Winter Waterfowl

Background
A diversity of ducks (both divers and surface feeding dabblers), geese, and swans collectively comprise the “waterfowl” that use our coastal systems during the late fall-winter migration season. When cold temperatures cause freshwater areas to freeze, our embayments become an important food resource to local birds that disperse short distances, and longer distance migrants from regions north and west. With wetlands long under siege from human encroachment, waterfowl populations became a valuable index of wetland ecological health and biodiversity value, as most wildlife populations and communities slowly became captive to an expanding human footprint.

American Black Ducks  
American Black Ducks (Anas rubripes) are a dabbler with a robust migrant population that’s highly dependent on estuaries in winter, that’s managed as a game (hunted) species, and which historically bred extensively in Massachusetts.  Black Ducks suffered declines due to wetland loss and competition with Mallards (Anas playrhynchos) which adapted better to human use. For these reasons black ducks are a good target species for research and conservation. Allens Pond estuary had been studied extensively by the Lloyd Center due to its high abundance and diversity of waterbirds. Starting in December of 1988, the Center began focusing on the importance of the system specifically to black ducks in winter. This effort evolved into a regional assessment of all waterfowl utilizing systems from the Sakonnet River in Rhode Island to Apponagansett Bay in Dartmouth (Figure 1), and the “Annual Winter Waterfowl Count” was born.

The Annual Winter Waterfowl Survey
This survey provides an assessment of the abundance and habitat use of a variety of species from the American Black Duck and common Bufflehead (Bucephala albeola) diving duck, to occasional rarities. The familiar Canada Goose (Branta canadensis) also adapted to human use and includes both resident and migrant populations, so Canada Geese trends also became an important species to survey during the count.

An early December (early meteorological winter) and late January or early February (late meteorological winter) survey are conducted, the two Sunday surveys accounting for differences in both migration schedules and response to weather trends, mainly cold causing ice coverage in freshwater.  Volunteers and Lloyd Center staff identify and count all individuals present at their sites to the furthest extent of tidal influence, which generally is the edge of the salt marshes, and estimate percent ice coverage. Ice is an important parameter at coastal sites as it determines the amount of open water available for foraging, and greatly impacts use of some systems. In addition to temperature trends, other environmental factors that may influence survey outcomes include tide level, wind conditions, storm events just prior to the count, and the amount of snow cover in nearby fields where some species may feed.

Long-term trends – A 35 year snapshot
As part of this effort, Lloyd Center staff has been compiling 35-years’ worth of data. Table 1 shows size and ice coverage for sites with free flowing estuaries, unrestricted salt marshes, human made restrictions, intermittent tidal flooding, and freshwater ponds, with most ice occurring in January in ponded areas. Table 2 shows abundance of the 40 species (including hybrids and domestics) divided between swans (3), geese (6), dabblers (13) and divers (18). Table 3 depicts dominance trends overall and seasonally where Canada Goose, American Black Duck, Bufflehead, Mallard, and Red-breasted Merganser (Mergus serrator) were dominant overall and for December. A similar dominance trend occurred in January, with scaup species replacing Red-breasted merganser. Mute Swan (Cygnus olor) and Hooded Merganser (Lophodytes cucullatus) were subdominant species overall and in both December and January/February.