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
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).
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
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
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).
The shortgrass prairie bird community is comparatively depauperate, possibly as a result of the
limited vegetation structure available for nesting and foraging, or as a result of the unpredictable
and highly variable weather (Wiens 1974). In spite of the extent of prairie habitats in North
America (comprising 17% of the land area), only 10 bird species are endemic to upland grassland
areas (Knopf 1994). Other species that are present are only secondarily associated with
grasslands. As examples of this species paucity, a study on 14 sites throughout the shortgrass
region recorded only eight breeding species (Wiens 1974), and a study on the Pawnee National
Grassland recorded only 14 bird species on 112 point-count surveys (Knopf 1996b).