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<br />o <br />(..') <br />,-1 <br />....., <br />,;:) <br />("' <br />~ ... <br /> <br />probably the southernmost significant mallard production area in the <br />United States (Hopper et al. 1975). <br /> <br />Hopper et al. (1975) found an average of 56,000 breeding ducks utilizing <br />231,000 acres of wetlands in the San Luis Valley from 1965-1971. Assuming (1) <br />28,000 breeding pairs, (2) 50-percent nesting success (Schroeder 1972), and <br />(3) 6 fledgling (Class llc-lll) per brood (Anderson 1967, Paspahala 1969, <br />Schroeder 1972, Robinson 1971), the San Luis Valley wetlands produced <br />84,000 ducks in an average year. Annual production varied from 69,000 to <br />99,000 birds depending on available habitat and flyway population levels. <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 Valley <br />but represented only 3 percent of the survey area. Two high density areas, <br />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 of the valley produce an average of 67,206 ducks annually at a density of <br />.31 ducks per wetland area. <br /> <br />The National Wetland Inventory (1979) revealed 43,122 acres of wetlands in the <br />Closed Basin project area. As shown in table 1, the project area produces <br />approximately 13,620 ducks annually at a density of .31 ducks/wetland acre. <br /> <br />A resident population of Canada geese breed in the San Luis Valley. Approximately <br />100 of those utilize the Closed Basin project area for nesting and produce 160 <br />young (80 percent success, 4 yg./brood). <br /> <br />B. Other Bird Use <br /> <br />Other water bird data is very limited for the project area. Water and Power <br />conducted aerial surveys within the area to determine the general seasonal use <br />by wetland type. However, the collected data is not sufficient to extrapolate <br />production estimates. Use-day information for Alamosa and Monte Vista National <br />Wildlife Refuge (NWR) may be more appropriate in determining other water bird <br />use of the project area. <br /> <br />In general, the species have been classed into three types: raptors, <br />shorebirds, and marsh and water birds. Use by these species in the San Luis <br />Valley varies with each individual species. Some of the species such as <br />American avocets, Wilson's phalarope, killdeer, common snipe, rails, black- <br />crowned night herons, snowy egret, marsh hawk, Swainson's hawk, and short-eared <br />and great horned owls breed in the valley. The majority of the other species <br />are either fall and spring migrants or winter visitors. Most of the breeding <br />species either leave during winter months or remain in reduced numbers. <br /> <br />The Quality and quantity of the wetlands in the San Luis Valley probably have the <br />greatest effect on the breeding species that breed there. Wetland vigor and <br /> <br />2 <br />