By Tina Yerkes, Ph.D.
While the fall migration of ducks and geese is eagerly anticipated and closely observed by waterfowl hunters, the spring migration usually receives much less attention. This is unfortunate as the return flight of waterfowl to their breeding grounds is one of the most amazing spectacles in the natural world. Huge concentrations of ducks and geese gather in places like Nebraska's Rainwater Basin, the Klamath Valley on the California-Oregon border, and the upper pools of the Mississippi River as the birds push northward along the retreating edge of the freeze line.
The spring migration is also one of the most important yet least understood periods in the annual cycle of waterfowl. Our current knowledge of migrating and wintering waterfowl ecology suggests that food availability is the primary factor limiting waterfowl populations outside of breeding season. During spring, birds must acquire large amounts of nutrients to fuel their extensive travels and meet their energetic needs when they arrive on the breeding grounds.
Unfortunately, some of the most significant wetland losses in the nation—in excess of 80 percent—have occurred in the Upper Mississippi River watersheds, where waterfowl from both the Atlantic and Mississippi flyways migrate in spring. Given the large historic loss of wetland habitat in these regions, migrating waterfowl may not be able to acquire adequate food to meet their needs. And ongoing loss and degradation of remaining wetland habitat in these areas will only further limit the food resources available to migrating waterfowl. For example, recent research has documented that female scaup migrating through the Upper Mississippi River watershed have less body fat than they did 20 years ago. Since scaup and many other waterfowl don't appear to be leaving the wintering grounds in poor condition, loss or degradation of spring migration habitat and a resulting lack of food resources in these areas may be contributing to declines in scaup and other waterfowl populations.
As a result, increased protection and restoration of wetlands in key spring migration corridors may be warranted to achieve continental population objectives for scaup and other waterfowl species. But until recently, little information on the nutritional requirements and feeding habits of spring migrating waterfowl was available to direct wetland conservation and management efforts in these areas. Waterfowl biologists have assumed that increased foraging habitat will benefit waterfowl survival and body condition, and the quality of wetland habitat for migrating waterfowl in spring is determined by how much food this habitat provides the birds. Food availability, in turn, is associated with the type of wetland habitat and management actions that are applied to this habitat.
To address these important questions, Ducks Unlimited and many conservation partners recently conducted a multi-year, landscape-level study on the habitat needs of waterfowl during spring migration in the Great Lakes and Upper Mississippi River watersheds. Specifically, this study examined waterfowl food availability, diet, feeding habits, body condition, and nutrient acquisition during spring migration. Findings from this research will be used to direct future wetland management and protection work in these important waterfowl migration corridors.
To help ensure the findings would be relevant to the full spectrum of spring migrating waterfowl, researchers focused on five duck species with different body sizes, feeding regimes, migration habits, and breeding chronology. These ducks included mallards, scaup, gadwalls, blue-winged teal, and ring-necked ducks. We also chose six study sites that were representative of important spring staging areas (see map) across the Upper Mississippi and Great Lakes regions. At each site, food samples were taken in all wetland types, hens were collected and examined to determine their diet and body condition, and birds were observed in the wild to determine their feeding activity and use of different habitats.
Prior to this study, most waterfowl research focused on the birds' diet during the breeding season or winter. In general, ducks consume invertebrates high in protein during the breeding season, as protein acquisition is important for egg laying. During the fall and winter, ducks primarily focus on carbohydrates available in seeds, grain, and other plant foods to meet the energetic demands of harsh winter weather and fuel spring migration. The diet of spring migrating ducks has not been well documented, and it wasn't clear when ducks shift from a diet high in carbohydrates to protein as hens move north toward their breeding grounds. An understanding of diet and the factors that influence diet is important so managers can maximize production of preferred waterfowl foods in managed habitats.
What did we learn? Among hens in our study, invertebrate consumption increased and seed consumption decreased as the birds moved farther north. The proportion of invertebrates consumed by hens also increased as spring progressed in all species studied—although this varied significantly among species.
Some of the results were surprising. For example, we found that hen scaup consumed equal amounts of seeds and invertebrates on southern and mid-latitude study sites. And while consumption of invertebrates by scaup was higher on northern study sites, the birds consumed more seeds than had been observed in past studies at similar latitudes. Our research also found that gadwalls, considered the most vegetarian of the five species examined, still consumed mostly plant material during spring migration. Nevertheless, invertebrate consumption by hen gadwalls did increase as the birds moved north and spring progressed. Blue-winged teal consumed the greatest proportion of invertebrates of any species at southern latitudes, which was consistent with earlier studies in these locations. However, the proportion of invertebrates consumed by hen bluewings on our northern sites was lower than invertebrate consumption documented in past research in North Dakota, suggesting that hen bluewings continue to increase the proportion of invertebrates in their diet as they migrate north.
Our study also examined waterfowl food abundance in a variety of spring migration habitats. Food availability varied by wetland type and location. Food biomass estimates in these habitats were lower than at other times of the year, suggesting that wetland habitats have a lower capacity to support the energetic demands of ducks in spring than during fall and winter. Among habitat types, emergent wetlands provided the most seed and invertebrate food resources for waterfowl. But surprisingly, invertebrate biomass in flooded agricultural fields rivaled that of some natural wetlands. This result was quite unexpected and is worthy of further investigation by waterfowl managers.
Another important objective of our study was to measure the body condition of female ducks during spring migration. Examination of hens collected on our study sites revealed that levels of fat and protein in hens increased as the birds moved north, again likely because of increased consumption of invertebrates. In general, hens increased their nutrient reserves (protein and fat) as they moved north, suggesting that the birds acquire these reserves specifically to prepare for reproduction later in spring. As expected, hens collected at some locations were in better condition than hens collected at other sites, indicating that some areas may not have enough feeding habitat for the birds to acquire nutrients at optimal rates. The increasing preference for invertebrates among all hens studied suggests that waterfowl populations may suffer if invertebrate availability declines as a result of wetland loss and degradation on spring staging areas. Poor water quality in wetlands, which has a negative effect on invertebrate abundance, is one of the greatest concerns and challenges for waterfowl managers in the Upper Mississippi and Great Lakes watersheds.
What's the bottom line? Our research suggests that to meet the energetic demands of female ducks during spring migration, managers should provide a variety of shallow- and deep-water wetlands rich in both seeds and invertebrates sought by feeding hens. As you move north up the flyway, a greater emphasis should be placed on invertebrate production to meet the dietary preferences and needs of female ducks. Conservation practices and policies that protect existing habitat and improve water quality in wetlands, especially in the Upper Midwest, will help provide a more bountiful spring buffet for migrating waterfowl. And in doing so, we can help ensure that waterfowl will have a better chance of successfully nesting and raising young when they return to the breeding grounds later in spring.
Black Duck Migration Study Completed
Spring migration patterns and ties between breeding and wintering grounds were the focus of a parallel study on black ducks conducted by Ducks Unlimited and partners in the Atlantic and Mississippi flyways. In this research project, 68 hen black ducks were trapped and fitted with satellite transmitters across Ohio, Virginia, Delaware, New Jersey, and New York. These birds were then monitored throughout their annual cycle to determine their migration routes and breeding and wintering areas.
This work confirmed that most black ducks wintering east of the Chesapeake Bay breed in eastern Quebec and the Maritime Provinces, while black ducks that winter to the west of the bay breed farther inland, primarily in Ontario. During the winter, most hens remained close to their trapping location, indicating that the birds are faithful to particular wintering areas. The study also found that for black ducks, spring migration is more protracted, and the birds make more stops while migrating in spring than in fall. These results further support the need to provide high-quality spring migration habitat where black ducks and other waterfowl can acquire nutrients as they move north to breed.