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Ecology and Management of Islands, Peninsulas and Structures for Nesting Waterfowl

Mississippi River: Environmental Management Program--A Test of Predator-free Nesting Islands

John F. Wetzel and Robert B. Dahlgren
(JFW)Wisconsin Department of Natural Resources, 3550 Mormon Coulee Road, and
(RBD)U.S. Fish and Wildlife Service, P.O. Box 2484--La Crosse, WI 54601

Seldom are new wildlife management techniques and theories extensively tested because of manpower, funding, land control, or other limitations. Presently, however, we have an opportunity to combine our knowledge of island nesting by mallards (Anas platyrhynchos) to improve the design of islands to be constructed under the Environmental Management Program (EMP) on the Upper Mississippi River System (UMRS). The EMP was authorized by Public Law PL-662 and includes programs for wildlife improvement, resource monitoring, and computer inventory, as well as studies of navigation and recreation. Through the Habitat Rehabilitation and Enhancement Program, or related navigation programs, nesting islands will be constructed. Supervision of the program is by the U.S. Army Corps of Engineers (COE) through coordination with the U.S Fish and Wildlife Service, state conservation agencies, and others. Plans call for approximately 50 nesting islands varying in size from 5 to 40 acres in Pools 4, 5, 7, 8, 9, 10, and 11 in the next 10 years. Two islands (Mallard and Swan) have recently been constructed by the COE in Pool 5 as the Weaver Bottoms project, and are being planted to vegetation expected to attract nesting ducks.

Mallards, wood ducks (Aix sponsa), and blue-winged teal (Anas discors) commonly nest throughout the UMRS, but mallards are the primary nesters on islands. Four islands in Pool 8 have been visited each 2 weeks from late April to mid-July by Ron Nicklaus, former employee of the Wisconsin Department of Natural Resources, from 1981 to 1987. This study is being continued in 1988 but expanded to include 4 islands in Pool 7, 5 islands in Pool 11, and 7 islands in Pool 13, with monthly visits being made from early May to the end of nesting. Most of these islands are free of mammalian predators (PF), but raccoons and foxes are present on some. Predation by birds is presumably by gulls (Larus argentatus) and crows (Corvus brachyrhynchos).

Nest densities have varied from 0 to 78 nests per acre and average 10 for all islands checked. Hatching success through 22 June for all UMRS islands highest on PF islands (78%) and much lower for islands with mammalian predators (21%) where we have lost both nests and nesting hens. Nest density is also much higher on PF islands (29 nests/acre) than on those with mammalian predators (1.7), although we are much more confident of accounting for all nests on PF islands chiefly because of the intensity of our work there. Mallards commonly seek nesting sites with canopy coverage over 75%, often in tangles of brush, roots of fallen trees, under fallen trees and vines, at the base of trees, and in various types of cavities. They do not seem to favor grassy islands more than forested islands, but our sample of grassy islands is limited. Nesting waterfowl using the UMRS are not only plagued with predation, but with flooding, marginal nesting cover, and rapid erosion of islands. Our goal for current and planned studies is to develop recommendations for the best design and management measures for future nesting-island construction.

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