- dormant and early growing season, the major- ied widely (Bragg 1982, Steinauer and Collins ity migrating to mixed and short-grass areas as 1996). Naturally ignited prairie fi res (primar- the growing season progressed (Steinauer and ily caused by lightning) occurred from March Collins 1996). The frequency, timing, and inten- through December but were most common in sity of grazing by other herbivores in tallgrass mid- to late summer (Bragg 1982, McClain and prairie also are poorly known. Elzinga 1994). Up to half of all fi res in the tall- Droughts occur periodically in tallgrass grass prairie region, however, may have been prairie (Weaver 1954), though the frequency of set by Native Americans (Moore 1972, Higgins such events is lower than in either mixed- or 1986). shortgrass prairies (Wiens 1974). Wiens (1974) Grazers and browsers that historically estimated that unusually wet or dry years inhabited tallgrass prairie included bison (deviation from long-term average by ≥25%) (Bison bison), elk (Cervus elaphus), white-tailed occur in tallgrass prairie about once every deer (Odocoileus virginianus), mule deer (O. four years, and that extremely wet or dry years hemionus), and many small vertebrates and (deviation from long-term average by ≥50%) invertebrates. The extent to which herbivores, occur roughly once every 40 years. Drought especially bison, grazed tallgrass prairie is aff ects tallgrass prairie plant production and

Fig. 5. Spring prescribed fire conducted in a native prairie remnant in northern Illinois (Grundy County). Fire is a major ecological driver in the tallgrass-prairie region of North America. Naturally occurring fires are now rare in the tallgrass region, and most prairie fires are set by range managers and conservationists seeking to maintain prairie habitats. (Photograph by Bill Glass.) 14 ORNITHOLOGICAL MONOGRAPHS NO. 64 diversity (Steinauer and Collins 1996), and Knopf 1994). Losses have been highest in the this in turn has the potential to infl uence eastern portion of the range, with Kansas (1.2 bird populations. Zimmerman (1992) found million hectares remaining), Texas (720,000 ha), that March soil moisture was signifi cantly and South Dakota (449,000 ha) currently pos- correlated with total bird abundance in both sessing the greatest remaining acreage of pre- burned and unburned Kansas tallgrass prai- sett lement prairie. Most of this is in private rie, but that the abundance of a subset of core ownership, though several large conservation grassland-dependent species was related to areas have been established, including Konza March soil moisture in burned tallgrass prai- Prairie Long Term Ecological Research Site in rie but not in unburned prairie. In Illinois, Kansas (3,487 ha), The Nature Conservancy’s Henslow’s Sparrow populations were found Tallgrass Preserve in Oklahoma (15,384 ha), and to be correlated with spring (January–April) the Tallgrass Prairie National Reserve in Kansas precipitation, increasing in years when spring (4,410 ha). precipitation was greater than in the preceding A variety of nonnative grasslands, such as year and declining in years when precipitation pasture and hay fi elds, now constitute a major- declined (Herkert and Glass 1999). ity of the grassland habitat in the tallgrass Grassland bird community.—Currently, 16 region (Herkert et al. 1996), especially in the species of obligate grassland birds (Vickery et eastern portion of the area. These grasslands al. 1999b) breed in the tallgrass prairie region are almost exclusively privately held, and of North America. Characteristic species their acreage has declined sharply during the include Dickcissel (Spiza americana), Eastern past 40 years (Herkert et al. 1996). Population Meadowlark, Bobolink, Henslow’s Sparrow, declines of several species of grassland birds Grasshopper Sparrow, Sedge Wren (Cistothorus in the region, such as Grasshopper Sparrow, platensis), Upland Sandpiper, and Greater Prairie- Eastern Meadowlark, Dickcissel, Bobolink, Chicken (Tympanuchus cupido) (Zimmerman Western Meadowlark (Sturnella neglecta), and 1993, 1996; Winter 1998; J. R. Herkert unpubl. Savannah Sparrow, are strongly correlated data). Among these species, Henslow’s Sparrows with reductions in regional pasture and hay and Sedge Wrens prefer tall, dense vegetation, acreage (Herkert et al. 1996). New sources of usually with a well-developed litt er layer (Wiens habitat for grassland birds have been created 1969; Herkert et al. 2001, 2002); Dickcissels and during this period, however. Recent investiga- Bobolinks prefer moderate to tall vegetation, tions of breeding birds in former strip-mines also with well-developed litt er (Wiens 1969, have shown that some of these areas can sup- Skinner et al. 1984, Sample 1989, Bollinger 1995); port relatively large populations of several Greater Prairie-Chickens, Eastern Meadowlarks, characteristic tallgrass-prairie birds, including and Grasshopper Sparrows prefer vegetation of Grasshopper Sparrows, Eastern Meadowlarks, intermediate height (Wiens 1969, Vickery 1996, and Henslow’s Sparrows (Bajema et al. 2001, McCarthy et al. 1997); and Upland Sandpipers Ingold 2002, Scott et al. 2002). Grasslands estab- prefer short to moderate vegetation (Skinner lished by the Conservation Reserve Program et al. 1984, Sample 1989). Most tallgrass-prairie (CRP; see below) in the tallgrass region also grassland birds also prefer areas with low levels support good populations of prairie birds, of woody vegetation. Other species of birds com- including Bobolinks, Dickcissels, Grasshopper monly found in tallgrass prairies include Red- Sparrows, and Henslow’s Sparrows (Best et winged Blackbird (Agelaius phoeniceus), Common al. 1997, Harroff 2001). Conservation Reserve Yellowthroat (Geothlypis trichas), Mourning Program grasslands have been planted to Dove (Zenaida macroura), Eastern Kingbird, both native warm-season grasses and non- American Goldfi nch, Northern Bobwhite, and native cool-season grasses. Species richness, Field Sparrow. Most of the secondary species are overall abundance, and nest success appear associated with low to moderate levels of woody to be similar in warm-season and cool-season vegetation. CRP grasslands (e.g., Delisle and Savidge Current habitat for grassland birds.—Native 1997, McCoy et al. 2001) and, in Iowa, species tallgrass prairie has been greatly diminished richness and densities of most common bird range-wide, with only ~4% of presett lement species were found to be similar in restored tallgrass prairie now remaining (Samson and CRP grasslands and nearby tallgrass-prairie CONSERVATION OF GRASSLAND BIRDS 15 remnants, except for Grasshopper and edge habitat on nest-parasitism rates in grass- Savannah sparrows, which were more dense land birds may be more apparent in areas of in restored grasslands (Fletcher and Koford low cowbird density than in areas with high 2002). The creation of a large acreage of grass- cowbird densities (Jensen and Cully 2005a). lands by the CRP also seems to have benefi ted Woody encroachment is also having major populations of some grassland bird species. For eff ects on grassland birds in the tallgrass-prairie example, regional populations of Grasshopper region. Woody species are increasing in cover and Henslow’s sparrows increased following and abundance in many areas of the tallgrass the creation of additional breeding grassland region (Briggs et al. 2002, Hoch et al. 2002, habitat by the CRP (Herkert 1997, 1998, 2007), Heisler et al. 2003), and woody-plant expansion which suggests that the availability of breeding may be one of the greatest contemporary threats habitat is infl uencing recent population trends to mesic grasslands of the central United States for some tallgrass-prairie bird species and that (Briggs et al. 2005). This expansion is occurring large-scale grassland-restoration (such as that because of altered fi re and grazing regimes that accomplished by the CRP) can help reverse provide the opportunity for recruitment of new recent population declines. individuals and of additional shrub and tree As grassland area declines, several species of species (Briggs et al. 2005). Once established, grassland birds have been shown to be nega- woody cover tends to increase regardless of tively aff ected by the subsequent reductions fi re frequency, and infrequent fi res accelerate in patch size, in terms of both reduced abun- the spread of some species (Briggs et al. 2005). dance (Herkert 1994b, Helzer and Jelinski 1999, This process is resulting in a new dynamic state Winter and Faaborg 1999, Horn et al. 2002) and of shrub–grass coexistence (Briggs et al. 2005), reduced nesting success (Johnson and Temple which has important implications for breed- 1990, Winter and Faaborg 1999, Herkert et al. ing birds. Landscape-level increases in woody 2003) within small patches of grassland habitat. vegetation are linked to regional population However, the infl uence of patch size on grass- declines of grassland birds (Coppedge et al. land birds may vary among years, regions, and 2001a, b), whereas local increases in woody species (Winter et al. 2006). Another conse- vegetation have negative eff ects on patch-level quence of reduced patch sizes is an increase in abundance and nesting success for many grass- edge habitat. Many grassland birds avoid habi- land species (Johnson and Temple 1990, Hughes tat edges (Lima and Valone 1991, Delisle and et al. 1999, Winter et al. 2000, Patt en et al. 2006). Savidge 1996, Helzer 1996, Fletcher and Koford Without drastic measures, such as mechanical 2003, Bollinger and Gavin 2004). However, removal of shrubs, it is unlikely that manage- woody edges appear to exert the strongest ment of fi re and grazing regimes alone will be infl uence on grassland bird populations, suffi cient to restore historical grass dominance reducing bird abundance and nest density and in these ecosystems (Briggs et al. 2005). increasing rates of nest predation (Johnson and Managing habitat for grassland birds.—Fire, Temple 1986, 1990; Winter et al. 2000; Bollinger grazing, and mowing are the three most com- and Gavin 2004). Edge eff ects may be more mon management techniques in the tallgrass pronounced and extend farther into grasslands region. In the western portion of the tallgrass with multiple edges (Fletcher 2005), so the nega- region, Upland Sandpipers, Eastern Kingbirds, tive eff ects of edges may be diffi cult to avoid in and Red-winged Blackbirds are most abun- highly fragmented, edge-dominated landscapes dant in burned prairie, whereas Dickcissels, (Renfrew et al. 2005). Grasshopper Sparrows, Eastern Meadowlarks, Woody habitat edges in tallgrass prairie also Henslow’s Sparrows, and Brown-headed have been shown to increase rates of nest para- Cowbirds are most abundant in unburned sitism by Brown-headed Cowbirds (Johnson grasslands (Zimmerman 1992, Powell 2006). and Temple 1990, Jensen and Finck 2004, Patt en Several species of facultative grassland birds et al. 2006). However, regional cowbird abun- (Vickery et al. 1999b) are also more common dance also infl uences cowbird parasitism rates in unburned prairie because of their depen- in prairie birds; parasitism rates are highest in dence on woody vegetation, which tends to regions of high cowbird abundance (Herkert et be more common in unburned prairie (Briggs al. 2003, Jensen and Cully 2005b). The eff ect of et al. 2002). These species include Bell’s Vireo 16 ORNITHOLOGICAL MONOGRAPHS NO. 64

(Vireo bellii), Brown Thrasher (Toxostoma rufum), Sparrows, Greater Prairie-Chickens, and Eastern Blue Grosbeak, and American Goldfi nch Meadowlarks, whereas heavy grazing (<20% (Zimmerman 1992). In the eastern portion combined grass and forb cover at 25 cm) favored of the tallgrass region, Bobolinks tend to be Upland Sandpipers, Western Meadowlarks, and more abundant in recently burned areas, and Horned Larks (Skinner et al. 1984). Henslow’s Common Yellowthroat and Henslow’s Sparrow Sparrows and Sedge Wrens are generally are more abundant in unburned areas (Herkert rare or absent in grazed grasslands. In south- 1994a, Johnson and Temple 1986, J. R. Herkert central Illinois, light, late-season grazing of unpubl. data). Management response of breed- warm-season grasses resulted in higher densi- ing birds to prairie fi res may also be infl uenced ties of Eastern Meadowlarks, Dickcissels, and by other factors, such as prairie size. In Missouri Grasshopper Sparrows compared with undis- tallgrass prairies, Winter (1998) reported that turbed warm-season fi elds (Walk and Warner changes in Henslow’s Sparrow density in 2000). Henslow’s Sparrows, however, were more response to fi re were greater in large prairies numerous in undisturbed fi elds in Illinois (Walk than in small prairies. Because some birds and Warner 2000). respond positively and others negatively to fi re, Studies of the eff ects of grazing on nest suc- a rotational management program is usually cess of birds in the tallgrass region have pro- suggested, whereby small portions of prairies duced varying results. Some studies have found are burned rotationally, with three to fi ve years that grazing reduces nest success (Temple et al. between burns (Zimmerman 1988, Herkert 1999, Shochat et al. 2005, Sutt er and Ritchison 1994c, Winter 1998; Fig. 6). 2005), whereas others have found no diff erence Grazing also has a signifi cant eff ect on many in nest success between grazed and ungrazed grassland bird species; some species prefer areas (Zimmerman 1996, Klute et al. 1997). Sites grazed areas, and others avoid them. In Kansas managed with a combination of grazing and tallgrass prairie, grazing by bison resulted in burning, however, have signifi cantly lower nest increased abundance of Upland Sandpipers success than unburned prairie (Zimmerman and Grasshopper Sparrows and nearly elimi- 1996, Shochat et al. 2005). nated Henslow’s Sparrows (Powell 2006). In A promising new approach to tallgrass-prairie Missouri tallgrass prairie, moderate grazing management involves burning discrete patches (20–40% combined grass and forb cover at 25 cm) of prairie and then allowing free-ranging tended to favor populations of Grasshopper grazers (either bison or catt le) to selectively

Fig. 6. Midsummer picture (May 28) looking down the border of a spring prescribed fire in a tallgrass-prairie remnant in Illinois. The burned portion is on the left side of the photograph and the unburned portion on the right side; the residual vegetation is visible on the unburned portion. Fire removes residual vegetation and litter and is important in controlling woody invasion in tallgrass prairies. (Photograph by J. R. Herkert.) CONSERVATION OF GRASSLAND BIRDS 17 graze areas of burned and unburned prairie the shortgrass prairie extended into North and (Fuhlendorf and Engle 2004). This management South Dakota and Montana along river valleys approach has been shown to generate a more that were heavily grazed by bison. Aft er bison heterogeneous mosaic of grassland types that were extirpated and cool-season grasses were may enhance the diversity of grassland species introduced by ranchers, the tongues of short- by mimicking grazing patt erns before European grass prairie in this northern region were sup- sett lement (Fuhlendorf and Engle 2001). planted by mixed-grass prairie, so we include The abundance of some grassland bird spe- this region in the “northern plains” section cies, especially Bobolinks and Grasshopper (below), along with the mixed-grass prairie of Sparrows, is also high in recently hayed areas western Canada. (Winter 1998, Swengel and Swengel 2001, J. R. Drought was the primary ecological driver Herkert unpubl. data), but studies comparing of this landscape. Unlike the tallgrass prairie the relative merits of haying versus burning (historically known as the true prairie) to the also produced confl icting results. In Missouri, east of the 100th meridian, where fi re was an Swengel and Swengel (2001) found that fi elds important ecological driver, the shortgrass maintained by rotational haying every one to prairie was secondarily maintained by grazing four years had higher densities of Henslow’s (Fig. 7). The primary grazers were black-tailed Sparrows than fi elds maintained with spring prairie-dogs (C. ludvicianus), bison, and elk burning. However, other studies indicate that (wapiti), in that order. Pronghorn (Antilocapra haying can reduce densities of Henslow’s americana), which selectively forage on forbs Sparrows and other grassland species that rather than grasses, were also present (Knopf prefer taller, more dense vegetation (Cully and and Samson 1997). Michaels 2000), and another study in Missouri The historical frequency, intensity, and extent prairies did not detect a diff erence in Henslow’s of grazing on the southern Great Plains are Sparrow density in burned versus mowed poorly understood. Elk occurred primarily on prairies (Winter 1998). The timing of grassland the eastern half of the Great Plains (eastern cutt ing is another concern associated with Nebraska, Kansas, and Oklahoma), where they mowing–haying of grasslands in the tallgrass foraged in small herds. Elk were apparently region. Cutt ing during the nesting season is more frequent in the vicinity of riverbott om likely a bigger issue in agricultural grasslands, areas, where ranker grasses were present, and such as hay fi elds, than in prairie habitats, the eff ects of their grazing were probably not because agricultural grasslands are generally great, given the small size of the herds. Bison, cut earlier and more frequently than prairies on the other hand, grazed on the high plains in the region, but haying in tallgrass prairies is in extensive herds, likely numbering at least in also known to destroy nests (Winter 1998). the tens of millions (Shaw 1995). Many authors refer to the annual movement patt erns of bison Shortgrass Prairie creating a “grazing mosaic,” though specifi c information on a regular patt erning of move- History of grasslands.—The area currently ment is lacking. Because of the presence of large designated “shortgrass prairie” was histori- bison herds along the Missouri, Republican, cally known as the Great Plains, because of Arkansas, Cimarron, and Canadian rivers the barrenness of the landscape. Beginning at (which served as water sources), much of what the 100th meridian and extending to the Rocky is today called “mixed-grass prairie” was short- Mountains, the grasses became short and the grass prairie historically (Hart 2001). Although horizon treeless. The boundary between tall- it is tempting to att ribute the development of grass and shortgrass prairie was a “feathered the mixed-grass prairie to diff erential foraging edge” that ran through eastern Nebraska, by catt le as compared with bison, the reality Kansas, and Oklahoma into central Texas. is that the introduction of grazing practices With the elimination of bison and prairie-dogs, (managing catt le stocking rates and seasonal mixed-grass prairie supplanted shortgrass prai- timing) in which fences are used to control and rie in this boundary zone because taller grass standardize grazing pressure probably had a shaded out buff alo grass (Buchloe dactyloides) larger eff ect on bird habitats in the Great Plains and blue grama (Bouteloua gracilis). In the north, (Samson et al. 2004) than the displacement 18 ORNITHOLOGICAL MONOGRAPHS NO. 64

Fig. 7. The shortgrass prairie, as seen here in Weld County, Colorado, evolved with intensive grazing pressure that results in native grasses with 90% of the biomass below ground to protect the individual plant when heav- ily cropped by species such as bison. Regrowth is rapid following summer rains. (Photograph by F. L. Knopf.) of a native ungulate by a domestic ungulate in areas with low grazing pressure because of (Hartnett et al. 1997). soil conditions or availability of water. The black-tailed prairie-dog is defi nitely Grassland bird assemblage.—Several species of underappreciated in its historical role as a grazer grassland birds—Mountain Plover (Charadrius on the shortgrass prairie. This species occurred montanus), Baird’s Sparrow (Ammodramus bair- across all of Nebraska, Kansas, and Colorado. dii), Lark Bunting (Calamospiza melanocorys), (Lewis and Clark collected the fi rst specimen McCown’s Longspur (Calcarius mccownii), and in eastern Nebraska.) In areas today considered Chestnut-collared Longspur (C. ornatus)—are mixed-grass prairie, bison preferentially forage endemic to the Central Grasslands of North on prairie-dog towns (colonies), further enhanc- America (Mengel 1970), so these species evolved ing the pressure on taller grass species (Coppock within a grazed ecosystem. Some species (such et al. 1983). The sum eff ect was that the southern as Mountain Plover and McCown’s Longspur) Great Plains were noted for their monotony of occur in areas of intensive grazing, whereas vista by Mark Twain and others, which further others prefer ecotones of less intensive grazing challenges the idea of a grazing mosaic (Hart (Lark Bunting and Chestnut-collared Longspur; and Hart 1997). The intense grazing pressure Knopf 1996b). Still other species—such as on the southern Great Plains favored a fl oristic Cassin’s Sparrow (Aimophila cassinii)—are homogeneity of the grasslands (Milchunas et tolerant of, and probably require, shrub incur- al. 1988, Vinton and Collins 1997), so that the sion into prairie. “mosaic” was dominated by a single type of Avian population declines from historical grassland (shortgrass prairie), with smaller levels on the shortgrass prairie are intuitively “decorative tile” inserts of tall grass and shrubs obvious. Populations were certainly reduced CONSERVATION OF GRASSLAND BIRDS 19 as a result of the extensive fragmentation of the birds, and management for grassland species prairie as it was converted to agricultural crops, occurs with varying degrees of att ention. especially cereal grains, since the late 1800s. Managing habitat for grassland birds.— More recently, however, BBS data indicate Ecological restoration methods have not been continued, widespread declines of endemic developed specifi cally for the shortgrass prairie grassland birds. The widespread nature of as they have for the tallgrass (true) prairie. The these declines across species argues for broad CRP most closely approximates an eff ort to regional changes in the shortgrass prairie or manage for grassland birds on the Great Plains, across wintering areas since the mid-1960s albeit secondarily. Under this program, farmers (Knopf 1994). are paid to take land out of production to pre- The Mountain Plover is the most intensively vent soil erosion and to create wildlife habitat. studied of the endemic birds of the shortgrass A total of 8,044,346 ha of private lands is reg- prairie. The proposal to list it as a Threatened istered in the program across the 10-state area, Species under the auspices of the Endangered with 4,708,301 ha in the current shortgrass- Species Act (U.S. Fish and Wildlife Service 2002) prairie region of the southern plains (Allen and identifi ed fi ve major threats to the continental Vandever 2005). Thus, grassland conservation is population: (1) conversion of native grass- infl uenced more by CRP on private lands than lands to agriculture on the breeding grounds, by management of public lands within any (2) destruction of nests by certain agricultural single agency. practices, (3) historical conversion of native Despite the massive acreage enrolled in CRP, grasslands on wintering grounds, (4) conse- however, fi elds within most of the historical quences of rangeland management (standard- shortgrass prairies have been planted primarily ized grazing, reduction of prairie-dog [Cynomys to taller native or tame grasses that may have spp.] populations), and (5) confl icts arising from historically occurred in local patches, but not the development of mineral-extraction projects over broad areas. Whereas response to CRP (Knopf and Wunder 2006). These threats, indi- by the more widespread grassland species has vidually and cumulatively, surely infl uence been favorable in the northern portion of the populations of the other Central Grassland Great Plains (Johnson and Igl 1995), Central endemics as well. Grasslands endemic species that breed in Current habitat for grassland birds.—Unlike the northern Great Plains and winter on the other areas of native grasslands in North southern Great Plains have not colonized CRP America, the shortgrass prairie has a relatively fi elds, probably because these species require large component of public lands. Following the shortgrass habitats. Populations of species such devastation of the Dust Bowl, many parcels as Baird’s Sparrow, Lark Bunting, and Chestnut- were repurchased by the federal government collared Longspur have declined signifi cantly and assigned to the Soil Conservation Service. during the CRP era (1986–2002; Sauer et al. A total of 1,548,000 ha was subsequently turned 2003). The organization Environmental Defense over to the U.S. Forest Service in 1954, to be is working with avian biologists, range ecolo- managed as 19 new national grasslands begin- gists, and federal agencies to help refi ne CRP ning in 1960 (West 1990). Seventeen of these management programs, including the proper national grasslands are on the historical south- grazing of Great Plains grasslands. To date, ern Great Plains. Additional properties are grazing of CRP lands has been permitt ed only managed by the Department of Interior through within the context of drought (“disaster”) relief, the Bureau of Indian Aff airs (8,033,992 ha), and not as a management tool. Bureau of Land Management (4,930,503 ha), Given that restoration practices have not Bureau of Reclamation (275,190 ha), Fish and been developed for the shortgrass prairie, Wildlife Service (713,993 ha), and National Park management practices for birds in this region Service (53,883 ha), and by the Department of rely more on intuition and an understanding Defense (1,434,136 ha). Collectively, ~6% of the of natural history than on information derived historical southern Great Plains is in public from experiments on how bird populations are ownership, with most of the acreage located aff ected by habitat manipulation (Johnson and disproportionately in the west. Substantial por- Igl 2001b). Fire was not a prevalent ecological tions of these lands are suitable for grassland driver in the shortgrass prairie. The endemic 20 ORNITHOLOGICAL MONOGRAPHS NO. 64 shortgrass species blue grama and buff alo grass Management of shortgrass prairie for are highly drought tolerant and maintain ~90% grassland birds faces one additional hurdle of their biomass below the surface. Thus, native not encountered elsewhere in North America. shortgrass landscapes lack adequate fuel— Grazing on public lands is almost universally because most of each plant is subterranean and opposed by environmental organizations, on because of intensive removal of aboveground the basis of studies in desert, riparian, and tissues by herbivores and high levels of wind forested landscapes of western North America. erosion of the litt er layer during the dormant Numerous studies show, however, that many season—to carry a fi re any distance, restricting of the species characteristic of shortgrass prai- the historical role of fi re as an ecological driver ries increase in density as grazing intensity and limiting the current effi cacy of fi re as a man- increases (although this relationship depends agement tool to local use only. on soil conditions and seasonal rainfall; Knopf Grazing is the principal management tool 1996a). Where grazing by domestic stock is to promote the shortgrass species that evolved not permitt ed across broad landscapes, these in this biome, especially as one approaches endemic species will be threatened unless the Rocky Mountains. Grazing is as critical to dense populations of native grazers are restored the health of shortgrass prairie as it is in the throughout these areas. Serengeti Plains of Africa (Sinclair and Norton- Griffi ths 1979). Without grazing, shading by Northern Plains taller (native and exotic) grasses precludes establishment and growth of the historically History of grasslands.—The northern plains dominant shortgrass species. Drought toler- include southeastern Alberta, southern Sas- ance and grazing drive shortgrass-prairie katchewan, and southwestern Manitoba in health, and endemic grassland birds generally Canada and much of Montana, North Dakota, exploit niches created by diff erent intensities South Dakota, and northeastern Wyoming in of grazing at local and regional scales (Knopf the United States. Shaped by glacial deposits, 1996b; Fig. 8). Unfortunately, neither experi- the northern plains are fl at to rolling and mental nor rigorous observational data are are dott ed with intermitt ent wetlands (prai- available to make specifi c recommendations rie potholes). Precipitation is generally low, about how grazing can be managed to favor evaporation exceeds precipitation, and periodic these species. droughts occur (Gauthier et al. 2003). Rainfall

Fig. 8. Distribution of endemic birds of prairie uplands in relation to grassland type and historical grazing pressure across the central plains. (Reprinted from Knopf 1996b.) CONSERVATION OF GRASSLAND BIRDS 21 increases from west to east and south to north were usually relatively small (Higgins 1984), (from 20 cm in the west to ~45 cm in the east and both human and lightning-caused fi res and north), which creates diff erent prairie land- contributed to the historical fi re regime (Romo scapes: small blocks of fescue, and large zones 2003). The lightning season was mid-May to of mixed-grass, moist mixed-grass, and aspen mid-September, but fi res set by First Nations (Populus spp.) parkland. Parkland is the transi- people were most common in April, September, tion zone between grassland and forest. Mixed- and October (Higgins 1986). grass prairie is a combination of grasses of short Grassland bird assemblage.—Twenty-six spe- and intermediate height, but the species of cies of obligate grassland birds (sensu Vickery intermediate height contribute more biomass, et al. 1999b) breed in the northern mixed-grass except in heavily grazed areas. Shrubs may be prairie. Nine of these are endemic to the Central scatt ered in the grass or form dense stands. The Grasslands of North America (Mengel 1970). mixed-grass prairie is bordered by tall grass to Twenty-two of the 25 obligate grassland species the east and trees to the north. for which we have suffi cient data on population Historically, lack of moisture and extreme trends (and 8 of 9 Central Grassland endemics) variability in moisture maintained grass as the are declining (Sauer et al. 2005). dominant vegetation (Samson et al. 2004), so it Even the tallest vegetation required by Central was the primary driver in this region. Amount Grassland endemics is lower than that generally of precipitation, in combination with soil qual- available in eastern grasslands. Sprague’s Pipits ity and the secondary drivers of grazing and (Anthus spragueii), and Baird’s Sparrows need (to a lesser degree) fi re, determined the extent grasses 10–30 cm in height and avoid areas with of grass, the height and density of the standing taller grass cover, woody cover, or excessive lit- crop of herbage, and amount of litt er and shrub ter (>4 cm depth; Robbins and Dale 1999, Green incursion. Because each factor varied tempo- et al. 2002). Mountain Plovers use very short rally, spatially, or both, the historical northern cover and are oft en associated with prairie-dog plains were dynamic. towns. McCown’s and Chestnut-collared long- All the northern plains area was grazed inter- spurs prefer low to moderately low cover. Many mitt ently by bison, pronghorn, and elk. Much of prairie birds need some heterogeneity. Marbled it was also grazed by lagomorphs, Richardson’s Godwits (Limosa fedoa) need diff erent cover ground squirrels (Spermophilus richardsonii), and heights for feeding, nesting, and brood rearing black-tailed prairie-dogs. The large number of (Ryan et al. 1984). Burrowing Owls need a mix of bison and their willingness to forage far from short and moderate grasses, but also need holes water meant that areas were probably grazed created by burrowing mammals for nesting severely and fairly uniformly. However, par- and escape. Lark Buntings, Brewer’s Sparrows ticular sites had one to eight years of recovery (Spizella breweri) and Clay-colored Sparrows (S. before a herd returned (Malainey and Sherriff pallida) require some shrubs. Ferruginous Hawk 1996). In contrast to the short-grass prairie, (Buteo regalis) can hunt and nest in a variety where grazing created a highly homogeneous of grassland conditions with or without trees. stand, more localized grazing by bison in the Horned Larks and Western Meadowlarks toler- northern plains probably resulted in a mosaic of ate a broad range of grassland conditions. large patches in all stages of renewal. Seasonal Current habitat for grassland birds.—The most changes in amount and type of forage con- obvious and important cause of bird population sumed by bison (Plumb and Dodd 1993) may declines is habitat loss. Reduction in rangeland have created other subtle diff erences between is followed by population declines in grass- patches. land birds (Murphy 2003), and populations Fire was important in holding back tree and generally are not declining in areas with more shrub invasion in the fescue, parkland, and moist rangeland (Veech 2006). In Canada, ~14 million mixed-grass. Intervals between fi res varied with hectares (30%) of native grassland is still intact soil type, moisture, and grazing. The average (Gauthier and Wiken 2003); the proportion return interval was probably 6 years in North remaining varies among provinces (Alberta, Dakota (Madden et al. 1999) and areas with 43%; Saskatchewan, 24%; Manitoba, 21%) and by similar moisture, and 10 to 26 years in Montana prairie type. In the United States, estimates for (Umbanhowar 1996) and other dry sites. Burns the historical and remaining cover of mixed grass 22 ORNITHOLOGICAL MONOGRAPHS NO. 64 are not available for all states. Samson and Knopf 2000). Many grassland bird species occur (1994) estimate that North and South Dakota less frequently when woody cover increases historically had 13.9 and 1.6 million hectares of (Robbins and Dale 1999, Green et al. 2002, Grant mixed grass, respectively, and that 28% of North et al. 2004, Ahlering 2005) or avoid nesting near Dakota prairie is intact. it (Davis 2005). Shrubs may provide cover for Governments encouraged sett lement by rodents that prey on nests of open-country birds off ering land and incentives to those willing (With 1994). Also, intensive livestock grazing to turn over the soil and plant crops. All but can reduce the health and vigor of the plant the poorest soils and steepest slopes were con- community, resulting in range conditions (rated verted from grass to grain or introduced forage “poor” or “fair” for livestock) that are less likely with associated roads, preferentially eliminat- to att ract some endemic bird species (Robbins ing grassland with the greatest primary pro- and Dale 1999; Fig. 9) and less able to sustain ductivity. Grassland birds disappear or decline grassland birds during periods of drought once the native cover is removed (Johnson and (George et al. 1992). Reduced range condi- Schwartz 1993a, b; McMaster and Davis 2000) or tion is a serious and pervasive problem, with replaced with hay (Dale et al. 1997, McMaster more than half of Canadian prairie grassland et al. 2005). Also, grassland birds nesting in estimated to be in less than “good” condition crops (Lokemoen and Beiser 1997) or hay (Dale (Prairie Farm Rehabilitation Administration et al. 1997) have low productivity. Agricultural 2000). In addition, because catt le are confi ned departments in both nations encouraged by fences, they may graze sites annually rather farmers to “improve” pastures by replacing than periodically, creating a landscape with a native plant species with introduced species far more uniform height and density of grass like crested wheatgrass (Agropyron cristatum). than would have resulted from periodic grazing Several endemic bird species use planted by bison. Both of the extreme ends of the height- pastures less frequently than native pasture and-thickness spectrum are less common, as are because it is structurally diff erent, particularly the associated birds (Knopf 1994). For example, in the litt er layer (Sutt er and Brigham 1998, prairie-dog towns, characterized by very short Davis and Duncan 1999). Chestnut-collared vegetative cover and a high proportion of bare Longspurs sometimes fi nd crested wheatgrass ground, occupy only a fraction of their original att ractive but experience lower productivity estimated distribution (Wuerthner 1997), which than on native range (Lloyd and Martin 2005). means reduced success for short-cover special- Although most habitat loss occurred during ists such as Burrowing Owls (Desmond et al. sett lement, grassland continues to be converted 2000). to urban and suburban sett lement (Hansen et Additional factors (invasive plants, roads, al. 2005), and crops (Brown et al. 2005: fi g. 2) or energy extraction, and habitat fragmenta- other cover. Exurban development (6–25 homes tion) have changed the quality of remaining per square kilometer) is the fastest growing form habitats and are associated with declines in of land use in the United States (Hansen et al. occupancy or productivity. Invasion by exotic 2005), with sett lement area increasing by ≤20% plants (Wilson and Belcher 1989, Robbins and in some parts of the northern plains (Brown et Dale 1999, Scheiman et al. 2003, Grant et al. al. 2005: fi g. 2). Native species (including birds) 2004) reduces avian occupancy of grassland. have decreased reproduction and survival near Two common invaders, crested wheatgrass houses, largely because development alters and smooth brome (Bromus inermis), result in habitats and increases disturbance and preda- changes to structure (e.g., amount of standing tion (Hansen et al. 2005). dead grass; Henderson and Naeth 2005) or Changes in grassland conditions may be function (e.g., litt er decomposition rates; Ogle almost as important as loss of habitat. The et al. 2003). Roads and trails are implicated in remaining prairie has lost much of its dynamic dispersal of exotic species (Larson et al. 2001). nature. Fire has been suppressed, allowing trees Roads are also associated with direct mortal- and shrubs to invade grassland in all but the ity of birds (e.g., 20–37% of Burrowing Owl driest areas. For example, aspen is expanding mortality; Haug et al. 1993) as well as changes at 0.5–5% year–1 on black soils in prairie Canada in habitat and ecological function (Forman (Prairie Farm Rehabilitation Administration 2000, Trombulak and Frissell 2000). Songbird CONSERVATION OF GRASSLAND BIRDS 23

Fig. 9. A fenceline contrast in mixed-grass prairie in southern Alberta, near the Little Bow River. The field on the left is managed with a rotational system for winter grazing. There is substantial between-season carryover, and the site is in good range health. It would sustain some individuals of many species, including general- ists like Horned Lark and Western Meadowlark; a few species that like low cover, such as Chestnut-collared Longspur; and a variety of those needing moderate to relatively tall cover. The field on the right has been grazed intensively in a season-long system and would support mainly generalists and low-cover-specialist birds. (Photograph by Barry Adams, Alberta Sustainable Resource Development.) numbers were 20–50% lower within 100 m of linked to impaired habitat function and qual- gravel roads in Saskatchewan (Sutt er et al. 2000) ity but also includes edge, minimum area, and and Wyoming (Ingelfi nger 2001). Assuming a isolation eff ects on abundance and productiv- similar zone of eff ect, Forman (2000) estimated ity. Fragmentation or area sensitivity has been that 16.7% of rural areas in the United States are implicated in some tallgrass situations, but fi nd- infl uenced by roads. The zone of eff ect may be ings vary by region and species (Johnson and larger, because grassland songbirds continued Igl 2001a). Regionally, area sensitivity was doc- to increase with distance from roads out to umented in some species using North Dakota 2 km (Koper and Schmiegelow 2006b). Energy CRP (Johnson and Igl 2001a) and Saskatchewan extraction is a common but litt le-studied activ- native grass (Davis 2004) and planted cover ity (Fig. 10). Birds can respond to well pads and (McMaster and Davis 2000). Abundance was pipelines themselves (Gratt o-Trevor 2000) or to bett er explained for most species by distance to associated noise (Habib 2006), roads, invasive edge than by patch size in Saskatchewan (Davis species, and traffi c (Lyon and Anderson 2003). 2004) and Alberta (Koper and Schmiegelow Greater Sage-Grouse (Centrocercus urophasia- 2006a). Abundance was unrelated to the amount nus) avoided high-density well areas (Holloran of grassland in the surrounding landscape 2005), and disturbance at leks kept female (McMaster et al. 2005, Koper and Schmiegelow Sharp-tailed Grouse (Tympanuchus phasianellus) 2006a). With a few exceptions (Grant et al. 2006), from visiting (Baydack and Hein 1987). songbird nest success was not related to patch Fragmentation of habitat involves many of size (Davis 2003, Davis et al. 2006), distance to the already-mentioned factors (range condition, edge (Koper and Schmiegelow 2006a), or the invasive species, roads, and energy extraction) nature of the surrounding landscape (McMaster 24 ORNITHOLOGICAL MONOGRAPHS NO. 64

Fig. 10. Energy-extraction activity in one portion of the northern plains. Each small dot represents an oil or gas well (Source: Alberta Energy Utilities Board and Saskatchewan Industry and Resources). The extent of grassland appears as background (Natural Resources Canada, GeoGratis: www.geogratis.cgdi.gc.ca; map cour- tesy of Olaf Jensen, Canadian Wildlife Service). et al. 2005, Davis et al. 2006), though nest for Environmental Cooperation and The Nature parasitism increased with fragmentation in one Conservancy (Karl and Hoth 2005). study (Davis and Sealy 2000). The most important goal of habitat manage- The last reason for declines is direct losses ment for grassland birds is to prevent further att ributable to predation, fi eld operations in losses of native grasslands. About 30% of crops or forage, road kills, air strikes (Dolbeer Canadian prairie grassland is in private hands, 2006), and pesticides (Mineau and Whiteside 7% is controlled by the federal government, and 2006). Fragmentation, roads, pesticides, graz- 63% is controlled by provincial, tribal, and other ing management (Desmond 2004), and invasion levels of government (Gauthier et al. 2003). by exotics and shrub are also relevant during Much public land is in community pastures migration and on the wintering grounds. or grazing leases. About 5.3% of the prairie Managing habitat for grassland birds.— is set aside for conservation, and most (63%) According to Rodriguez (2002), the mechanisms protected sites are >1,000 ha in size (Gauthier driving declines may be complex, but the and Wiken 2002), which is the threshold for conservation eff ort can be simple: concentrate “minimum viable area” (Samson et al. 2004). eff orts where birds are most abundant and work Grassland ownership in the U.S. portion of the from there. We know where high-abundance Great Plains is estimated to be 84% private, 7% areas are, thanks to the BBS, Grassland Bird federal (with the Bureau of Land Management Monitoring (Dale et al. 2005), Conservation Data and U.S. Forest Service managing the major- Centers, and individual research projects. These ity), and 9% state, municipal, county, or tribal areas, not surprisingly, coincide with large government (Gauthier et al. 2003). Separate stretches of grassland in eight “ecologically fi gures for the northern portion of the plains signifi cant areas” identifi ed by the Commission were not available. The northern plains are, in CONSERVATION OF GRASSLAND BIRDS 25 many ways, decimated and their functioning and Vandever 2005). The plant species and impaired, but with 25–30% of the original grass- strains chosen are rarely native to the region. land remaining and pieces as small as 18 ha Grazing and haying are not permitt ed except of conservation value (Davis et al. 2006), we under emergency circumstances. The total area cannot hope to buy or otherwise secure all the in Canada’s Permanent Cover Program (PCP) remaining grassland through purchase or ease- is 518,000 ha (Gauthier et al. 2003). Introduced ment. Scrutiny and adjustment of policy and plants are sown, and the cover may be grazed or legislation at federal, state or provincial, and hayed. Most endemic birds occur in low num- local levels are necessary to eliminate remain- bers in both programs (Johnson and Schwartz ing incentives to break up grasslands. 1993a, b; McMaster and Davis 2000). A com- Maintaining or rehabilitating the integrity of parison of the densities or rankings of birds on remaining grasslands is also critically impor- CRP land (Johnson and Schwartz 1993a, b) with tant. Refuges and sanctuaries are the only sites estimates on PCP land (D. G. McMaster unpubl. likely to be managed at historically appropriate data) showed that six of eight primary endem- intervals. Sustained rest in mixed-grass prairie ics were more common on the latt er. Only Lark did not occur historically and is not benefi cial Bunting was more common on CRP than on PCP for primary endemic grassland birds, because land. Avian productivity is as good on CRP land the increased height and thickness of grass, as it is on Waterfowl Production Areas, however accumulated litt er, or expanded shrub cover (Koford 1999). The PCP has been replaced by will render sites unatt ractive to specialized the Greencover Canada Program (Agriculture grassland birds. Application of natural drivers and Agri-Food Canada 2005) and will continue of grazing, and to a lesser degree burning, at to allow agricultural use that benefi ts grassland appropriate intervals should maintain the broad birds. It could be improved with date restric- variety of grassland conditions for the full suite tions on haying to increase productivity of birds of grassland birds historically associated with (Dale et al. 1997, McMaster et al. 2005). mixed-grass prairie. The variation in soil and In summary, while pursuing opportunities moisture across the northern plains makes it for protection, we must concentrate most of our impossible to off er blanket prescriptions (e.g., eff orts on extensive activities like policy reform, burn every six years, graze at a rate of 10 ha farm programs, demonstration projects, market- cow–1) to benefi t a given bird species (Kantrud ing of “eco-products,” and extension and other 1981, B. C. Dale et al. unpubl. data). Madden et forms of education to encourage retention of al. (2000) suggest using a range of acceptable native prairie and restoration of range condition vegetation measurements to guide manage- while encouraging creation of new grass habi- ment. Land managers then choose which man- tats and best practices on crops and tame for- agement tool and application rate would create age. The U.S. Farm Bill and the new Canadian those conditions in their area. Agricultural Farm Policy (Agriculture and Agri- Over much of this region, grazing is the land Food Canada 2005) are mechanisms for delivery use most compatible with long-term main- of additional cover and Good Management tenance of healthy grasslands and bird com- Practice incentives. The latt er off ers a dynamic munities. Moderate or light grazing maintains opportunity, because it incorporates farm plan- or improves range condition (Holechek et al. ning and a series of practices (reviewed annu- 1999), and sites in good condition support more ally) whose costs are off set. As we obtain more grassland bird species (George et al. 1992). information along the lines of Davis (2004) or Large fi elds are more likely to be heteroge- Fletcher et al. (2006), we can target these activi- neous, because of variety in topography and ties more precisely and modify our advice, but distance to water (B. C. Dale et al. unpubl. data, we must not delay our collaborative activities Renfrew and Ribic 2002, Fontaine et al. 2004, until we have all the answers. Koper and Schmiegelow 2006b). We need to work with other disciplines to Restoration of cover with regionally appro- make our biological fi ndings economically priate native grasses may be very benefi cial, relevant (Theobald et al. 2005). Good graz- but, for economic reasons, it is not widespread. ing management is consistent with profi ts The total area in CRP in the northern plains for producers (Holechek et al. 1999, Prairie region of the United States is 3,336,045 ha (Allen Farm Rehabilitation Administration 2000), 26 ORNITHOLOGICAL MONOGRAPHS NO. 64 and society benefi ts not only from increases in for engaging stakeholders and building on forage production but also from build-up of soil common goals related to maintaining healthy organic matt er and sequestered atmospheric prairie (Nernberg and Ingstrup 2005). carbon (Conant et al. 2001). Minimum-tillage fi elds are bett er than conventional fi elds in Desert Grasslands terms of abundance, nest densities, and produc- tivity of birds (Martin and Forsyth 2003) and History of grasslands.—The grasslands of off er producers improved economics through northern Mexico and the southwestern United reduced fi eld operations and maximum use of States are generally referred to as “desert grass- limited moisture. Conservation objectives can lands” (Rzedowski 1975, McClaran 1995; Fig. be achieved with litt le economic cost or confl ict 11). The geographic extent of this grassland (Polasky et al. 2005). type basically coincides with the Chihuahuan Delivery of the North American Bird Desert Ecoregion, which covers the Central Conservation Initiative through North American Plateau of Mexico south to approximately Waterfowl Management Plan (NAWMP) joint the Transvolcanic belt and is bordered on the ventures has been hailed as an opportunity east and west by the Sierra Madre Oriental for conserving grassland birds (Brennan and Occidental, respectively, north to west and Kuvlesky 2005), but cover programs for Texas, southern New Mexico, and southeast- waterfowl in the northern plains have limited ern Arizona. As the name implies, the main benefi ts for high-priority grassland birds (Dale ecological driver of desert grassland systems and McKeating 1996), and ducks do not always is drought. Fire, however, played a role in act as a conservation surrogate for other avian maintaining some areas of desert grasslands species in the mixed-grass prairie (Koper and in the past (Humphrey 1958, Bahre 1991). The Schmiegelow 2006b). The NAWMP’s recent frequency of fi res in prehistoric times is diffi cult emphasis on protection of native habitats and to determine for desert and other grasslands, on policy scrutiny is, however, benefi cial to but several authors estimate that fi res may grassland birds. Also, the Prairie Conservation have occurred at intervals of approximately Action Plan functions as an important forum 7–10 years. This estimate is based on indirect

Fig. 11. Desert grassland landscape with open-ground patches and shrubby elements of yucca in northern Chihuahua, Mexico. (Photograph by Profauna Chihuahua.) CONSERVATION OF GRASSLAND BIRDS 27 evidence such as presence and abundance of stretches of grassland from trans-Pecos Texas to woody species (Griffi ths 1910, Leopold 1924, southeastern Arizona; for example, prairie-dog Wright and Bailey 1980, Schmutz et al. 1985). towns covered an estimated 2.5 million ha in Early Spanish explorers reported that fi res were New Mexico. Federal programs in the United intentionally set by Native American tribes in States almost completely exterminated prairie- desert grasslands in Mexico and the southwest- dogs from this region by the 1960s. Numerous ern United States (Gentry 1957). Fire can have prairie-dogs, however, are still found in grass- major eff ects on desert grasslands. It eliminates lands in northwestern Mexico (Ceballos et al. cover in the short term, but may reduce the den- 1993), where there have been few large-scale sity of woody species in the long term. Saab et eradication programs. The largest prairie- al. (1995) argued that the suppression of fi res in dog complex in North America is found at this system produced, through increased woody Janos-Nuevo Casas Grandes in northwestern plant cover, the drastic changes in ecosystem Chihuahua, Mexico; it covers an estimated structure and function currently observed 55,258 ha (with one colony covering 34,949 ha; throughout desert grasslands in Mexico and Ceballos et al. 1993). The distribution of the the southwestern United States. Dinerstein et al. Mexican prairie-dog in Coahuila, Nuevo Leon, (2000) estimated that grasslands have decreased San Luis Potosi, and Zacatecas has decreased between 25% and 50% because of the spread of signifi cantly from an estimated 1,500 km2 to shrublands in the region. only 290 km2 in 1999 (Scott -Morales et al. 2004). Grazing by native herbivores may have been Most of the destruction has resulted from con- even more important than fi re in preventing version of prairie-dog colonies to agriculture woody shrubs from spreading in desert grass- production and continues to the present day. lands (Weltzin et al. 1997). The primary natural Prairie-dogs have a substantial infl uence grazers of desert grasslands were black-tailed on grasslands. By constantly clipping the veg- prairie-dogs in the United States and northern etation to maintain an unobstructed view of Mexico; Mexican prairie-dogs (C. mexicanus) in the landscape, they prevent shrub and other central Mexico; and, to a lesser extent, bison and woody species from invading. Koford (1958: pronghorn (Anderson 1982, Saab et al 1995). 59) found that eradication of prairie-dogs usu- Bison are reported to have roamed the region ally results in the spread of mesquite, convert- intermitt ently, being present in a particular area ing grassland to shrubland, and that “many only sporadically in some years, apparently as old timers in Texas and Oklahoma att ribute a result of irruption-type movements from the the great increase in mesquite on grasslands Great Plains. The net eff ect of these sporadic during the past century to the extermination of irruptions of bison on the native grasslands and prairie dogs.” Thus, prairie-dog eradication may overall landscape of the region is not known, explain why so much of the desert grassland but probably was not strong (Parmenter and has been converted to mesquite scrub (Weltzin Van Devender 1995, Monger et al. 1998). Also, et al. 1997). By contrast, areas with prairie-dog pronghorn were found in large numbers in the colonies in Chihuahua have remained open southwestern United States (Parmenter and grassland (Ceballos et al. 1993, Manzano-Fischer Van Devender 1995). Although pronghorn are et al. 1999). The role of prairie-dogs in preventing primarily forb-foragers or browsers rather than shrub invasion is consistent with evidence that grazers, in many areas of desert grasslands, the there was never enough fuel in desert grasslands most abundant plant species can at times be to permit extensive burns (Van Auken 2000) and forbs. that mesquite is more resistant to fi re damage The frequency and intensity of grazing in than some species of semidesert grass, such as desert grasslands before the introduction of black grama (Bouteloua eripoda; Buffi ngton and large number of domestic grazers starting ~450 Herbel 1965). years ago is not well known, but it is clear from Grassland bird assemblage.—Many of the grass- historical descriptions that prairie-dogs were land bird species that breed in the desert grass- mostly responsible for the overall structure lands of Mexico and the southwestern United of vast areas of desert grassland communities States also breed farther north in the prairies (Parmenter and Van Devender 1995). Until of the United States and Canada (Peterson the 1930s, prairie-dog towns covered large and Robbins 1999). These include Horned 28 ORNITHOLOGICAL MONOGRAPHS NO. 64

Lark, Savannah Sparrow, and Grasshopper Desert grasslands are structurally short and Sparrow. Other species that nest in the Great support a lower avian species-richness than Plains are winter residents in desert grasslands peripheral areas (Mengel 1970), which are the (e.g., Ferruginous Hawk, Mountain Plover, transition zones with more structurally com- Long-billed Curlew (Numenius americanus), plex environments imbedded in the grasslands, Vesper Sparrow, Lark Bunting, McCown’s and such as riparian woodlands, mountain slopes, Chestnut-sided longspurs, and Eastern and and adjoining shrublands. Prairie-dog colo- Western meadowlarks). Several species listed nies support higher diversity and densities of as birds of conservation concern by the U.S. shortgrass-prairie birds than adjacent grassland Fish and Wildlife Service, such as Sprague’s areas without prairie-dogs (Agnew et al 1986, Pipit and Baird’s Sparrow, are concentrated Desmond 2004). Some species are particularly in this region during winter. A few grassland frequent in prairie-dog colonies (e.g., Mountain species are endemic or nearly endemic to the Plover and Ferruginous Hawk; Fig. 12), whereas Chihuahuan Desert of northern Mexico and the others are common on prairie-dog colony edges adjacent United States (e.g., Bott eri’s Sparrow (i.e., sparrows [Spizella spp.], Lark Buntings). [Aimophila bott erii] and Rufous-winged Sparrow Bird surveys in the Janos-Nuevo Casas Grandes [A. carpalis]). Populations of the northern prairie-dog complex of Chihuahua revealed Aplomado Falcon (Falco femoralis septentrio- that Horned Larks and Lark Buntings were nalis) have historically (Oberholser 1974) and abundant and that several other grassland spe- recently (Young et al. 2004) been found in cialists (Ferruginous Hawk, Mountain Plover, grasslands of the northern Chihuahuan Desert Long-billed Curlew, Burrowing Owl, longspurs (Texas, New Mexico, and Chihuahua). The only [Calcarius spp.], and meadowlarks [Sturnella avian species truly endemic to this grassland spp.]) were common (Manzano-Fischer et al. system is Worthen’s Sparrow (Spizella wortheni; 1999). Phillips 1977), which is considered threatened With a few notable exceptions, shortgrass- by BirdLife International (Byers et al. 1995). dependent birds are the least understood of It occupies shrubby grassland habitats and is North American birds in both breeding and found consistently, though in low densities, at wintering areas (Phillips 1977). This is particu- the edges of prairie-dog colonies in Coahuila, larly true for northern Mexico, where detailed Nuevo Leon, and San Luis Potosi (Garza de studies of desert grassland avifauna have taken Leon et al. 2007). place only during the past two decades except Although large tracts of desert grassland in a few areas, such as the Mapimi Biosphere remain, many species that nest and winter in this Reserve. For example, breeding by Mountain type of environment are declining. Results of the Plovers was documented only recently in colo- North American BBS indicate that many of the nies of Mexican prairie-dogs in northern Mexico species that breed or spend the winter in desert (Desmond and Chávez-Ramírez 2002, González grasslands have had overall population declines Rojas et al. 2006). in North America since the mid-1960s (Knopf The patt erns of occurrence for individual 1994). Population declines can be att ributed to species and large concentrations of birds in spe- several factors, including loss and fragmentation cifi c regions of the desert grassland are highly of habitat. Loss of grasslands in this region is dynamic and highly variable from year to year att ributable not only to conversion to shrublands (Raitt and Pimm 1977), probably because of the following elimination of natural grazers and variability in rainfall patt erns and food produc- fi re, but also to the transformation of some areas tion. The same area may have large concen- for agricultural purposes. Prairie-dogs have trations of winter-resident sparrows in some long been persecuted by catt le ranchers in both winters and none in other winters (Desmond Mexico and the United States, leading to their 2004, F. Chávez-Ramírez pers. obs.). This pat- elimination in many regions and diminishing tern was observed in a Christmas Bird Count their infl uence in maintaining desert grasslands in northwestern Chihuahua, where counts of free of woody invaders. Even where prairie-dogs sparrows (Spizella spp.) varied from <2,000 to remain in some areas of Chihuahua, severe over- >13,000 in successive years (Dieni et al. 2003). grazing by livestock results in a habitat with few Grassland bird communities are also character- grassland birds (Desmond 2004). ized by high turnover rates between breeding CONSERVATION OF GRASSLAND BIRDS 29

Fig. 12. Mountain Plover in Mexican prairie-dog colony, La Soledad, Nuevo Leon, Mexico. Short grassland vegetation can be seen within prairie-dog colony in contrast to adjacent desert scrub. (Photograph by Rogelio Hernandez.) and wintering periods (Webster 1964, Raitt and grasslands are the least represented of vegetation Pimm 1977, F. Chávez-Ramírez pers. obs.). communities in these protected areas (F. Chávez- Current habitat for grassland birds.—Dinerstein Ramírez pers. obs.). Also, most designated pro- et al. (2000) estimated that ~20% of the tected areas in Mexico allow livestock grazing. Chihuahuan Desert region is currently grass- In Mexico, a proportion of the grasslands and land. The largest expanses of contiguous desert other rural lands is held as communal proper- grasslands are found in Arizona, New Mexico, ties called ejidos. An ejido is generally defi ned and Texas, and the amount decreases southward as a population center whose inhabitants have through the Mexican states. The condition of the common use of a designated area, generally remaining tracts of grassland is variable but is rangeland or agricultural areas. Most ejidos are generally poor because of continuous overgraz- rural communities that use the land primarily ing. The best-conserved remaining blocks of for grazing catt le and goats, but also for small- desert grassland are in central Chihuahua. Most scale agricultural plots. The proportion of land desert grassland areas are privately owned catt le held as ejidos is greater in the southern Mexican ranches. In the United States, some desert grass- states (40% in Durango, Zacatecas, and San lands are protected in reserves and experimental Luis Potosi) than in the northern areas (15% in ranges (e.g., Jornada Experimental Range, Santa Chihuahua and Coahuila). Rita Experimental Range, and Appleton-Whitt le A continual and gradual decline in grassland Research Ranch). Similar reserves and state or condition has occurred, with litt le concerted federal experimental ranges occur in Mexico eff ort to reverse the trend. Eff orts to increase (La Campana, Mapimi, and Cuatro Cienegas). productivity of desert grasslands have led to However, combined, reserves and grassland introduction of nonnative grasses, and eff orts research stations represent a small proportion to restore highly degraded sites with native of the area dominated by desert grasslands. In grassland species have not been successful the United States, it is estimated that 7.9% of the (Griffi ths 1907, Roundy and Biedenbender Chihuahuan Desert (roughly equal to the extent 1995). Land-reclamation eff orts have been of desert grasslands) is under some sort of pro- more successful when using nonnative grasses tection (DellaSala et al. 2001). In Mexico, the esti- or native shrubs and cacti. Although success- mated area under a protected designation within ful establishment of native shrubs may reduce the Chihuahuan Desert is <2%. The actual area soil erosion and stabilize the soil, it has the net of protected grasslands is much less, because eff ect of converting areas previously dominated 30 ORNITHOLOGICAL MONOGRAPHS NO. 64 by grasslands into shrublands, leading to elimi- reduction of fi re frequency, long-term climate nation of potential habitat for grassland birds. changes, and increasing concentrations of atmo- Most grassland-restoration experiments are spheric carbon dioxide, “widespread eradication conducted as research projects on small plots of prairie dogs may have been both necessary using expensive and labor-intensive methods, and suffi cient to enable post-sett lement increases so it is unlikely that large restoration activities in shrublands and woodlands.” This contrasts will be undertaken in the near future. with the widespread view that there were so Managing habitat for grassland birds.— few native grazers in desert grassland that this Management of desert grasslands focuses on system cannot sustain grazing by domestic stock its use as pasture for livestock. Low-intensity (Saab et al. 1995). The remaining prairie-dog col- grazing does not appear to negatively aff ect onies in Mexico should be protected and studied the birds that depend on these grasslands, but to determine whether grazing by prairie-dogs higher-intensity grazing by catt le has a negative can help maintain desert grasslands, providing eff ect on grassland cover and on some species of habitat for grassland birds and permitt ing sus- grassland birds (Krueper et al. 2003, Desmond tainable catt le production. Grassland restoration 2004). Any management recommendations in the southwestern United States may be diffi - for maintaining desert grasslands will have to cult without the reintroduction of this keystone focus on the intensity and level of grazing pres- species (Miller et al. 1994). sure and its eff ects on birds. More information is needed to adequately address the net eff ects General Implications for Grassland Bird of diff erent levels and timing of livestock graz- Conservation ing on grassland birds in this area. Governmental programs can promote the Although the grasslands and savannas we protection, conservation, or destruction of have discussed have distinctly diff erent climates, grasslands. Programs such as CRP are available vegetation, and bird assemblages, they share only for the U.S. portion of the desert grassland; some of the same basic conservation problems. Mexico has no similar program. However, All these ecosystems have suff ered from consid- unlike in the northern plains, where grassland erable habitat conversion, with almost complete birds use CRP fi elds extensively (Johnson and loss of tallgrass prairies, northeastern coastal Igl 1995), CRP fi elds in general have not pro- grasslands, and longleaf pine savannas. Tallgrass vided additional habitats for shortgrass avian prairies were plowed to create cropland, longleaf species. Mexico’s perverse incentives have led pine savannas have been replaced with pine to the conversion of grasslands to agricultural plantations and suburbs, and most of the coastal fi elds in areas with only marginal potential for grasslands are now industrial and residential agricultural production. Governmental pro- areas. Farming is also widespread in the mixed- grams in Mexico provide fi nancial incentives to grass and shortgrass prairies. individuals for each new area opened for agri- Even when grasslands have not been directly cultural production for staple crops, regardless transformed into grain fi elds or suburban of the soil’s potential for crop production. neighborhoods, they frequently have lost the Conservation of desert grasslands depends basic ecological processes that sustained them not only on the establishment and maintenance (Vickery and Herkert 2001). In the northeastern of protected areas devoted exclusively to grass- coastal plain, southeastern pine fl atlands, tall- land systems, but also on bett er management of grass prairies, and western aspen parklands, grazing on private land. The historical evidence fi re suppression led to the displacement of open, for dense populations of grazers (especially grass-dominated habitats by dense woody veg- prairie-dogs, but also pronghorn and bison) etation. Elimination of native grazers (especially suggests that restored desert grasslands could prairie-dogs) and fi re probably triggered a simi- sustain moderate grazing. In fact, grazing by lar process in the desert grasslands, leading to prairie-dogs could help maintain these grass- the spread of mesquite scrub. In shortgrass and lands, preventing the invasion of woody shrubs mixed-grass prairies, removal of grazers (both and trees. As Weltzin et al. (1997:761) argue, prairie-dogs and bison) and fi re resulted in the although growth of woody vegetation in desert spread of shrubs or a subtler shift in the den- grassland may be favored by such factors as sity and dominant species of grasses and forbs. CONSERVATION OF GRASSLAND BIRDS 31

Similarly, elimination of beavers resulted in property is managed. Some traditional methods the loss of fl oodplain meadows that supported of farming and ranching maintained habitat for a grassland birds and other early-successional diversity of grassland and savanna birds; range- species in fl oodplains of the eastern forest. land, fallow fi elds, hay meadows, fi eld edges, The suppression, alteration, or elimination of and orchards substituted for natural grasslands natural disturbances or ecological drivers can for many of these species. However, the steady transform grassland as thoroughly as planting progression to more effi cient use of land for pro- crops or building houses. duction of food and fi ber has tended to reduce its Similar processes seem to apply to the other suitability as breeding, migration, or winter hab- North American grasslands that we did not itat for most grassland specialists. This appears discuss. The tule prairies of the Central Valley to be the main cause of recent sharp declines in of California were maintained by the grazing of populations of grassland birds. dense populations of tule elk (Cervus elaphus nan- Grassland birds became vulnerable when nodes), giant kangaroo rats (Dipodomys ingens), their natural habitats were destroyed or dis- and pronghorns (Knopf and Rupert 1995). The rupted so that they became dependent on grasslands of the Great Valley of Virginia were artifi cial habitats. Top priorities for conserva- heavily grazed by bison and elk and appar- tion of grassland birds are preservation and ently frequently burned by Native Americans restoration of remaining native grassland. A (Kercheval 1850). The seasonally fl ooded, open goal in all three of the countries that we have “prairies” of the Florida Everglades (where discussed here (Canada, the United States, the endangered Cape Sable Seaside Sparrow and Mexico) should be removal of direct and [Ammodramus maritimus mirabilis]) lives) are gen- indirect incentives in government agricultural erated by periodic wet-season burns (Kushlan et programs for converting grassland to cropland. al. 1982). Midwestern oak savannas were also Moreover, the most intact natural grasslands maintained by periodic burns (Curtis 1959). should be protected as grassland reserves, as In some ecosystems, such as longleaf pine has been done in tallgrass-prairie landscapes savannas, tallgrass prairie, and desert grassland, by The Nature Conservancy and state agencies changes in ecological processes can lead to in Illinois and Missouri, and in mixed-grass rapid and substantial changes in vegetation prairies in Grasslands National Park and structure that are not easily reversed (Westoby Canadian Forces Base (CFB) Suffi eld National et al. 1989). For example, suppression of fi re or Wildlife Area in Canada. Protecting extensive removal of native grazers (or a combination of prairie-dog complexes and restoring their habi- these factors) can cause a grassland to shift to tat in northern Mexico (at Janos-Nuevo Casas a new stable state such as dense, woody veg- Grandes, Chihuahua, for example) is a particu- etation. When the original ecological processes larly high priority, because it is no longer pos- that characterized this system are restored (e.g., sible to study the ecological eff ects of extensive native grazers are reintroduced or prescribed grazing by prairie-dogs in desert grasslands in burning is implemented), the vegetation may the southwestern United States. These reserves not return to its original state (Westoby et al. could support source populations of grassland 1989, Briggs et al. 2005). Major restoration birds and, equally or more important, could eff orts, such as clearing shrubs and planting provide sources of information about the natu- native grasses, may be needed in these cases. ral processes that sustain habitats. The ultimate The grasslands of North America have been goal would be to re-establish these processes transformed so profoundly that it is surprising where they have been eliminated or inhibited. that some of the more specialized species of Where practical, managers should reintroduce grassland birds still persist. They were saved by fi re to tallgrass prairies and longleaf pine their ability to adjust to artifi cial habitats. With savannas, allow beavers to dam streams and the loss of prairies and savannas, many grass- create beaver meadows, and re-establish the land birds became concentrated in farmland and extensive grazing lawns maintained by prairie- ranchland where natural disturbances or ecolog- dogs on shortgrass prairies and desert grass- ical drivers were replaced with livestock grazing, lands. The systematic destruction of keystone mowing, prescribed burning, or plowing. Their species such as beavers and prairie-dogs is one future largely depends on how this private of the greatest and least-appreciated reasons 32 ORNITHOLOGICAL MONOGRAPHS NO. 64 for the loss of biological diversity in grassland appropriate recommendations. We need to systems. know more about the eff ects of livestock and In many grassland and savanna systems, native grazers in both of these systems, and biological diversity depends on natural pro- about the relative roles of grazing and fi re in cesses creating a patchwork of diff erent types of desert grasslands. Where sustainable practices vegetation across a large landscape. This patch- are profi table, education is the key to convinc- work is diffi cult to achieve in a small reserve or ing private landowners to adopt measures that even in a system of small reserves, so creation preserve or enhance biological diversity. The and consolidation of large grassland reserves challenge is more diffi cult, however, when should be a high priority. The goal should be “bird-friendly” practices reduce economic pro- to establish reserves that are large enough to ductivity or where economic hardship pushes maintain the diversity of habitats and species landowners into making unsustainable choices. characteristic of the full habitat mosaic that once The PCP in Canada and the CRP in the United characterized the region (the minimum dynamic States provide payments to farmers who take area), an approach that currently guides con- land out of production and convert it to grass- servation strategies of The Nature Conservancy land to conserve soil and provide wildlife habi- in the Great Plains (Samson et al. 2004). This tat. These programs have great potential for bird may require restoration or creation of natural conservation, because they involve large areas grassland around existing grassland reserves, of land. In some regions (particularly in the followed by reintroduction of natural drivers or northern plains), fi elds in these programs pro- disturbances. A large-scale strategy of this sort vide good breeding habitat for grassland birds. will require much greater cooperation among In shortgrass prairie, however, CRP fi elds are government agencies, nonprofi t organizations, usually planted in tall grass that does not att ract and private landowners. Large publicly owned endemic shortgrass-prairie birds. This problem grasslands are administered by diff erent govern- is particularly acute in the United States, where ment agencies (Samson et al. 2004), but recently grazing has not normally been permitt ed on CRP these agencies have begun to work together and land. Both programs would be more eff ective to work with other land managers through con- if they were specifi cally designed to provide servation programs such as Partners in Flight, habitat for native grassland species, permitt ing Prairie Partners, and Center for Environmental grazing where it is appropriate and banning it Cooperation. These programs have begun to where it is not; providing greater incentives to focus on conservation of grassland ecosystems contribute to the establishment of large expanses and to work across international boundaries to of continuous grassland; and encouraging the preserve breeding, migratory stopover, and win- planting and maintenance of native grass species. tering habitat of grassland birds in Canada, the In this regard, the newly established Grassland United States, and Mexico. Reserve Program of the 2002 U.S. Farm Bill may Although protection and restoration of provide greater potential benefi ts for grassland natural grasslands are important goals, they birds because it protects existing grasslands (and probably will not be suffi cient for conserva- therefore does not require the need to restore tion of some species of grassland birds. It grass), and participants retain the right to graze, is unlikely that enough large grassland and mow, or hay the land, subject to restrictions savanna reserves can be established to main- designed to protect nesting birds. tain regional populations of grassland special- North Americans could develop incentives for ists. Fortunately, these species can potentially conservation by emulating European programs be supported on working land such as farms, that make birds (and other elements of biological ranches, airports, or commercial forests. For diversity) a “farm product” (Musters et al. 2001). some habitats, such as tallgrass prairies and Incentive programs have become an integral longleaf pine savannas, researchers can already part of the agricultural support system of the provide specifi c recommendations for manag- European Economic Community (Kleij n et al. ing working land to support grassland birds 2004). Similar programs not only could sustain and other grassland organisms. For other natural diversity and protect rural landscapes, habitats, such as shortgrass prairies and desert but also could directly help support farmers and grasslands, more research is needed to develop ranchers in North America. European nations CONSERVATION OF GRASSLAND BIRDS 33 have tried various types of programs since the et al. 2004) or population densities of meadow 1970s, so North Americans can learn from both birds in fi elds in The Netherlands (Kleij n et al. their successes and their failures. 2004). A more thorough understanding of the In the United Kingdom, the steep decline in habitat requirements of these birds and a more populations of farmland birds since the mid- coordinated eff ort to restore regional landscapes 1970s led to the adoption of “agri-environment should help improve the success rate. schemes” to encourage farmers to manage their Another promising approach is to pay farm- land to provide habitat for birds that require ers for their success in supporting populations open fi elds (Vickery et al. 2004). Two majors of target species. In a pilot program in The approaches are used: Environmentally Sensitive Netherlands, farmers were paid for every clutch Areas, in which farmers in a designated geo- of young produced by meadow-dependent birds graphic region are paid to enhance landscape (Musters et al. 2001). Such an intensive monitor- or biodiversity features; and the Countryside ing program is unrealistic for most of North Stewardship Scheme (CSS), in which farmers in America, but farmers, ranchers, and forest man- any region are compensated for adopting “good agers could be paid for sustaining populations farming practices” that enhance biological of particular species. Landowners would then diversity (such as delaying mowing to prevent participate in improving habitat management destruction of nests and restrictions on grazing). methods and tailoring them to their own land. Eff orts to restore seminatural grassland have The seminatural grasslands of Europe are been hindered by two major problems: high the product of millennia of deforestation and nutrient concentrations because of intensive livestock grazing and, in most cases, we have application of fertilizers in the past, and loss litt le basis for reconstructing the natural eco- of the seed bank of grassland plants aft er many logical processes that sustained the original years of farming (Walker et al. 2004). British habitats of grassland species. In North America, ecologists therefore have been concentrating there is a bett er (if still imperfect) opportunity to on methods of “nutrient stripping” (removal restore natural grassland systems. Maintenance of nutrients with such practices as intensive and restoration of natural grassland should grazing and mowing) to reduce soil fertility so have the highest conservation priority, because that a wide variety of grassland plants can coex- natural ecosystems can provide important ist, and for sowing seeds of grassland plants to insights about the habitat requirements of compensate for the missing seed bank. grassland species. These insights can then guide Several studies have assessed the eff ects of eff orts to manage working land (especially eff orts to provide habitat for grassland birds in farmland and ranchland) where most grassland Europe. In Devon, England, Peach et al. (2001) birds nest and spend the nonbreeding season. If compared population trends of the Cirl Bunting landowners are compensated for sustaining and (Emberiza cirlus) in fi elds managed under a CSS enhancing biological diversity, eff orts to save and in control fi elds. This species is a threatened the distinctive species of open habitats could grassland specialist that recently suff ered a be compatible with eff orts to support rural severe population decline in England. The economies and landscapes. In the United States, CSS paid landowners to provide low-intensity the Conservation Security Program of the 2002 grazed grassland as summer habitat and bar- Farm Bill is a move in this direction; it is a vol- ley stubble as winter habitat. Densities of Cirl untary program that will provide fi nancial and Buntings increased substantially on CSS land technical assistance to landowners to promote and remained stable on land not covered by this conservation on private land including pasture agreement, indicating that the program success- and rangeland. Current economic pressures on fully enhanced habitat for this species. This man- producers of beef catt le to stockpile forage in agement program was developed aft er intensive pasture to replace hay cutt ing (e.g., Hitz and research on the ecology of Cirl Buntings and Russell 1998, Evers et al. 2004, Cuomo et al. 2005) focused on a single region where this species may have important advantages for grassland was concentrated (Kleij n et al. 2004). However, birds, and these practices deserve further study. less-focused agri-environment schemes have Another promising North American program is not demonstrably aff ected the rate of population sponsored by the Colorado Division of Wildlife, declines in grassland birds in England (Vickery which expended more than $1 million in 2004 34 ORNITHOLOGICAL MONOGRAPHS NO. 64 for its new Species Conservation Partnership gradients in a longleaf pine ecosystem. Auk Program to place conservation easements on 123:1110–1128. ~8,100 ha of private land (K. Morgan pers. Anderson, R. C. 1982. An evolutionary model sum- comm.). The Colorado program goes beyond marizing the roles of fi re, climate and grazing concern for the shortgrass prairies to emphasize animals in the origin and maintenance of grass- lands: An end paper. Pages 297–308 in Grasses the whole prairie ecosystem and encompasses and Grasslands: Systematics and Ecology declining species of a wide range of taxa. The (J. R. Estes, R. J. Tyrl, and J. N. Brunken, Eds.). black-tailed prairie-dog is a key component of University of Oklahoma Press, Norman. many easements because of its role as an ecolog- Askins, R. A. 1993. Population trends in grassland, ical driver in this system. Similar revolutionary shrubland, and forest birds in eastern North programs are needed to secure the ecological America. Pages 1–34 in Current Ornithology, vol. sett ing necessary to conserve the birds of native 11 (D. M. Power, Ed.). Plenum Press, New York. grasslands. Askins, R. A. 1997. History of grasslands in the northeastern United States: Implications for bird conservation. Pages 119–136 in Grasslands Acknoledgments of Northeastern North America (P. D. Vickery and P. W. Dunwiddie, Eds.). Massachusett s We thank the AOU Conservation Committ ee for Audubon Society, Lincoln. inviting us to work on this project. We especially thank Askins, R. A. 1999. History of grassland birds in J. Walters, chair of that committ ee, for his advice on the eastern North America. Pages 60–71 in Ecology organization and goals of this paper, and for his guid- and Conservation of Grassland Birds in the ance and patience during each stage of its preparation. Western Hemisphere (P. D. Vickery and J. R. We also thank T. Bidwell, E. Bollinger, J. Faaborg, S. Herkert, Eds.). Studies in Avian Biology, no Sealy, M. Winter, and an anonymous reviewer for 19. carefully reviewing draft s of this paper. Data from the Askins, R. A. 2000. 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