Investigation of bald eagles within the Rappahannock River Concentration Area
During the summer months, the Chesapeake Bay supports an estimated 1,000 migrant Bald Eagles from breeding populations in Florida and elsewhere in the southeast. These birds move into the Bay in mid to late May after their early breeding season is concluded and remain in the Bay until late summer. While in the Bay, migrant eagles congregate in 6-8 "concentration areas" where they forage and utilize communal roosts. The number of summering eagles using the Bay has increased dramatically over the past 20 years, reflecting the recovery of southeastern breeding populations. Over this same period, the human population surrounding the Bay has increased tremendously placing unprecedented demands on the tributaries of the Bay for recreational activities. The simultaneous increase in eagles and humans has heightened concerns about potential interactions and conflicts between these two user populations. In the summer of 1998, an investigation was initiated to collect data for the purpose of: 1) redefining the boundaries of the Rappahannock River Bald Eagle Concentration Area, 2) determining the current level of human use within a section of the Rappahannock River, and 3) investigating potential interactions between the human and eagle populations during the summer months. These objectives were accomplished using a series of extended shoreline surveys. The section of the Rappahannock River between Tappahannock and Port Royal supports a large population of Bald Eagles during the summer months. Use of the river by this population has increased substantially since the mid 1980's. The peak count of 232 eagles on 27 June represents the highest number of eagles ever recorded within this concentration area. The Rappahannock River Bald Eagle Concentration Area is currently the second largest summer concentration area known in Eastern North America. Elevated eagle numbers may now be observed along a substantial section of shoreline. In addition to the increase in eagles, an increase in both the number and distribution of known sites used for communal roosts was documented. Two new communal roosts were located. It is expected that four communal roosts occur within the concentration area. Currently, people using the shoreline are primarily associated with: 1) waterfront developments, 2) piers and boat ramps, and 3) parks and campgrounds. The number of people using the shoreline was twice as high on weekends compared to weekdays. Human and eagle use of the shoreline do not appear to be compatible. Shoreline areas with high human use have low eagle use and areas with high eagle use have low human use. Pairwise comparisons within a series of shoreline segments show that human use of segments has a significant negative influence on eagle density. However, eagle disturbance caused by people along the shoreline is not currently widespread and appears to be limited by the relatively low number of points where people have access to the shoreline. On average, boat activity was eight times higher on the weekends compared to weekdays. Eagles perched along the shoreline are sensitive to boat activity within 200m of the shoreline. As was the case with humans, near-shore boat activities are not compatible with eagle use of the shoreline. Unlike humans, river access points do not limit the distribution of boats. Once on the water, most boats can easily access many nearshore areas. Compared to other boat types observed, bass boats seem to be predisposed to eagle disturbance. All aspects of their "behavior" lead to a higher potential for the disturbance of eagles along the shoreline.