Discovering the Chesapeake: The History of an Ecosystem

FIFTEEN: Bird Populations of the Chesapeake Bay Region: 350 Years of Change

chapter fifteen Bird Populations of the Chesapeake Bay Region 350 Years of Change james f. lynch The distribution and abundance of birds in the Chesapeake watershed in the last 350 years has altered according to species-specific responses to environmental changes occurring since European settlement. Deforestation, hunting, loss of submersed aquatic vegetation in the Bay, introduction of exotic species, and environmental contamination have had major effects on birds. The future of birds and other wildlife depends on measures taken to protect their habitat in the watershed and estuary. As seventeenth-century European colonists transformed the landscape of the Chesapeake Bay area, many bird species retreated westward. A few disappeared completely from the region. Other species remained widespread but in lesser numbers. In contrast, some birds profited from the man-made changes in their environment, and their numbers and geographic ranges increased. Losses of native bird species were balanced, numerically if not ecologically, by the arrival of exotic species that successfully established themselves in the wild. Not all historical changes in bird populations can be linked directly to human causes, but no bird species could have been unaffected by the tide of environmental change that swept over the Chesapeake Bay region during the past 350 years. In this chapter I identify the historical factors that seem to have had the greatest effect on birds in the Chesapeake Bay watershed. I describe a few examples in detail but do not attempt to trace population trends for all of the hundreds of bird species that are found, or formerly were found, in the Bay region. I emphasize Maryland and the District of Columbia , where birds have been more intensively studied than elsewhere. My focus is on two broad ecological groupings of birds: landbirds that inhabit the forests and fields of the watershed, and waterbirds that make use of the Bay, its tributaries, and fringing wetlands. The Historical Record The fossil history of birds in the Chesapeake Bay region has been discussed by Steadman (Chap. 5), who also addresses the zoogeographic affinities of the local avifauna. Stewart and Robbins have summarized the history of ornithological work in Maryland and the District of Columbia . Quantitative historical information on the Bay region’s birds is practically nonexistent until well into the nineteenth century, by which time major changes in abundance and distribution had already occurred. Earlier descriptive accounts mainly concern species that were heavily hunted for food, such as ducks, geese, swans, wild turkeys, and passenger pigeons. Two centuries after the arrival of the first English colonists, Warden in 1816 listed only 32 bird species known in the District of Columbia and adjacent Maryland. By the time of the Civil War, the District’s bird list had grown to 226 species; by 1918 the number had reached 286.These figures reflect an increase in the number of competent observers, as well as the steady accumulation of records on rare or sporadically seen species. Generally speaking, the statement by a reliable observer that a bird species occurred at a given place and time constitutes strong evidence of the species’ presence, but a lack of comment does not mean that species was absent.Thus, Warden’s failure to mention a number of species common at present, like the song sparrow or the Carolina wren, does not mean that those species were absent in 1816, but the inclusion on his list of both the passenger pigeon, now globally extinct, and the loggerhead shrike, now locally extirpated, is evidence that they were still around in the early nineteenth century. The dearth of early historical information forces us to infer the eighteenth - and nineteenth-century status of most bird species by combining knowledge of their current ecology with information about historical land-use changes. Given that about 90% of the Chesapeake Bay watershed was forested at the time of European contact, most forest-dependent birds must have been more abundant and widely distributed then than they were to become centuries later, when more than 75% of Bird Populations 323 the original forest would give way to cropland and pastures. Conversely, birds whose preferred habitat is open grassland or savannah were presumably scarce or absent in presettlement times and have subsequently spread throughout the region as the forest was cleared. Some population 324 Discovering the Chesapeake Fig. 15.1. Audubon painting of passenger pigeons (Special Collections, Milton S. Eisenhower Library of the Johns...