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[From Summer 1994]
Attempting to provide habitat for a diverse group of wildlife species during the year is a challenge which the Chincoteague Refuge staff gladly accepts. Wildlife management is definitely not an exact science, as management techniques are constantly changed to respond to natural events such as storms, droughts, heavy rains, and even the natural progression of nature itself. Visitors to the refuge this summer will see first hand the active management of the refuge impoundments, or moist soil management units, which are very important for large numbers of waterfowl, shorebirds and wading birds. These units were created by constructing earthen dikes which retain water; water control structures were placed in the dikes in order to provide the capability of changing the water levels within each unit. You have seen examples of these units to the left of Beach Road as you approach the beach, and in the center and around the edges of Wildlife Loop. In all, the refuge staff manages fourteen different units totaling some 2,600 acres.
Since its establishment in 1943, the refuge staff has been striving to provide optimal migratory bird habitat through various forms of wildlife management. The first dike was built in 1951, creating the refuge's first impoundment. The first water control structure was installed during 1952 with water manipulation beginning in the spring of 1953 and, with the exception of the drought years of the 1980s, continuing to the present. Impoundment management in the 1950s, 1960s and 1970s concentrated on providing wintering habitat for ducks, geese and swans; since then the management has expanded to include shorebirds and wading birds.
Water levels within units are manipulated seasonally for two main reasons. First, different groups of birds have different feeding requirements. Dabbling ducks prefer enough water to swim easily but shallow enough to allow bottom feeding. Wading birds such as herons and egrets prefer the deeper borrow ditches along the edges of the impoundments. Shorebirds concentrate on mud flats or very shallow water where invertebrates can be readily found.
Additionally, impoundment water levels are manipulated to maximize waterfowl food production. Many plants are important sources of food for waterfowl over-wintering on the refuge, as well as for those species migrating through the refuge. A gradual spring draw-down in some of the impoundments to an approximate 50% water level coverage provides moist soil conditions which encourage these plants to germinate and send out deep root systems allowing them to withstand summer drought conditions which often occur. This type of management is therefore termed moist soil management and has been used as a refuge management tool since 1989.
Manipulation of water levels is also used to retard the spread of undesirable plants and to encourage growth of desirable species. In addition, when the water has evaporated from the impoundments during the summer, certain units can be disked. Disking accelerates the natural process of returning organic material to the ground by turning the soil over, forcing dead plant material into the earth. As the plant material decays, invertebrates feed on the dead plants, allowing their populations to expand. In addition to increasing invertebrate populations, selected disking helps reduce undesirable plants, such as saltmarsh fleabane, enhancing opportunities for valuable food plants to grow.
Over the past 40 years of impoundment existence, the borrow ditches which were created at the time of construction have filled in. The ditches were formed when the bottom material was "borrowed" to create the dikes of each of the impoundments. As a result of the filling of these ditches, timely draw-downs of some of the impoundments have been affected. This summer an excavator will be used to clean out some of the borrow ditches where improved drainage conditions are most needed. In addition to improving moist soil management capabilities, this maintenance project will provide additional habitat benefits by retaining water much of the year which will provide a supply of fish, such as stickle-backs and mummichogs, for avian fish eaters and also provide a source of fresh water for all wildlife. Historically, these borrow ditches, which parallel the roads, provided excellent public viewing opportunities of a wide variety of birds. Certain special birds such as kingfishers, egrets, herons, cormorants, grebes, and coots preferentially use these ditches.
Maintaining the borrow ditches will encourage continued bird use and thus promote bird watching opportunities for the public.
So, when you visit the refuge this summer and see water levels receding, tractors disking and an excavator cleaning out borrow ditches, don't be alarmed; the refuge is managing these units to provide ideal habitat for migratory birds.
Bob Wilson,
Deputy Refuge Manager
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