WSP03031

• File Number: 8543
• Description: Closed Basin Division
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 6/1/1981
• Title: Fish and Wildlife Plan - Closed Basin Division - San Luis Valley Project
• Water Supply Pro - Doc Type: Report/Study

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A. Waterfowl Production

Several factors are critical to duck production: (1) availability and quantity
of water for breeding pairs, (2) availability of water to sustain brood
survival, and (3) quantity and quality of nesting cover. In the San Luis Valley,
factors (1) and (2) operate to limit duck production. Availability and quan-
tity of water has been well documented as necessary for attracting breeding
pairs. There is a very high correlation between the number of water areas
available during spring migration and local breeding populations (Stewart and
Kantrud 1974, Schroeder et al. 1976).

Although numbers of ponds, regardless of permanency, are important in attracting
breeding pairs, availability of midseason water areas and juxtaposition of
those areas are critical to brood survival. Areas with temporary and seasonal
wetlands that attract breeding pairs but do not have midseason water for
brooding act as death traps. Within the Closed Basin project area, drain
ditches serve as extremely important brood areas. In recent years, changing
irrigation methods have reduced available midseason water and breeding pair
habitat resulting in decreased duck production. However, the San Luis Valley
is still the most important waterfowl production area in Colorado and probably
the southermost significant mallard production area in the United States
(Hopper et a1. 1975).

Hopper et al. (1975) found an average of 56,000 breeding ducks utilizing
231,000 acres of wetlands in the San Luis Valley from 1965-1971. Assuming
(1) 28,000 breeding pairs, (2) 50-percent nesting success (Schroeder 1972), and
(3) 6 fledgling (Class llc-lll) per brood (Anderson 1967, Pospahala 1969,
Schroeder 1972, Robinson 1971), the San Luis Valley wetlands produced
84,000 ducks in an average year. Annual production varied from 69,000 to
99,000 birds depending on available habitat and flyway population levels.

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Hopper et al. (1975) identified five major breeding concentration areas which
accounted for 20 percent of breeding waterfowl populations'in the San Luis Valley
but represented only 3 percent of the survey area. Two high density areas,
Mishak Lakes and San Luis/Head Lakes, are either within or adjacent to the
Closed Basin project area and produce an average of 1,704 ducks annually at a
density of .59 and .42 ducks per wetland acre, respectively. Low concentration
areas of the valley produce an average of 67,206 ducks annually at a density of
.31 ducks per wetland area.

The BLM managed Blanca Wildlife Habitat Area (WHA) has been developed and inten-
sively managed for waterfowl production. Substantial warm-and cold-water
fisheries have also been developed. Artesian waters are used to maintain
established ponds, wetlands, and wetland habitat. Recent surveys by BLM indi-
cate that waterfowl production averages about 2.0 ducks per acre of wetland per
season and about 0.5 ducks per acre of terrestrial vegetation per season.
Fishery surveys have indicated an average annual cold-water production rate of
about 175 pounds per acre.

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