A study of waterbirds in Shanks Creek: An investigation on Smith Island, MD
Abstract
A&N Electric Cooperative provides electrical power to the communities of Smith Island via a distribution line that runs above water for approximately 1.8 miles along Shanks Creek. In 1999, a waterman reported observing a large number of Brown Pelicans falling from the power line near the mouth of Shanks Creek. The opinion was expressed that these birds may have been electrocuted when their weight caused two wires to make contact and complete the circuit. It has been further suggested that fish concentrations under the power lines may have led the pelicans to use them as hunting perches. The area surrounding Shanks Creek supports one of the largest communities of colonial waterbirds in the Chesapeake Bay. A report that power lines may pose a hazard to waterbirds has led to concerns on the part of both A&N Electric and the U.S. Fish and Wildlife Service. The broad objective of this study was to assess the magnitude and nature of the use that the distribution line receives from waterbirds. The association of waterbirds to electrical structures in Shanks Creek was monitored during 36 three-hour observation periods distributed among the relevant phases of the breeding cycle and tidal stages. A total of 3,623 observations of birds perched on electrical structures was made during the course of 432 surveys. Nearly 90% of these birds were perched on power poles and associated wooden structures with virtually all of the remainder perching on the top wire. The top wire serves as a guide and does not carry electrical current. Estimated loads experienced by wires averaged 2.1 Kg with a maximum observed load of 5.04 Kg. These loads are relatively insignificant and no visible depression of wires was observed. During 72 hours of direct observation, more than 4,000 birds were observed to fly across the power line within a distance of 10 m. None of these birds was observed to fly between wires or to strike any wire. There is no indication that waterbirds within and surrounding the Shanks Creek area experience any elevated risk of mortality compared to birds associated with the thousands of miles of exposed power lines found throughout the Chesapeake Bay and the broader mid-Atlantic Coastal Plain. No birds were observed to be electricuted during survey periods, no dead birds were detected during fieldwork, and no burn marks were observed along distribution lines. The suggestion that large numbers of Brown Pelicans are attracted to Shanks Creek for foraging and that they collectively perch hunt from wires was not supported by the observations made during the breeding season of 2000. In more than 100 hours of observation across the breeding season, only two pelicans were observed to contact any electrical structure. These included two young of the year birds that landed on the top wire for a period of approximately 10 seconds. Although many pelicans were observed to forage in Shanks Creek, they used the traditional methods of plunge diving and “seigning” in the shallows. The highest number of birds observed to be perched on a single wire span was three Double-crested Cormorants. These birds would have resulted in a combined load of 5.04 Kg. This load appears to be inadequate to result in a significant increase in the probability of a wire to wire contact.
