Changes in the Wetland Habitats and Population of Breeding Black Ducks in South Central Maine
- Diffenbachi, Duane R.
University of Maine Graduate School
Thesis objectives were to: (1) determine the change between 1977-80 and 1986-87 in the wetland habitats on 151 km2 in south-central Maine; (2) determine the change between1978-80 and 1986-87 in the population of breeding American black ducks (Anas rubripes) , and other waterfowl species, on the study area; and (3) identify the characteristics of wetland habitats selected by black ducks during the breeding season.
The number of wetlands on the study area increased from a mean of 119 (range 116-123 wetlands) during 1977-90 to 128 during 1986-87, but the area of surface water decreased 43 ha (22.2%). The area of wetland types preferred by black ducks declined (deciduous forested wetlands) or remained unchanged (deciduous scrub-shrub and emergent wetlands). The total area of open water, flooded alder (Alnus ruqosa) and willow (Salix spp.), and flooded timber declined (44.4%, 65.3%, and 62.0%, respectively). The total area of aquatic vegetation increased (86.7%), and herbaceous and ericaceous vegetation that was flooded remained unchanged (+0.3% and +r4.s%, respectively). The changes in the vegetation and wetland types on the study area represented a decline in the quantity and quality of wetland habitats for waterfowl. The cause of this decline was a 3g% decrease in the number of wetlands with beaver (Castor canadensis) between 1977-80 and 1986-87.
Despite the decline in the quantity and quality of wetland habitats, the number of pairs of black ducks, mallards (Anas platyrhynchos ), hooded mergansers (Lophodytes cucullatus) , and Canada geese (Branta canadensis) increased on the study area. The number of wood duck (Aix sponsa) pairs remained the same, and common mergansers (Mergus merganser) occurred infrequently on the study area. Black ducks may have increased because of restrictive harvest regulations, mallards may have increased on the study area partly because of the availability of their preferred habitat, man-made impoundments, and Canada geese increased as a result of a successful introduction program conducted by the Maine Department of Inland Fisheries and wildlife (MDIFW). Wood ducks and hooded mergansers have been the focus of a waterfowl nest-box program conducted by the MDIFWand may have responded to those efforts; however, the number of wood ducks seemed to fluctuate on the study area. use of a wetland during the breeding season by black ducks was best predicted by the following variables: perimeter of the surface water area (SWPER, in meters), area of flooded timber (SWTIMBER, in square meters), presence or absence of beaver activity (BEAVER; I or 0, respectively)' and whether a dwelling was visible from the wetland (DWLVIS; 1 or 0, respectively.)
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