The Southern Great Plains conservation region (Region 17*) encompasses a large area extending from southeastern Wyoming and west-central Nebraska, south through eastern Colorado and west-central Kansas and Oklahoma, to eastern New Mexico and west-central Texas. Most of the region once consisted of semi-arid prairie interrupted by riparian corridors along major rivers (e.g., Platte River), with interspersed, continentally significant wetland complexes including the Rainwater Basin, Cheyenne Bottoms, McPherson Valley Wetlands, Hackberry Flat, isolated saline wetland complexes, and playa lakes. Collectively these wetlands are core of the Central Flyway migration corridor. The majority of wetlands in this conservation region are in private ownership, notable exceptions being Valentine NWR, NE (USFWS) Cheyenne Bottoms, KS (KDWP and USFWS) Hackberry Flat, OK (ODWC), and parts of the McPherson Valley Wetlands, KS (KDWP).
As with many other regions, wetland drainage and/or alteration of wetland hydrology have been substantial, with most drainage or alterations attributable to agricultural practices. For example, 91% of the original wetlands in the Rainwater Basin have been drained and converted to agricultural production (Tiner 1984). Approximately 70% of 589 playas >4 ha (or 33% of all playas) have been modified via construction of pits to concentrate runoff for use in irrigation of crops (Guthery and Bryant 1982). While these playas are not lost, their hydrology is altered in a manner that reduces their value to ducks via reducing the area available for growth of emergent vegetation and as foraging habitat (Gray 1986). This may be an important factor in that much of the food resource for migrating and wintering waterfowl is agricultural crop residue. Agricultural grains must be supplemented by natural foods so that birds are able to obtain the full range of nutrients for annual cycle events that occur in winter, particularly molt. Many remaining wetlands in this region have been altered, some positively and others negatively, by grazing and farming practices, siltation, and other factors (Guthery et al. 1982, Guthery and Stormer 1984).
An underlying conservation issue that affects wetlands and may have potentially serious implications for waterfowl in the SGP is allocation and use of water. Surface and ground water are used for irrigation to produce cereal grain, particularly corn (Bolen et al. 1989, Guthery et al. 1984). Waste grain provides an important source of energy for migrating and wintering waterfowl in the SGP, and probably has increased the carrying capacity (as determined by available food) of this conservation region (Baldassarre and Bolen 1984, Baldassarre et al. 1983).
Extensive use of water for irrigation has had contrasting effects on waterfowl populations. On one hand, much of the corn could not be grown in this region were it not for irrigation, and irrigation tail water can create favorable conditions for moist soil plant production in playa basins (Bolen and Guthery 1982, Guthery et al. 1982). Hence, irrigation can and probably has increased available food resources. Alternatively, many wetland basins have been drained or extensively altered by agricultural practices or to store irrigation water. The net effect likely has been an increase in agricultural foods (waste grain) and a decrease in available wetlands and associated moist soil habitat. Loss and degradation of natural wetlands may have reduced the amount of natural foods (moist soil plants, invertebrates) wherein birds cannot easily acquire essential nutrients that are not available in agricultural grains (Baldassarre and Bolen 1984).
Further, reduced number and area of wetlands may concentrate birds, making them susceptible to disease outbreaks, particularly avian cholera (Bolen et al. 1989, Friend 1987). In many years playas and wetlands in the Rainwater Basin are dry or greatly reduced in area and number by dry conditions. This further concentrates birds and increases the risk of mortality related to disease (Bolen et al. 1989, Friend 1987).
*Region 17 - NABCI Bird Conservation Regions 18 (Shortgrass Prairie) & 19 (Central Mixed Grass Prairie)