Food availability and waterfowl use on mid-migration habitats in central and northern Ohio
Jason D. Steckel, MS
Advisor: Robert Gates
Destruction of wetland habitat in North America throughout the late 1900s, combined with decreased precipitation levels in key breeding areas, led to a severely depressed continental waterfowl population by the mid 1980s. The North American Waterfowl Management Plan (NAWMP) was initiated to restore waterfowl populations to levels of the mid 1970s. The plan is funded in part by the North American Wetland Conservation Act (NAWCA). The NAWMP is a delivery mechanism for wetland and waterfowl conservation, and operates on a regional scale through partnerships called joint ventures. The Upper Mississippi River and Great Lakes Region Joint Venture, which includes Ohio, was one of the first joint ventures to establish a biologically based mid-migration waterfowl habitat conservation objective. The objective to conserve 216,000 ha of migration habitat, was largely based on estimates of energetic carrying capacity (ECC) and the assumption that food energy is a factor that potentially limits the survival and reproduction of migratory waterfowl. I measured availability of seeds, tubers and submerged aquatic vegetation on 28 wetlands associated with 4 managed wetland complexes in northern and central Ohio, prior to fall migration 2001 and 2002 to evaluate the joint venture estimate of ECC (1,236 duck-use-days per ha) (DUD/ha) for managed migration habitat. ECC of managed habitat, prior to autumn migration, was 7,434 DUD/ha during 2001 and 2,018 DUD/ha during 2002. Weekly diurnal and nocturnal surveys also were conducted to determine the number of birds using wetlands and the relationship of observed use to ECC. ECC values were higher (F = 10.28, P = 0.004) in 2001 on wetlands under a moist soil draw down management regime than those under a continuous water level management regime, but did not differ in 2002. Use of moist soil draw down wetlands did not differ from partial draw-down wetlands, and no significant correlation existed between ECC and observed use during autumn migration. This suggests that use of managed wetlands by migratory waterfowl during autumn is limited by some factor other than ECC, possibly disturbance. Although I observed a high degree of variability in ECC, adequate food energy was present to accommodate observed levels of use. Sampling also was conducted before spring migration 2002 to determine residual ECC prior to spring migration. Estimated residual ECC before spring migration 2002 was 83 DUD/ha for managed migration habitat. As with autumn, moist soil managed wetlands had significantly higher ECC values than did partial draw-down managed wetlands. Although food availability did not appear to limit use of wetlands during autumn migration, my study casts doubt on the ability of existing mid-migration habitat to provide sufficient food resources to satisfy energetic requirements of waterfowl populations expected under NAWMP.