By Tom Moorman, Ph.D.
Ten thousand years ago, planet earth was undergoing yet another swing in a continuous series of climate changes. This time, a period of warming was under way that spelled the end of the most recent Ice Age. So what? you say. What has this to do with bottomland forested wetlands?
Well, if you are a waterfowler, and have an interest in the natural history of waterfowl and their habitats, then you have benefited in more ways than one from this period of climate change. Not only did the retreating glaciers shape the northern Great Plains, leaving behind countless prairie potholes of the Duck Factory, but as all that ice melted, much of the runoff rushed southward, forming a vast river that gave birth to what Native Americans called “Mississippi,” which, legend has it, translates to Father of Waters.
That’s an appropriate moniker, as the glacial runoff gave birth to an enormous floodplain that we know today as the Mississippi Alluvial Valley (MAV). Over several thousand years, as the period of warming continued and the glaciers retreated, the volume of runoff declined, and an intricate secondary network of rivers and swamps developed on the face of this roughly 24-million-acre floodplain. Ultimately, the soils, climate, flooding regime, and other factors combined to shape one of the most unique forested wetland systems in the world, called by some the Amazon of North America, and known regionally as the Delta.
This by-product of the last Ice Age became the most significant wintering area for mallards in North America, with upwards of 40 percent of the mid-continent population settling in the region’s network of sloughs, cypress-tupelo brakes, and, in some years, flooded oak flats. The key attraction for mallards was that at least one or more of the river systems in the MAV typically flooded annually, providing predictable habitat in the unpredictable world of wetlands.
Such annual winter floods created, in all but extreme drought years, hundreds of thousands of acres of flooded forested wetlands. These areas typically provided abundant, high-energy food, particularly acorns from several species of oak trees uniquely adapted to this system, including pin, water, willow, and Nuttall oaks. Acorns are loaded with carbohydrates, and because ducks don’t have to concern themselves with the Atkins Diet, or any of the other diet plans on the market these days, acorns are a food that ducks can readily convert to fat. For ducks, fat is the substance upon which their very survival depends.