Continuing an ancient ritual, the majestic canvasback duck is returning to spend another winter on the Chesapeake Bay.
The canvasback is easily recognized by its distinctive coloration and wedge-shaped head and bill profile. Male canvasbacks are off-white with reddish-brown heads, black breasts and tails, and red eyes. Females are gray-brown with brownish-tan heads.
In the Chesapeake Bay, canvasbacks form large flocks or "rafts" on the open water, often numbering in the thousands. Canvasbacks belong to a group of waterfowl known as pochards, or diving ducks. Large, webbed feet on legs located toward the rear of their bodies make them agile underwater swimmers. The location of the legs makes land travel difficult, though, and they are rarely found far from the water's edge.
Canvasbacks use their long, sloping bill to dig in the bottom sediments for food. Root stalks, tubers and stems of submerged aquatic vegetation (SAV), as well as bottom-dwelling animals, such as small crustaceans and clams, are the canvasback's preferred foods. In the Bay, with the decline of SAV, the Baltic clam has become a critical food source for wintering canvasbacks.
The largest proportion of canvasbacks nest on the North American prairies, from Minnesota and the Dakotas through Manitoba, Saskatchewan and Alberta. By mid-May, the females build a nest of cattail, bulrush or whitetop grass and lay a clutch of eight to 10 greenish eggs. Once the eggs are laid, the males move to larger lakes to molt, leaving the females to raise the young.
The ducklings hatch after about 25 days and begin to forage in the wetland for small invertebrates and plants. Poor weather, pesticide poisoning and predation by mink and raccoons are threats to eggs and ducklings.
As winter approaches, lakes and ponds freeze, and harsh weather across the prairies limits food, so canvasbacks migrate to warmer climates. During thewinter, canvasback flocks gather in Chesapeake Bay, San Francisco Bay, the Mississippi Delta region and adjacent Gulf Coast, and interior Mexico.
Historically on the Chesapeake Bay, the Susquehanna Flats, the large shoal area at the head of the Bay, attracted tens of thousands of canvasbacks because of the lush beds of their favorite food, a species of SAV known as wild celery (Valisneria americana). In fact, the scientific name for canvasbacks, Aythya valisineria, was derived from the scientific name for wild celery.
It has been estimated that during Colonial times, as many as 1 million canvasbacks may have wintered on the Chesapeake. In the 19th century, their seemingly endless abundance and excellent eating quality made the canvasback a good winter food source and a favored dish in many restaurants along the East Coast. Because of their tendency to aggregate in large groups on the open water, canvasbacks were vulnerable to overharvesting. By the end of the 19th century, commercial hunters were using large-bore shotguns and batteries of cannon and punt guns to assault rafts of canvasbacks, killing dozens of birds with one shot.
The birds were shipped in canvas bags by boxcar to markets from Baltimore to Boston. Concern grew over this unregulated harvest until commercial hunting ended with the passage of the Migratory Bird Treaty Act of 1918, which empowered the federal government to set seasons and bag limits on the hunting of migratory game birds.
In the 1950s, the 250,000 canvasbacks that wintered on the Chesapeake represented one-half of the entire North American winter population. By the early 1980s, only about 50,000 canvasbacks were wintering on the Bay.
Of the many factors responsible for declining canvasback populations, habitat degradation (wintering, migratory and summer nesting grounds) has had the largest impact. The decline of water quality in the Chesapeake greatly reduced the amount of SAV, especially the canvasbacks' favorite food, wild celery tubers. Canvasbacks have had to change to a poorer winter diet of mainly Baltic clams, which may affect winter survival rates.
Other problems canvasbacks may encounter on the Bay include toxins entering their food supply, disturbance from shoreline development and recreational activities, oil spills, disease and the illegal hunting of females by hunters who misidentify canvasbacks as female mallards.
However, wintering canvasbacks have again increased on Chesapeake Bay. This trend is illustrated by three-year average midwinter counts of canvasbacks on Chesapeake Bay. Between 1986 and 1988, an average of more than 49,000 canvasbacks were counted. Between 1995 and 1997, the average number of wintering canvasbacks exceeded 64,000! This figure also exceeds the Year 2000 goal of 62,000 wintering canvasbacks set forth in the Chesapeake Bay Waterfowl Policy and Management Plan.
Like all migratory birds, canvasbacks need dependable and high-quality habitat for breeding, migrating and wintering. The prairie wetlands (or "potholes") of North America are vital to the reproduction of many species of waterfowl, including canvasbacks.
Recently, favorable weather conditions and programs to restore wetlands have increased wetlands and boosted many duck populations. Record numbers of ponds have led to record numbers of both redheads and canvasbacks in the prairie potholes region.
Although canvasback numbers appear to be increasing, there is much that can be done to maintain this favorable trend. Improving water quality promotes the regeneration of SAV, an important source of food for canvasbacks and other waterfowl.
Other beneficial actions include setting proper harvest limits, establishing open water sanctuaries and continuing research regarding habitat use and food resources. These actions, combined with the protection of nesting areas in the North American prairies, are vital to the survival of these magnificent waterfowl and will ensure that great rafts of canvasbacks continue to grace Chesapeake winters.