Low water levels during critical phases of the breeding cycle appear to have caused population declines of waterfowl and other marsh birds on the Spring Run Game Management Area. Pair-counts indicated a decline from 70 pairs of waterfowl in 1965 to 2 pairs in 1968. Nest success of upland nesting blue-winged teal (Anas discors) averaged 33% and mallards (Anas platyrhyncos) averaged 23%. Blue-winged teal selected nest sites closer to water than did mallards (314 feet versus 424 feet). Teal nested in ungrazed bluegrass (Poa pratensis) in preference to alfalfa (Medicago sativa) hayland. Bromegrass (Bromus inermis) was readily used by teal and mallards when it became available for nesting. Nest success of species nesting overwater was considerably higher: Redheads (Aythya americana) were 55% successful and 93% of 75 coot (Fulica americana) nests hatched. A study of dummy-nests showed nest success significantly higher on ungrazed than on grazed bluegrass. Grazing did not significantly lower total mouse populations but did change species composition because deer mice (Peromyscus maniculatus) increased as other species declined with grazing.
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Waterfowl in relation to land use and water levels on the Spring Run Area