The contruction of dams across this country (and around the globe) has produced a variety of positive and negative effects. On the positive side, dams have been used to prevent flooding, provide a steady supply of water, produce electricity and create lakes for recreational activities such as fishing and boating. Negative effects have included the destruction of natural wetlands and swamp forests, the flooding of canyons and, though often unrecognized, the false security of placing residential and commercial developments on floodplains.
Here in the American Heartland, dams offer another advantage, especially during the winter months. By creating adjacent pools of deep and turbulent water, they yield open feeding areas for a wide variety of birds amidst a cold, frozen landscape. Large flocks of waterfowl often gather behind the dam, including divers such as mergansers, scoters and loons. Below the dam, where fish are stunned by the turbulence, bald eagles, great blue herons and a variety of gulls gather to glean prey from the surface; the common ring-billed and herring gulls are often joined by rare northern species that funnel southward as more northern waterways freeze over.
Of course, these dams also attract a variety of migrants during the spring and fall migrations, when flocks of black and least terns, Franklin's and Bonaparte's gulls, red-breasted mergansers, common loons, Mississippi kites, herons, egrets, white-faced ibis, cormorants and a host of swallows take advantage of fish and insects that congregate near and along these concrete barriers. Despite their negative impact on river ecosystems, dams can offer some damn good birding!
