The midwinter survey of black ducks, locally and regionally

The Midwinter Waterfowl Inventory (MWI) has been conducted consistently in Maryland since 1955 and in Virginia since 1957. Maryland currently focuses surveys in 30 segments along the Chesapeake Bay, Potomac River, and Atlantic Coast, whereas Virginia focuses on 22 segments centered over the eastern shore of Chesapeake Bay and along the tidewater areas of Back Bay and western shore tributaries. Until 1980, the survey along the Potomac River was shared and sometimes duplicated by Maryland and Virginia but now is flown entirely by Maryland. The MWI number of black ducks wintering in Maryland shows a decreasing trend until 1983 when the trend reversed, possibly in response to restrictive hunting regulations. In Virginia, the MWI index of black ducks reached its lowest point in 1965 at just under 4,000 ducks, steadily increased to a peak of 18,000 black ducks in 1981, then began a steady decline to the present. The number of black ducks on the Potomac River reached a low of 400 ducks in 1971, 1984, and 1985 but generally attracts 500-1,500 ducks each year. The distribution of black ducks in the Bay has also changed from upper Bay areas to mid-Bay eastern shore sites and the Potomac River. Whereas the decline in black ducks seems to be related to hunting, the redistribution of black ducks in Maryland seems to be associated with habitat changes in water quality and the decline of submerged aquatic vegetation.