Pelagic Bird Survey on Lake Ontario Following Hurricane Isabel, September 2003: Observations and Remarks on Methodology

The abundance and dispersion of pelagic waterbirds was measured on Lake Ontario during the aftermath of the storm system generated by Hurricane Isabel, September 2003. The purpose of this study was to determine whether standard shipboard methodologies developed for surveying pelagic seabirds from ships on the ocean are applicable on the Laurentian Great Lakes, and if so whether such surveys may provide information that cannot be acquired from shore-based surveys. The abundance of waterbirds was low in offshore Lake Ontario, but similar to oligotrophic ocean environments. Our results suggest that bird surveys are easy to conduct from Great Lakes research vessels, and are likely to provide information useful for monitoring ecosystem health in the Lakes. INDEX WORDS: Birds, census methodology, ecological indicator species, Lake Ontario. *Corresponding author. E-mail: [email protected] INTRODUCTION Pelagic waterbirds, those that search for food far offshore on large bodies of water, are considered to be important indicators of the environmental health of the Laurentian Great Lakes (Hebert and Sprules 2002). Abundances of pelagic waterbirds are estimated by annual censuses at breeding colonies (many are colonial breeders) and by shore-based counts of birds on a lake (e.g., Gebauer et al. 1992, Weseloh and Pekarik 1999). A few studies have used offshore radio-telemetry of a small number of individuals to estimate the spatial dispersion of particular waterbird species on the Great Lakes (e.g., double-crested cormorants Phalacrocorax auritus on the western basin of Lake Erie, Stapanian et al. 2002). Doppler radar has also been used in counting birds, but has mainly proven useful for estimating the timing and abundance of migrating landbirds that fly across or around the Great Lakes (Diehl et al. 2003). In the world’s oceans, the abundance and dispersion of pelagic seabirds are estimated by censuses from ships, using standard, reliable survey methods (Tasker et al. 1984, Gould and Forsell 1989, Bibby et al. 2000). A very few studies have attempted to measure the dispersion of waterbirds on the Great Lakes from boats; the most notable surveyed western Lake Erie offshore regions within 10 km of the mainland or islands (Stapanian and Bur 2002, Stapanian and Waite 2003). We have searched the archives of the three principal North American ornithological journals (Auk , Condor , Wilson Bulletin); the species profiles of the principal Great Lakes pelagic species in the recent, authoritative Birds of North America series; the Journal of Great Lakes Research, and other relevant reference sources, and have failed to locate any published papers that directly estimate the abundance and dis-