The Central Shortgrass Prairie Physiographic Area covers much of eastern Colorado and smaller portions of western Kansas, southwestern Nebraska, and southeastern Wyoming. Most of the land (70%) is privately owned; the remainder is under the jurisdiction of the states (22%) and the federal government (7%). Principal federal holdings are U.S. Forest Service National Grasslands: Thunder Basin in Wyoming (231,485 ha; 572,000 ac), Pawnee (78,100 ha; 193,000 ac) and Comanche (169,570 ha; 419,000 ac) in Colorado, Ogallala in Nebraska (37,800 ha; 93,400 ac), and Cimarron in Kansas (43,700 ha; 108,000 ac).

The region contains flat to gently rolling topography, with occasional canyons and bluffs. Elevations within Colorado range from about 975 m (3,200 ft) in Prowers County to about 1800 m (6,000 ft) around Limon and near the foothills of the Rockies. Principal rivers include the South Platte, Arikaree, Big Sandy, Republican, and Arkansas. Precipitation is low, less than 50 cm (20 in) per year with most of that falling in spring and summer; total precipitation varies greatly between years at a given location and varies significantly more than in mixed grass or tallgrass systems (Wiens 1972). Mean monthly temperatures range from -12ˇC (10ˇF) in winter to 38ˇC (100ˇF) in summer. Localized severe weather is not uncommon, and blizzards, hailstorms, and tornadoes occur in most years.

The dominant habitat in this physiographic area is shortgrass prairie. Shortgrass is dominated by two low-growing warm-season grasses, blue grama and buffalo grass; western wheatgrass is also present, along with taller vegetation including widespread prickly-pear cactus and yucca, and cholla in the south. Sandsage prairie is found where sandy soils occur, and is dominated by sand sagebrush and the grasses sand bluestem and prairie sand-reed. Mixed grass (needle-and-thread, side-oats grama) and tallgrass (big bluestem, little bluestem, switchgrass) communities occur locally.

Ecological forces that shape the shortgrass prairie landscape include fire, grazing, and climate. Little is known about the ecological role of fire in shortgrass, although before the advent of fire suppression by humans, fire was probably less frequent than in either mixed grass or tallgrass prairie (Weaver et al. 1996). Prescribed burns have been used in shortgrass to remove woody vegetation, cacti, and accumulated litter and to improve grazing conditions for livestock, but the grasses recover slowly, requiring 2-3 years with normal precipitation (Wright and Bailey 1980). Before widespread settlement by European-Americans, grazing regimes consisted of native ungulates wandering widely across the shortgrass prairie--spreading over the landscape the impact of their grazing and trampling--and prairie dog colonies expanding, contracting, and moving in response to climatic influences on vegetation so that, at any given time, they grazed some areas intensively and others not at all (Knopf 1996b). The severity of the semi-arid climate and the sharp differences over relatively short distances in precipitation produced contrasts in vegetation and advanced the formation of a variegated landscape. Grassland birds thus evolved in a shifting landscape mosaic, with access to patches of vegetation in a variety of successional stages and conditions.

A second habitat in this physiographic area is lowland riparian. In the shortgrass prairie, lowland riparian habitats occur along the few stream and river courses. Riparian vegetation is dominated by plains cottonwood, willow shrubs, and introduced species such as Russian-olive and Chinese elm. Trees were uncommon features of the shortgrass prairie before European settlement (Hart and Hart 1997); development of woody vegetation has been facilitated in historical times by alteration of natural river flow regimes, a result of irrigation drawdown and reservoir construction for flood control. Animal species of eastern deciduous forests, including birds, have capitalized on the recent development of wooded corridors, and many of the species now found in this habitat in the shortgrass region are actually eastern natives (Knopf 1986). Their impact on indigenous species is largely unknown.

Additional habitats in this physiographic area that support priority bird species are shore/bank (a habitat type found along watercourses, reservoirs, and playas) and wetlands (including marshes, wet meadows, lakes, and ponds).

Conservation Issues

The driving conservation issues in the Central Shortgrass Prairie are habitat loss and habitat alteration. Colorado's rapid population growth and accompanying land development are responsible for much of the habitat conversion and degradation. Within the shortgrass area, much of that development is concentrated along the Front Range in Denver, Boulder, Jefferson, Arapahoe, Larimer, and Douglas counties, where population densities are as high as 1,180 people/kmÓ (3,050/miÓ). Human population densities in counties within the physiographic area but away from the Front Range corridor range from as high as 6.6 people/kmÓ (17.1/miÓ) in Morgan County to as low as 0.4 people/kmÓ (1.0/miÓ) in Kiowa County (U.S. Department of Commerce 1991).

Because much of the shortgrass prairie is too dry to farm without irrigation, the proportion of plowed land is not high and much of the region is still grassland (Weaver et al. 1996). In Colorado, approximately 67% of the historical shortgrass prairie still exists (Knopf 1994), although some sources suggest that only 20% of the original shortgrass prairie exists in an unaltered state--the rest having been converted to cropland and urban development or degraded by overgrazing. Conversion to agriculture results in an absolute loss of grassland habitat, but much of the area is managed for grazing, which maintains grassland habitat but often with changes in plant height, vigor, and community composition.

Ideally, modern management would replicate the timing, intensity, and landscape distribution of the natural disturbances that shaped the shortgrass prairie (unfortunately, detailed information about presettlement conditions is lacking). In practice, however, modern grazing tends to spread grazing intensity evenly, producing a comparatively homogeneous landscape. Shortgrass birds are left with few options if grazed prairie does not meet their habitat needs. "There is no shortage of grazed and hayed lands for those species that benefit from these activities. By comparison, habitat for species with breeding requirements that are not compatible with grazing and haying is exceedingly rare and continues to diminish" (Dobkin 1994).

Habitat loss and alteration have contributed to population declines among shortgrass bird species. These declines have been largely overlooked by the conservation community until recently, due at least in part to widespread concern about population declines in Neotropical migrant bird species of the eastern deciduous forest. The result of newly redirected focus is that grassland habitat is now arguably the highest conservation priority in the U.S. "As a group, grassland species have shown steeper, more consistent, and more geographically widespread declines than any other behavioral or ecological grouping of North American species," including Neotropical migrants (Knopf 1996b).

Conservation Opportunities

Colorado Bird Observatory has developed Prairie Partners, a cooperative and voluntary program to work with landowners, leaseholders, and land managers in the U.S. and Mexico to conserve shortgrass prairie and the birds that depend upon it. Participants can draw upon information gathered in a Best Management Practices manual to facilitate their contributions to bird conservation, and each participant receives a certificate of participation and an annual report detailing the overall contributions of all partners.

The USDA Natural Resources Conservation Service oversees a number of private landowner programs stemming from the1996 Farm Bill, the Federal Agriculture Improvement and Reform Act. These programs provide a number of conservation opportunities in Physiographic Area 36. They include the Environmental Quality Incentives Program (EQIP), Wetlands Reserve Program (WRP), Conservation Reserve Program (CRP), and Wildlife Habitat Incentives Program (WHIP).

Avifaunal Analysis