Migratory landbirds of the lower Delmarva: habitat selection and geographic distribution
Abstract
Each year billions of landbirds migrate between the northern and southern hemispheres of the New World. During the spring and fall, migrants may be seen over most of North America. However, large numbers of these birds follow broadly defined routes known as flyways. Within these routes, significant physical barriers such as mountain ridges and large bodies of water act as migration bottlenecks concentrating large numbers of birds within relatively small land masses. These "concentration" areas may have tremendous conservation significance to bird populations that depend on them for rest, refueling, and protection from predators. For southbound migrants, the Chesapeake Bay is one of the largest physical barriers along the east coast. Migrants that reach the mouth of the Bay in the hours just before dawn settle out near the tip of the Delmarva Peninsula. On mornings following strong cold fronts, millions of birds may be concentrated near the tip of the peninsula. Because birds passing through the Eastern Shore are members of breeding communities throughout northeastern North America and winter communities throughout the Caribbean and Latin America, local land use decisions may have far-reaching consequences. Managing human population growth while conserving sensitive natural resources is a major challenge confronting land-use decision makers throughout the coastal zone. The two-year Northampton Migratory Bird Project (NMBP) was initiated under Northampton County's Special Area Management Plan (SAMP) to provide information to guide the development of enforceable policies that will protect and enhance migratory songbird habitat. This information will also be used in the development of a nature-based tourism industry. Several field projects were conducted between August and November of 1992 and 1993. The results that address the primary SAMP objectives suggest: 1. Both long- and short-distance migrants become concentrated within the lower 10 km of the peninsula, particularly along the shoreline of the Bay. 2. The majority of migrants appear to select habitats based on the density of understory vegetation. 3. Long-distance migrants pass through the peninsula in late summer and early fall, while short-distance migrants pass through the peninsula in mid to late fall. Management and policy implications are formulated for three general areas: 1. Zoning ordinances. 2. Vegetation protection standards. 3. Development of nature-based tourism initiatives.
