By Kurt Anderson and John Coluccy, Ph.D.
Black ducks are the iconic waterfowl of the Atlantic Flyway. Once more numerous than mallards throughout this flyway, black ducks still migrate and winter in impressive numbers on the vast salt marshes that buffer the Atlantic Ocean and Chesapeake and Delaware bays. Black ducks are hardy and difficult to hunt. Especially wary of human presence, they have fooled and frustrated waterfowlers ever since the first English colonists settled at Jamestown. Among waterfowl, no other species is more revered by those who hunt them.
Sadly, population estimates suggest that black ducks have experienced a steady decline since the 1950s. In 1986, the North American Waterfowl Management Plan (NAWMP) established a population goal of 385,000 wintering black ducks. While the birds have shown recent increases on their breeding grounds, black duck numbers remain nearly 30 percent below the NAWMP goal. Several explanations for this have been proposed, chief among them overharvest, hybridization with mallards, habitat loss, and disease, but population models have failed to identify a single factor driving the black duck's decline.
Enter Ducks Unlimited. DU has launched a multiyear initiative to address the decline of black duck populations, including an extensive study using satellite tracking technology to learn more about the birds' migration habits. DU researchers captured 68 adult female black ducks during the winters of 2007–2008 and 2008–2009 in Delaware, New Jersey, New York, Ohio, and Virginia. These birds were outfitted with solar-powered satellite transmitters that were programmed to provide six GPS "fixes" each day. This data enabled researchers to track the birds' migration routes, identify major migratory stopovers, and examine habitat use.
DU researchers captured and attached satellite transmitters on hen black ducks before releasing them. (photo by John Coluccy, DU)
The single most important migration route for black ducks extends along the Atlantic coast from eastern Canada to Virginia. This corridor is followed by more than 50 percent of black ducks wintering in New Jersey, as well as a large proportion of black ducks that winter on the Delmarva Peninsula. Nine black ducks carrying satellite transmitters followed this route during the spring migration. The Hudson River Valley and St. Lawrence River are also used by migrating black ducks, and 10 birds in the DU study followed either one or both of these routes. Another important migration route extends from Ontario and western Quebec through New York to Chesapeake Bay. Most black ducks harvested along the western shore of Chesapeake Bay follow this migration corridor, and so did three black ducks carrying satellite transmitters in this study.
Two black ducks captured on the western shore of Chesapeake Bay migrated north through the Great Lakes region. One bird passed through Lake St. Clair, as did the majority of black ducks captured in Ohio. Many of these birds passed through Saginaw Bay and the St. Marys River of Michigan before crossing into Ontario. Interestingly, none of the black ducks captured in Ohio crossed into the Atlantic Flyway at any time during migration.
Only 13 black ducks in the DU study provided data during the fall migration. Of these, birds nesting in Ontario and Quebec began migrating south on October 25 and arrived on their wintering areas on December 4 (on average). In contrast, black ducks breeding in Labrador departed around October 5 and arrived on their wintering areas on approximately November 18.
HOMEWARD BOUND Two female black ducks captured in Ohio provided data during both years of the DU study. Remarkably, each bird settled on the same wetland on their breeding grounds that they had used the year before. This behavior is an example of philopatry—a tendency among waterfowl to return to the same breeding area—and emphasizes the need to consider connections between breeding, migration, and wintering habitats across vast ranges. Data from these two philopatric females also suggest that black ducks may spend more time on wintering areas and less time on spring stopovers than some regional management plans assume. Below:
Black ducks follow several different migration corridors between breeding and wintering areas.
Thirty-two black ducks provided data during spring migration. Average departure dates varied by state, with birds captured in New York leaving on March 28, Ohio (April 14), Virginia (April 14), Delaware (April 21), and New Jersey (May 22). The average arrival date on the breeding grounds was about two weeks earlier in the Mississippi Flyway (April 30) than in the Atlantic Flyway (May 17). This isn't that surprising given that black ducks captured in the Mississippi Flyway migrated a shorter average distance (501 miles) than those in the Atlantic Flyway (843 miles).
The number of spring stopovers made by black ducks in the DU study also varied by flyway: birds in the Atlantic Flyway stopped nearly twice as many times on average as those in the Mississippi. Although the length of time the birds spent on each stopover was nearly the same in both flyways, there was a positive relationship between the total distance the birds migrated and the number of, and total time spent on, stopovers. Simply put, black ducks in the Atlantic Flyway migrate farther, stop more, and subsequently spend more time on stopovers during migration.
When black ducks were grouped by latitude (North—New York and Ohio; South—Delaware, New Jersey, and Virginia), similar relationships persisted. One interesting finding was that southern black ducks migrated faster (by six miles per hour on average) than their northern counterparts, but still arrived on breeding areas more than two weeks later.
DU researchers also measured each black duck's body mass, which can provide a good indication of overall health. Mass was lowest among birds captured in the south and increased with latitude. Reduced energy reserves, prolonged migration, and delayed reproduction may be causing disproportionate declines among black ducks in the southern portion of their range.
While the results of this study were derived from a small subset of black ducks, the data will be used to help set habitat conservation objectives for black ducks during the nonbreeding period. DU and its partners are committed to implementing the results of this study and other research to conserve populations of black ducks and other waterfowl in North America.
Kurt Anderson is a DU biologist based in Annapolis, Maryland. Dr. John Coluccy is director of conservation planning at DU's Great Lakes/Atlantic office in Ann Arbor, Michigan.
PARTNERS IN RESEARCH DU would like to thank the following partners for their generous support for the black duck satellite tracking study: the Black Duck Joint Venture, Camp Fire Conservation Fund Inc., Cape May National Wildlife Refuge (NWR), Chincoteague NWR, Raymond and Barbara Dalio, Delaware Division of Fish and Wildlife, Edwin B. Forsythe NWR, the Herbert H. and Grace A. Dow Foundation, Moses D. Nunnally Jr. Charitable Lead Trust, New Jersey Division of Fish and Wildlife, New York State Department of Environmental Conservation, Ohio Division of Wildlife, Ottawa NWR, Prime Hook NWR, Suffolk County Department of Parks, the Nature Conservancy, the University of Delaware, Upper Mississippi River and Great Lakes Region Joint Venture, Virginia Department of Game and Inland Fisheries, Waterfowl Research Foundation Inc., the Winous Point Marsh Conservancy, and a host of other Major Sponsors.
For more information about this study and DU's Black Duck Initiative, go to www.ducks.org/conservation/black-duck-study.