Increasing loss of habitat threatens elusive black duck
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On a treeless island in the middle of the Chesapeake Bay, several biologists are searching for an elusive quarry. Trudging through mud and marsh grass, it appears that, besides the biting flies, there is little else present.
Suddenly, not more than a few feet away, a bird bolts straight up from the marsh into the air. It is the elusive black duck. Not black at all, its plumage is predominately a dark, mottled brown. The sooty color makes this duck appear black against the sky. Hens and drakes are almost identical in appearance, with the males being slightly darker. Black ducks are closely related to mallards and are often mistaken for females of that species.
The black duck is one of North America’s wariest waterfowl, and few surpass it in prestige among hunters throughout the Mississippi and Atlantic Flyways.
Primarily a species of eastern North America, the black duck is found east of the Great Plains and south of the tundra. Black ducks migrate through the Chesapeake Bay region, as well as overwinter and breed here.
They use a variety of habitats and feed on a variety of plants and animals. Black ducks eat invertebrates and seeds in bottomland hardwoods. In marshes, their food includes invertebrates, fish, emergent wetland plants and submerged aquatic vegetation (SAV).
Small islands and isolated marshes that are relatively safe from predators and human disturbance are the last stronghold for black ducks nesting in Chesapeake Bay. Only a few, small, nesting islands remain.
Unlike human-tolerant mallards that nest on lawns, docks or even docked boats, black ducks remain a wary bird. The nest is a hollowed-out place on the ground or a stump lined with grass and down. An egg is laid daily until the clutch, which usually consists of about nine buff green eggs, is complete.
Black ducks are monogamous and form a pair bond that lasts until about 14 days after incubation starts. After this time, the hen is on her own to complete the incubation and raise the young. Hens will often feign an injury if the nest is threatened, and will try to lure the intruder away from the nest. The eggs hatch in about 26 days.
The ducklings are precocial, meaning that they are born with down and their eyes are open. The ducklings are also mobile, following the hen to find their own food. Ducklings show their first flight feathers at about 3 weeks and can fly by the time they are 2 months old.
Severe droughts of the 1930s and the agricultural drainage of prairie pothole regions of the Dakotas and nearby Canadian provinces drastically reduced the black duck population and permanently altered the nesting grounds for most North American ducks. During that same period in the East, black ducks remained relatively secure in the coastal marshes, rivers and wooded wetlands of the Northeast and Canada.
Since 1955, though, annual midwinter waterfowl surveys have revealed a continuous decline in black duck numbers. Between 1956 and 1958, an average of 111,000 black ducks were found in the Chesapeake Bay watershed. Between 1996 and 1998, that number dropped to an average of 24,000.
There are many reasons for the decline of the black duck, including overhunting, loss and deterioration of habitat, years of pesticide use on breeding and wintering grounds, and competition and crossbreeding with the closely related mallard.
In 1983, state, federal and Canadian waterfowl managers agreed that hunting restrictions were necessary to halt the decline. Shorter hunting seasons and a reduction in bag limits were adopted. Although these restrictions helped to stabilize the North American black duck population, loss of habitat remains a threat.
Habitat lost to erosion and development is a continuing concern in the decline of breeding populations in the Chesapeake Bay. A significant amount of shoreline nesting areas has been eliminated by housing developments, shoreline erosion controls, and the filling and draining of wetlands. Sturdy, offshore hunting blinds, where black ducks used to nest, are much less prevalent.
Meanwhile, sea level rise and erosion are continuing to claim the remaining islands that black ducks favor for nesting in the Chesapeake Bay.
Black ducks also need good brood-rearing areas, such as SAV beds and wetlands, that are close to the nest. Brood-rearing areas must be isolated and free of predators. Black ducks that must move their broods great distances over land or water risk losing their chicks to predators.
Resident mallards may also adversely affect black ducks. In Maryland, farm-reared mallards were released for recreational hunting. These mallards began to breed. Nesting preferences are similar for both the mallard and the black duck, although much of the resident mallard population is semi-domesticated and will nest close to humans. Increasing resident mallards may compete with black ducks for nest sites and food sources.
To reverse declining waterfowl populations, wildlife managers and biologists are using a variety of techniques to protect and restore vital habitat. Aerial surveys of waterfowl have identified areas of the Chesapeake Bay that are important for the various waterfowl species, including black ducks. With this data, managers can target areas that may require greater protection. Dredge material is being used to rebuild severely eroded islands, which are valuable for black duck nesting.
Researchers are also trying to determine the effects that mallards may have on black ducks in terms of competition for food and habitat and interbreeding between these two species.
Historically, large numbers of migrating black ducks arrived on the Bay in late fall. They spent winters feeding on the extensive SAV beds in the shallow bays of the upper Eastern Shore and on the abundant seeds and invertebrates in the marshes and at the heads of tidal creeks and rivers. The black duck was once widely distributed over Chesapeake Bay’s many tributaries.
Today, black ducks concentrate in and are dependent upon the dwindling undisturbed wetlands of the Chesapeake Bay.
- Category: Wildlife + Habitat
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