Evaluation of biological benefits and social consequences of Bald Eagle protection standards in Virginia
Management guidelines intended to protect Bald Eagles on private lands must attempt to strike a balance between benefits to the breeding population and the burden imposed on society. Since reaching a low in the early 1970s the Virginia Bald Eagle population has exhibited an exponential recovery with an overall ten-fold increase in breeding pairs. The dramatic recovery is placing a rapidly expanding burden on the regulatory agencies to implement current management guidelines and society to comply with guidelines. Protection standards currently in use were developed in an earlier phase of recovery when limited information was available. The primary objective of this project is to evaluate both the social and biological implications of current Virginia guidelines. Twenty-five years of Bald Eagle survey information was used to analyze trends relative to guidelines. Bald Eagle pairs in Virginia exhibit a 27% annual turnover rate in nesting substrate such that the number of nest structures is, on average, more than 40% higher than the number of breeding pairs. However, average life expectancy of nests at abandonment is only 1.46 years. Because there is a 3-year policy for declaration of an abandoned nest required for the dissolution of management buffers, the management standard that protects all trees containing any nest material seems to provide little value. Given the burden on regulatory agencies to track nest structures in order to implement this standard, a change in the guidelines should be considered. The 3-year rule regarding a determination of abandonment was established under the belief that there was a sharp decline in the probability of re-occupation following the third year. The probability distribution of re-occupation following nest abandonment approximates a continuous, negative exponential with no functional breaks. Although the probability that a pair will ever return after 3 years have passed is less than 10%, the probability after 2 years is only 13%, after 4 years is 7.5%, and after 5 years is less than 5%. Because there are no obvious breaks in the distribution, establishment of the length for a waiting period is somewhat arbitrary. Lands surrounding Bald Eagle nests that are considered under “management restrictions” have increased exponentially along with the breeding population. The economic value of these lands has also increased due to both the expansion of lands under restrictions and the increase in real estate valuations in recent years. In 2003, the collective value of lands within secondary management buffers surrounding active nests exceeded 1.7 billion dollars. The magnitude of this societal burden demands an effort to ensure that guidelines are both efficient and effective. Despite the evidence that Bald Eagles prefer to nest in areas away from human development, an increasing number of pairs are nesting in such locations. This study demonstrates that urban pairs represent a small fraction of the overall population. More than 80% of the population nests in areas with less than 1% impervious surface in management buffers. Only 5% of pairs nested in areas with more than 2% impervious surface. This study concluded that pairs breeding in areas with the highest coverage of impervious surface, were at least as productive as other pairs in the population.