The lower Delmarva Peninsula is one of the most significant migration bottlenecks in eastern North America where large numbers of birds become concentrated within a relatively small land area. Habitats on the peninsula receives extremely high use by migrant landbirds during the fall months and is considered to have some of the highest conservation values on the continent. Past research has documented that the lower 20 km of the peninsula tip has a significantly greater density of birds compared to other areas. Over the past 20 years, blocks of private land have been acquired by the state and federal agencies for the purpose of restoring habitat for migratory birds. The conservation and management community has two distinctly different avenues available to improve habitat for fall migrant birds on the lower Delmarva Peninsula; 1) expand the amount of conservation lands through acquisition, private landowner agreements, and voluntary means, or 2) improve existing lands so they may support higher densities of birds through restoration. The purpose of this study was to establish a conceptual framework to place conservation progress and serve as a foundation for future efforts. The amount of land currently supporting forest cover represents only 30.3% of the study area suggesting that there is considerable opportunity to restore additional habitat to support migrants. Theoretically, there is space to triple the current footprint of forest habitat. Currently, conservation lands represent less than 14% of the upland landscape and support 16% of the total forest lands. Ongoing restoration projects will nearly double the value of conservation lands to forest migrants and will ultimately increase the existing forest habitat by another 16%. Despite its relatively small land mass, the study area is estimated to support more than 4 million bird days during the migratory period. In order to break even energetically, these birds would require nearly 30 metric tons of food. Current bird support represents only 25% of the landscape’s potential. Conservation lands are currently supporting less than 20% of the bird use within the study area. However, if ongoing restoration projects are brought to their conservation endpoints they would more than double this contribution. There are a number of information gaps that prevent a deeper assessment of conservation objectives for the lower Delmarva Peninsula. At the root of this gap is the need to better understand the standing crop of energy within forest patches. Energy is the most important currency to assess whether the Lower Peninsula is an energy source for birds (i.e., birds are provided with opportunity for a net energy gain) or an energy sink (i.e., the peninsula cannot meet energetic demands). Another information need is to a better understanding on the relationship between the standing crop and foraging rates of migrants. Taken together with conservation objectives, if resource demand of migrants is higher than what reference patches can produce then only solution is to increase land base to accommodate the number of consumers. However, this option has its limit within a confined landscape of the Lower Delmarva Peninsula.
Abundance/Distribution; Diet/Feeding/Energetics; Habitat Quality/Use/Movement; Migration; Conservation Planning; Adaptive Management/Limits
The Center for Conservation Biology Technical Report Series, CCBTR-13-05. College of William and Mary & Virginia Commonwealth University, Williamsburg, VA.
Watts, B. D. and M. D. Wilson 2013. Conservation limits and management opportunities for fall migrants along the lower Delmarva Peninsula. CCBTR-13-05. Center for Conservation Biology Technical Report Series. College of William and Mary/Virginia Commonwealth University, Williamsburg, VA. 25 pp.