Despite these impacts, mallards enjoyed steady population growth in the Great Lakes states for several decades. In recent years, however, this trend appears to have reversed. Unsure of the cause of this population decline, Ducks Unlimited and the conservation community set out to clear up this uncertainty. Working in cooperation with numerous partners, DU recently completed an extensive three-year study to discover the root causes of declining mallard numbers in this region. Findings from this landmark study will help guide DU's conservation programs in the Great Lakes states for years to come.
The Great Lakes mallard study was borne out of necessity to eliminate uncertainty in habitat conservation programs for breeding mallards in these states. Modeled after extensive research in prairie Canada, this study was designed to determine what factors were limiting mallard population growth in this region. DU researchers trapped numerous hen mallards, marked the birds with radio transmitters, and followed them every day throughout the breeding season to record their movements, nest success, clutch size, brood survival, and habitat use—all things DU and its partners needed to know to determine what was limiting this population of mallards.
Beginning in early spring of 2000, field crews battled late-season snowstorms to trap female mallards as they returned and established breeding territories. Hens were collected by placing decoy traps containing tame hen mallards in the territories of wild birds. These traps work by exploiting the territorial instincts of breeding mallards. Hens attempt to drive away the intruder (in the trap) from their territory, and thus become trapped themselves. DU research scientists anesthetized the wild hens and surgically implanted a radio transmitter—roughly the size of a 12-gauge shotgun shell—in each bird's abdominal cavity, then released the ducks unharmed. This technology allowed the researchers to follow the daily activities of these otherwise elusive birds without disturbing them.
During each field season, research technicians used telemetry equipment to follow radio-marked hens from late March through the end of August, recording information such as habitat use and duckling survival. Over a three-year period, DU tracked a total of 560 mallard hens. Research sites were chosen to represent a variety of Great Lakes landscapes, from agriculturally dominated to predominately forested. Nine sites were selected throughout northwest and southeast Wisconsin; central and southern Michigan; the tri-state area of Michigan, Indiana, and Ohio; and in the Lake Erie marshes and northwestern corner of Ohio.