Based on results from Long Island, black ducks eat and sleep the winter away and spend little time doing much else. During the Long Island study, hens fed mostly on mudflats and in salt marshes, but they slept and loafed in freshwater and brackish habitat. Not surprisingly, the highest numbers of invertebrates were found in mudflats and salt marshes. In a similar study at the Meadowlands in New Jersey, salt marshes that were tidally influenced and had native vegetation (spartina) produced more invertebrates than tidally-restricted salt marshes or wetland habitat that was dominated by invasive phragmites. In both cases, feeding habits were timed with the tides except during hunting season, when the birds spent most of the day hiding in protected areas and not feeding until after dark.
When favored feeding habitats freeze during the winter, black ducks and other species of migratory birds face an interesting dilemma: Should they stay or should they go? Some hens do not make very good decisions, as they remain in frozen areas and starve to death during severe weather events. During the first year of the study, a hard freeze hit Long Island. Some hens flew farther south to the Chesapeake Bay area, but some remained and moved into freshwater habitats in an attempt to weather the storm. Unfortunately, several hens did not survive. Poor body condition caused by insufficient winter food resources may account for why hens remain and are unable to survive freeze events.
During severe winters, managed impoundments and grid-ditched marsh systems freeze quickly, leaving few areas where black ducks can feed. The last study sites to freeze were restored salt marshes with adequate tidal flow. These habitats were restored by plugging old drainage ditches and through integrated marsh management or open-water marsh management. Black ducks are notoriously shy and tend to stay away from overly developed or disturbed areas. Many areas preferred by black ducks tracked during the study were relatively undeveloped watersheds with parks, state conservation lands, or refuges. Because of the birds’ behavior and feeding habits, and their need to maintain fat reserves, an ideal management approach would be to provide freshwater resting sites near restored salt marshes with tidal influence and mud flats that experience little disturbance.
Additional study sites in Virginia and New Jersey offer the opportunity to examine how food resources, habitat use, and behavior change throughout the flyway. To meet the needs of wintering black ducks, it will likely be critical to provide undisturbed, food-rich habitat at a flyway-wide scale. This would allow black ducks to move out of one area and into another when severe weather hits or disturbance is too great, while still supplying the food resources the birds need to survive and prepare for spring migration and egg laying.
Dr. Tina Yerkes is director of conservation planning at DU’s Great Lakes/Atlantic Office in Ann Arbor, Michigan.