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Landscape Level Determinants of the Distribution and Abundance of Black Ducks Wintering in Habitats along the Atlantic Coast

Dennis G. Jorde and Jerry R. Longcore

Abstract: More than 70 % of the continental population of black ducks winter in the Atlantic Flyway, mostly in estuarine habitats along the mid Atlantic coast where segments of the population have shifted use of habitats and the size of the Atlantic Flyway population has declined. In response to a lawsuit about the population decline of black ducks, the United States implemented restrictive hunting regulations in 1983 and Canada did so in 1984 to reduce annual harvest. The number of black ducks counted during midwinter surveys did not respond as expected, partly because regulations in Canada were ineffective until after 1986 and retrieved kill in Canada did not decline appreciably until 1990. A question has been raised, however, about the ability of existing estuarine habitat along the Atlantic coast to provide the resources (in quantity and quality) for the current population of overwintering black ducks.

To address this issue we will focus on habitat changes at the landscape level for black ducks wintering in the Atlantic Flyway. We will determine changes as feasible in quantity and quality of estuarine habitat in recent years and relate those data to historical densities of wintering black duck populations in discrete habitat units, i.e., on the basis of an entire state or subsection of a state. We will then assess the potential of current habitats to winter more black ducks than are now (last 5 years) using those habitats.

Results of this project will provide data on the status of wintering habitats used by black ducks, which can be used by federal and state wildlife management agencies to protect or restore critical habitats on a state wide basis. Perhaps data will enhance the ability to forecast population levels in concert with changes in estuarine habitat in the Atlantic Flyway in the future. Results will probably satisfy needs of the Atlantic Flyway Council regarding management of black duck populations and habitats and perhaps that of the Atlantic Habitat Joint Venture and Black Duck Joint Venture under the North American Waterfowl
Management Plan.



Hunting restrictions in the United States (1983) and Canada (1983 - 1989) have reduced the number of black ducks harvested in the Atlantic Flyway (left figure) to a level below the number of ducks counted during the Mid winter Inventory (MWI). The North American harvest of black ducks (right figure) has finally decreased to a point of intersection with the MWI indicating that continued harvest restrictions are important to increasing the continental population of black ducks. (Figures by J. Longcore).

Estuarine habitat along the coast of Maine where black ducks forage among rockweed ledges at high tide (shown) and exposed mudflats at low tide during winter (photo by D. Jorde). Estuarine bay along the coast of Maine where black ducks seek shelter and aquatic foods (Photo by D. Jorde).

Upland freshwater impoundment adjacent to the coast of Maine (Petit Manan NWR) used by black ducks during migration and for breeding (Photo by D. Jorde). Tidally influenced freshwater habitat of Merrymeeting Bay along the coast of Maine where extensive beds of wild rice attract black ducks and other waterfowl (Photo by D. Jorde).
Tidally influenced freshwater wetlands and saltmarshes along the coast of New England states are important migration and wintering areas for black ducks, but also are choice sites for housing development projects and other human encroachments (Photo taken at Rachael Carson NWR by D. Jorde). Forested estuarine habitats along the New England coast provide important food resources, shelter, and open water for black ducks during winter (Photo taken at Great Bay NWR in New Hampshire by D. Jorde). Brackish marsh at Parker River NWR, Massachusetts is important habitat for wintering black ducks (Photo by G. Baldassarre).

Forested islands along the Connecticut coast and Long Island Sound of New York attract concentrations of black ducks and other waterfowl during winter (Photo taken at Stewart B. McKinney NWR by D. Jorde). Estuarine saltmarsh habitats remaining along the mid Atlantic are an oasis to black ducks during migration and winter, and also are high density nesting sites where most of the coastal wetlands have been lost to development (Photo taken at Charles E. Wheeler State Management Area in Connecticut by D. Jorde).
Brackish marsh at Parker River NWR, Massachusetts is important habitat for wintering black ducks (Photo by G. Baldassarre). Tidal creek with Sagittaria in Delaware (Photo by B. Clark).
Intense development in tributaries of the Chesapeake Bay has greatly lessened the amount of habitat available to wintering black ducks (Photo taken along the western shore of Maryland by G. M. Haramis). Fresh estuarine bay marsh ditched for mosquito control (Photo taken at Blackwater NWR, Maryland by G. M. Haramis).

 

Saltmarsh habitats of islands in the Chesapeake Bay are among the most important breeding and wintering areas still remaining for black ducks in the Bay region (Photo taken at Martin NWR on Smith Island by D. Jorde). Coastal impoundments similar to brackish fresh estuarine marsh are important to black ducks and other waterfowl along the coast of Virginia (Photo taken at Chincoteague, Virginia by G. M. Haramis).