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<br />UU,L....,v <br /> <br />.--.~, ',."....,.--.' ~'., <br /> <br />. <br /> <br />. ,> <br /> <br />I <br />I <br />I <br /> <br />-I <br />i <br />I <br /> <br />The description of the existing conditions within the Closed Basin Division <br />and the San Luis Valley is separated into (1) waterfowl production, (2) other <br />water bird use, and (3) bird species of high Federal interest. <br /> <br />. (1) Waterfowl Production - Several factors are critical <br />to duck production: (1) availability and quantity of water for breeding pairs, <br />(2) availability of water to sustain brood survival, and (3) quantity and <br />quality of nesting cover. In the San Luis Valley, factors (1) and (2) operate <br />to limit duck production. Availability and quantity of water has been well <br />documented as necessary for attracting breeding pairs. There is a very high <br />correlation between the number of water areas available during spring migration <br />and local breeding populations (Stewart and Kantrud, 1974, Schroeder et. al. 1976.) <br /> <br />Although numbers of ponds, regardless of permanency, are important in attracting <br />breeding pairs, availability of mid-season water areas and juxtaposition of those <br />areas are critical to brood survival. Areas with temporary and seasonal wetlands <br />that attract breeding pairs but do not have mid-season water for brooding act as <br />death traps. Within the Closed Basin project area, drain ditches serve as extremely <br />important brood areas. In recent years, changing irrigation methods have reduced <br />available mid-season water and breeding pair habitat resulting in decreased duck <br />production. However, the San Luis Valley is still the most important waterfowl <br />production area in Colorado and probably the southernmost significant mallard <br />production area in the United States (Hopper et. al. 1975.) <br /> <br />Hopper et. al. (1975) found an average of 56,000 breeding ducks utilizing 231,000 <br />acres of wetlands in the San Luis Valley from 1965-1971. Assuming (1) 28,000 <br />breeding pairs (2) 50 percent nesting success (Schroeder 1972), and (3) six <br />fledgling (Class llc-lll) per brood (Anderson 1967, Pospahala 1969, Schroeder <br />1972, Robinson 1971), the San Luis Valley wetlands produced 84,000 ducks in an <br />average year. Annual production varied from 69,000 to 99,000 birds depending <br />on available habitat and flyway population levels. <br /> <br />:-1 <br />-] <br />J <br />I <br />1,[ <br />J <br /> <br />-- <br /> <br />" <br />Hopper et. al. (1975) identified five major breeding concentration areas which <br />accounted for 20 percent of breeding waterfowl populations in the San Luis <br />Valley but represented only three percent of the survey area. Two high density <br />areas, Mishak Lakes and San Luis/Head Lakes, are either within or adjacent to the <br />Closed Basin project area and produce an average of 1,704 ducks annually at a <br />density of .59 and .42 ducks per wetland acre, respectively. Low concentration <br />areas (218,000 acres of wetlands) of the valley produce an average of 67,206 ducks <br />annually at a density of .31 ducks per wetland area. Table 1 provides a break- <br />down of duck production in various locations in the Valley during the period of <br />1964-78. <br /> <br />7 <br />