Land Bird Conservation Plan Colorado  

Executive Summary
Overview of Colorado
Physiographic Region 36

  • Grasslands
  • Lowland Riparian
  • Shore/Bank
  • Wetlands
  • Physiographic Region 62
    Physiographic Region 87
    Implementation Strategies
    Literature Cited
    Appendices

    Physiographic Region 36: Central Shortgrass Prairie

    Wetlands

    Description and Ecology: The habitat category of wetlands encompasses a large variety of ecosystems of large and small proportions. The state of Colorado has numerous representatives of this variety: marshes, wet meadows, seeps, springs, rivers, lakes, ponds, swamps, fens, bogs, hanging gardens, and playas (Windell et a l. 1986, Benedict 1991). Many of Colorado's wetlands, including some that support priority species, are artificial. Such wetlands include irrigated meadows and man-made reservoirs, lakes, and ponds with their associated marshes. Less than 3% of the surface area of Colorado originally occurred as wetlands (Dahl 1990). Approximately 40% to 60% (0.4-1.2 million ha; 1-3 million ac) of the original wetlands area has been lost (Dahl 1990, Wilen 1995). Losses are greater proportionately in wetlands than in other habitat types in Colorado.

    Wetlands in Colorado range in size from a few square meters (e.g., springs and splash pools) to large areas of wet meadows and riparian wet forests. They also include wetlands along riparian corridors that may continue for many kilometers, yet are quite narrow. (Discussion of riparian habitats will be found in the appropriate section: lowland riparian or high elevation riparian habitats.) What all wetlands have in common is water. The water occurs in sufficient quantities and in such patterns that the soils, geomorphology, and vegetation respond characteristically, forming repeated patterns on the landscape. The repeated patterns are categorized as types of wetlands.

    All wetlands likely play a role in the lives of birds, at least as sources of water. But many wetland types are very small and unlikely to make a large contribution to Colorado's avifauna. (Although any wetlands may be important to local conservation.) Wetlands that support high priority bird species include lakes, ponds, reservoirs, wet meadows, playas, and marshes. The remaining, smaller wetlands are perhaps best considered as patch types and important habitat components within a larger habitat matrix.

    Importance and Conservation Status: Thirty-seven of Colorado's breeding bird species are dependent on wetlands. That means that 14% of the breeding species depend on less than 3% of the state's area. Many of the species are common and are presently of little current conservation concern (e.g., Red-winged Blackbird). However two species are in need of special conservation attention in Colorado: Northern Harrier and Short-eared Owl.

    In the water-restricted western United States, water resources are necessary for life, and control of water has become a most lucrative asset. Water law in Colorado, as in most western states, recognizes water as one of a bundle of property rights. As such, water is owned, bought and sold, as property. For mining operations, agricultural irrigation, and drinking water for a growing population, water has been harnessed, moved, stored, slowed, and spread. Wetlands have often been considered impediments to efficient water use, slowing its downstream progress to areas of human use. Many wetlands have been drained and others heavily altered. Dahl (1990) estimated wetland losses in Colorado to be approximately 50%. More specific estimates for wetland losses in the Central Shortgrass Prairie are not available, and interpretations are very complicated because of the large number of created wetlands.

    Many wetland manipulations resulted in the addition of many acres of wetlands (Kingery 1998). For example, large irrigation canals move water from mountain rivers or streams into the prairie. Some of the water escapes the confines of ditches and leaks into the surrounding landscape; this escaped water often creates artificial springs. Vegetation changes around such seepages create wetlands such as wet prairie, wet meadows, small standing waters, shrub thickets, and woody groves. Such areas are often rich with birds, and where trees and shrubs occur, the associated birds may represent those found in riparian habitats.

    The largest changes in the wetlands of Colorado's prairies came from the creation of water storage facilities, reservoirs and ponds (Kingery 1998). These reservoirs are often placed on top of existing wetlands where they may greatly expand the total wetland acres. (This does not imply good or bad since there may be a significant change in wetlands or habitat type with the creation of these wetlands. It is important to remember that different wetland types are not equivalent in biodiversity terms.) The extensive patchwork of reservoirs in the Denver metropolitan area--from Fort Collins to Pueblo-- has greatly changed the regional avifauna. Birds that were undoubtedly rare or absent prior to European advancement are now common (e.g., some gulls, many waterfowl, and some wading birds). Outside of the metropolitan area, large reservoirs such as Jackson Reservoir, Bonny Reservoir, John Martin Reservoir, Neenoshe Reservoir, and many others have created large areas of wetlands, open water, shore/bank, and riparian habitats that are novel in the physiographic area.

    The wetlands that support high priority bird species in Colorado have shown variable changes over the past 150 years. Shallow lakes and ponds that supported large populations of breeding waterfowl have declined in many areas. Instead, reservoirs are often maintained with little vegetation. A common goal of water users is to provide the smallest surface area of water to limit evaporation losses; this goal often creates wetlands habitats that are relatively sterile.

    It is difficult to assess the status of marshes since agricultural practices have created numerous marshes. However, it is clear that native graminoid-dominated marshes have clearly suffered extensive losses, even more when the condition of the landscape in which they occur is considered (J. Sanderson, personal communication). For example, a marsh may have adequate breeding habitat for Northern Harriers, but a landscape that is inadequate or ecologically dysfunctional.

    Playas deserve special mention. Playas are variably sized depressions in the prairie that are usually dry. However, during wet periods, especially after heavy thunderstorms, these depressions are often filled with water and teeming with birds. In much of the physiographic area, 1998 and 1999 were wet years, and the playas provided nesting, feeding, or resting grounds for an abundance of waterfowl, wading birds, and shorebirds. The playas vary in size from hundreds of square feet to several square miles.

    The unpredictability of playas as a wetlands resource may be one factor that has led to a lack of attention from Colorado's conservation community; some playas have been filled for many years (e.g., in Huerfano County near the Spanish Peaks), but most have been filled only 2-3 years in a decade. Livestock producers often try to increase the capacity of playas in an attempt to maintain surface water for longer periods, and wildlife managers have long sought means of increasing the time that water is available in larger and deeper playas; however, other playas have been lost in the conversion of prairie to croplands. In the wettest years, these playas are visible as ponds within a sea of crops (C. A. Pague, The Nature Conservancy, personal observation).

    Current threats to wetlands include water diversions, draining, manipulation, intensive use by livestock, conversion to cropland, and conversion to residential uses in the metropolitan area (Windell 1986). Threats include direct losses--conversion of wetland types--and contextual changes. Interestingly, the pressure to provide water to urban populations has stimulated the acquisition of water rights by municipalities from large areas of the plains (e.g., Rocky Ford Ditch 1999). Such acquisitions have resulted in large areas of prairie having their local hydrology returned to a more natural state.

    The concept of no net loss of wetlands appears to be adequate for protecting the associated birds in Colorado. However, existing guidelines for wetlands mitigation, i.e., the focus on jurisdictional wetlands, rarely give adequate attention to bird communities or high priority species that are not given legal status. Cumulative changes of wetland types and loss of ecosystem-level biological attributes continue to reduce the amounts of wetlands habitats that are suitable for the more sensitive wetlands species. Recommendations for making wetlands mitigation more suitable for birds are laudable but may not adequately address the concerns for the most sensitive species.

    In summary, wetlands habitats are diverse and widespread in Colorado's Central Shortgrass Prairie. The wetland types that support most wetlands bird species are playas, marshes, wet meadows, lakes, and ponds. The status of these wetland communities is checkered, with an increase in lakes, ponds, and seeps. Losses of springs, wet meadows, and playas are notable. Marshes have probably declined somewhat, but mostly have changed from native condition to altered and scattered patches.

    Priority Species Accounts: Two species are identified as high priority for wetland habitats in Physiographic Area 36: Northern Harrier and Short-eared Owl.


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