Of Men and Marshes

3. of marshes and summer

3, of marshes and summer To know what summer really can be on a north-central glacial marsh, one must go either westward or northward from Iowa--or, better, northwestward into northeastern South Dakota. A century ago, Iowa's marshes may have been like those to the west, north, or northwest. Old paintings of pre-settlement Iowa prairies have lark buntings perched on the horns of bison skulls, big shore birds distributed over the landscape, and other types of life that we now seldom find before we leave the state. The marshes of northwest Iowa resemble most closely those of the South Dakota of my youth, but little that I have ever seen in Iowa compares with what was once commonplace a few hundred miles away. Iowa's marshes do have eastern and southern features that myoid South Dakota marshes lacked. I never saw in South Dakota the white American egrets standing around in late summer, nor the wood ducks summering by the hundreds in the reedy and rushy marsh centers, nor the thousands of least bitterns that I have seen in Iowa. It is also on Iowa rather than on South Dakota sloughs that I have seen non-breeding hooded mergansers spending the breeding months and colonies of night herons nesting in the marsh itself instead of in the trees. Some of these differences over the north-central region may but reflect an observer's opportunities or the local changes in distribution of this or that species over the years. In other cases, the nature of marshes and summer 21 of the plant and animal life and the adjustments of living things to special kinds of environment bring change. Populations may be expected to thin out as their requisites become scarce toward the edges of their range. No species thrives where it does not belong. There are also the teasing questions of environmental niches and competition between closely related species. The black duck is the mallard's counterpart over much of eastern North America, and, where the ranges of the two overlap in the north-central region, we generally find one thriving much more than the other. To the west, we have the breeding range of the blue-winged teal merging with that of its western counterpart, the cinnamon teal, with places in their common range where the proportions of nesting bluewinged and cinnamon teal are highly variable. Among the other factors that may determine what lives where and when are droughts that force adjustments in ranges, but not all adjustments are so patently forced. Increasing populations of migratory birds may return to a given locality to breed after special nesting traditions have been established. Or, tracts of otherwise suitable habitat may long remain unfilled, if the birds lose their traditions for nesting there. Certain differences are nevertheless characteristic of different. parts of our region, and these may be maintained over periods of years, irrespective of ordinary annual variations in marsh life. Perhaps the marshes of northeastern South Dakota have so noticeably greater a variety of marsh birds than do central and northern Iowa marshes largely because of their location deep in extensive marshland areas. On a marsh-by·marsh basis, northeastern South Dakota would not seem to offer perceptibly better environment to, let us say, nesting pintails than places that offer similar water, vegetation, and terrain in Iowa; but, to the pintails, Iowa is edgeof ·range, and northeastern South Dakota is in the midst of favored nesting grounds. • No one view could typify a marsh of eastern South Dakota at its life-rich summer best. One view should be of a misty morning with sunlight filtering through, and avocets, willets, and lesser shore birds running along a mud flat, feeding, raising their wings (the willets showing their white bars) , and calling. On mud- or sandbars or floating posts or muskrat lodges, the terns guard their terri22 of marshes and summer tories. Over all, the medley of blackbird and bobolink calls, of coot and rail and grebe calls, the pumping of bitterns. In the right places, the booming of prairie chickens is a part of the morning sounds of early summer. Ducks are much in the marsh picture. Territory-holders sit along shore or on prominences out in the marsh, sometimes both members of the pair, sometimes the males alone. Here they are, nesting in the Dakotas, many of the ducks that were spring migrants through Iowa...