We evaluated the proximity to development of 2 representative groups of colonial waterbirds present in Maryland's coastal plain, active in 1985 through 1988, to determine the influence of land and water development on the distribution of waterbird nest sites. Thirty of 38 known common tern (Sterna hirundo) and Forster's tern (S. forsteri) colonies were located on marsh islands. All 23 great blue heron (Ardea herodias) colonies were located in forested areas usually along shorelines. The distance to and quantity of various man-made structures (e.g., buildings, roads, piers, agricultural areas) within 1 km of each colony were quantified from aerial photographs. Similar measurements were taken from randomly selected sites of potential nesting habitat. Development around the colonies was compared to the random sites using /-tests. Most of the 8 variables in the analysis were useful in differentiating between colony and random sites. Mean distances between colonies and all development categories exceeded 0.7 km. Both tern and heron colonies, on average, nested further from man-made structures and in areas less densely developed compared to random sites. We recommend establishing minimum buffer zones of 0.7 km and 1.5 km around great blue heron and common tern colonies, respectively to development. These buffers were based on the minimum average distance to the nearest building.
