By J. Dale James, Ph.D.
Waterfowlers have a keen interest in the behavior of ducks and geese, especially during the fall migration and winter, when hunting seasons are open. What they may not realize is that these nonbreeding periods are also important times of year for waterfowl. In fact, research indicates that habitat quantity and quality on migration and wintering areas may influence waterfowl breeding effort and success the following spring.
Shortages of food and resting habitat during these periods could potentially make waterfowl more susceptible to disease, predation, and harvest, thus decreasing the birds' survival rates. Moreover, a lack of winter foraging habitat prevents the birds from accumulating the fat and protein reserves needed to produce eggs and meet the energy demands of incubation. In other words, winter food shortages could not only reduce the number of female waterfowl that return to the breeding grounds, but also decrease the breeding success of those hens that do return. As waterfowl managers, our ability to understand these "cross-seasonal effects" is essential to developing conservation programs in those landscapes that are important to waterfowl during the nonbreeding phases of their annual cycle.
Studies examining the storage and use of nutrients by female Arctic geese indicate that birds arriving on the breeding grounds with more stored body fat and protein have better reproductive success than birds that return to the breeding grounds with less of these reserves. Subsequent research on mallards in the Mississippi Alluvial Valley (MAV) found that wintering birds weigh more on average in years with abundant seasonal rainfall than they do during dry years. Abundant rainfall in the MAV provides more habitat and food in the region for waterfowl, allowing mallards and other dabbling ducks to more efficiently acquire body fat over winter. In addition, this study found that breeding success was higher for mallards in years following wet winters in the MAV.
More recent research on pintails wintering along the Texas Gulf Coast has confirmed that habitat conditions affect the birds' body mass in winter, as well as the timing of their spring migration and arrival on the breeding grounds. Pintails wintering in this region traditionally begin their northward migration in late February. Waterfowl researchers have found, however, that many pintails are remaining longer on their Texas wintering grounds than in the past, likely because the birds are unable to acquire the fat and nutrients required to depart earlier. This is of serious concern to waterfowl managers because research indicates that pintails arriving early on the breeding grounds lay larger clutches and have better nest success and brood survival than do birds arriving later in the spring.
Most of the research suggests that a cross-seasonal relationship exists between migration and wintering habitats and survival and breeding success in waterfowl. In fact, as mentioned earlier, studies of Arctic-nesting geese indicate a direct link between migration and wintering habitat conditions and the birds' ability to successfully nest and raise broods the following spring. This relationship was easier to quantify among Arctic goose species, which are extremely faithful to specific nesting locations. Doing the same for ducks has been more challenging, but new satellite-tracking technologies are now being used to better understand how breeding, migration, and wintering habitats are linked and how cross-seasonal effects may ultimately influence duck populations. This information will help Ducks Unlimited and its conservation partners continue to deliver effective habitat conservation programs for waterfowl throughout their annual cycle and across their vast continental range.
To learn more about how you can support DU's conservation work on key migration and wintering areas, see "DU's Regional Fundraising Initiatives" on page 36 of this issue or visit the DU website at ducks.org/DUinitiatives.
Dr. Dale James is manager of conservation planning at DU's Southern Regional Office in Ridgeland, Mississippi.
Conserving Threatened Wintering Habitat in Texas An area of specific importance to wintering pintails and other waterfowl is the Texas Mid-Coast. The loss of traditional foraging habitat in this region has significantly reduced this landscape's capacity to support wintering waterfowl. There is a particularly large deficit in the availability of freshwater wetland habitat, especially flooded rice fields, which are of crucial importance to wintering pintails. With the widespread loss of much of the region's natural prairie wetlands, well-managed rice fields provide essential alternative resting and feeding habitat for waterfowl. In fact, rice fields provide approximately 55 percent of the dietary needs and food energy for wintering waterfowl along the entire Texas Gulf Coast. Unfortunately, due to severe water shortages, rice production in this region has declined by 50,000 acres during the past two years.
Understanding how changing land use and water restrictions could lead to further losses of native prairie wetlands and rice field habitats, and how these losses could impact populations of pintails and other waterfowl, will be essential to DU and its partners in planning future conservation work. The Texas Prairie Wetlands Project (TPWP) is one conservation program that DU and partners administer to address habitat shortfalls in the Mid-Coast region. TPWP projects are conducted on private lands and receive "supplemental" irrigation water, which is vital to ensuring the availability of habitat for waterfowl and other wetland wildlife in this region. To date, DU and its partners have provided technical assistance or directly delivered habitat on more than 68,000 acres through the TPWP.