By Thomas E. Moorman, Ph.D.
Judging by the title, you might assume that this column is about how to prepare a healthy duck dinner for your family and friends. But, of course, that is wild game chef Scott Leysath's department. This column is about another type of duck salad—aquatic vegetation, on which many ducks thrive.
Waterfowl consume a host of aquatic plants, including various species of pondweed, southern naiad, wild celery, wigeon grass, coontail, and milfoil. Some of these plants are totally submersed and complete their life cycle without ever breaking the water's surface. Others have floating leaves or flowers, and some have both. Most are native to North America, although a few species of introduced exotic plants such as Eurasian milfoil are also consumed by ducks. In total, these plants represent at least 25 plant families and are important food sources for several species of waterfowl.
Nearly all of North America's ducks eat aquatic plants, at least opportunistically, and many species consume a largely vegetarian diet throughout much of the year. Gadwalls and American wigeon relish the leafy portions of aquatic vegetation. Green-winged teal, northern pintails, and mallards prefer the seeds produced by wetland plants. Canvasbacks, redheads, and scaup feed heavily on roots and tubers, while ring-necked ducks consume more leafy plant material and seeds.
Given the diverse food preferences of North America's ducks, an important objective for waterfowl managers is to conserve wetlands that offer the birds a variety of aquatic plant foods. Growing a salad buffet for ducks begins with healthy wetlands and suitable growing conditions. Good water quality, an appropriate range of salinity in coastal areas, adequate sunlight penetration to the pond bottom, appropriate water depth and wetland soils, and limited wave or current energy are all required to promote the growth and development of dense stands of aquatic plants.
Such conditions are especially common in the coastal ponds of the Gulf of Mexico. By late summer, the surface of these shallow, fertile wetlands can be covered with aquatic vegetation so thick that it looks as if you could walk on it. These duck salad–rich habitats are heavily used by migrating and wintering waterfowl, starting with blue-winged teal, which begin arriving in August, followed in the fall by other puddle ducks such as pintails, gadwalls, wigeon, and green-winged teal. It is also not uncommon for waterfowl, coots, and gallinules to consume nearly the entire annual crop of desirable wetland plants in these ponds by mid- to late winter.
Sadly, Louisiana has lost more than 1.2 million acres of its original coastal wetlands, including thousands of marsh ponds rich in high-value waterfowl plant foods. Due to the loss of these habitats and their accompanying food resources, the Louisiana Gulf Coast may now support 3 million fewer ducks than the region did during the 1970s. The causes of these wetland losses are complex, but ultimately the mainline levee system along the Mississippi River prevents fresh water, sediment, and nutrients from flowing into and sustaining the marshes. Once freshwater flows are reduced or eliminated, salt water from the Gulf filters into the marshes, killing aquatic plants and other vegetation that cannot tolerant high salinity levels. Over time, these degraded marshes eventually disappear, reclaimed by the open waters of the Gulf.
Farther west, in Texas, rapidly growing cities such as Austin, Houston, Dallas–Fort Worth, and San Antonio are straining the state's limited water supplies. This has reduced freshwater flows in many rivers that feed marshes and bays along the Gulf Coast. The results are similar to those in Louisiana—fewer marshes with suitable conditions for growing aquatic plants and fewer ducks wintering in the region. In addition, habitat loss and degradation may reduce survival among ducks that winter in the region, and when spring arrives, the remaining birds may depart their wintering grounds in less than optimal condition. This can delay not only the birds' arrival on the breeding grounds but also nesting, which may reduce waterfowl production.
The Gulf Coast's extensive marshes have been significantly altered and will likely always require active management and restoration efforts to sustain them. Conserving high-quality waterfowl wintering habitats—including marsh ponds rich in aquatic vegetation—is the objective of Ducks Unlimited's Gulf Coast Initiative. Through this effort, DU and its partners are working to restore coastal wetlands through freshwater diversions, the beneficial use of dredge material, development of water-control infrastructure, and other methods. DU also supports and advocates implementation of large-scale diversions of fresh water and sediment from the Mississippi River to rebuild coastal marshes in southeast Louisiana. Sustaining North America's most important waterfowl wintering area will require broad public support and a long-term commitment by all who value the Gulf Coast's threatened wetlands and the communities and traditions that depend on them. For more information about how you can support DU's Gulf Coast Initiative, visit the DU website at ducks.org/DUinitiatives.
Dr. Tom Moorman is director of operations in DU's Southern Region.