Obligate Grassland Breeding Bird Ecology on Islands and Mainland Habitats in the St. Lawrence River Corridor

Abstract

The decline of obligate grassland breeding birds in North America over the past 40 years has resulted in focused grassland management and conservation efforts, including in New York State. Thus, there is a need for knowledge of obligate grassland breeding bird habitat preferences and high-quality grassland bird habitat. The primary objective of my study was to evaluate the quality of two large islands in the St. Lawrence River, Galop Island and Ogden Island, as obligate grassland breeding bird habitat, by comparing their grassland bird communities to those present at two mainland sites, the Green Landowner Incentive Program (LIP) site and Whitehouse Point. I conducted double-observer bird point counts, and vegetation and arthropod surveys in 2015 and 2016. Bobolinks (Dolichonyx oryzivorus) and Savannah Sparrows (Passerculus sandwichensis) were the most abundant obligate grassland bird species across the four sites, and were two of five obligate grassland breeding bird species observed over both years. Total obligate grassland breeding bird and Bobolink abundance were higher at the Green LIP site, Ogden Island, and Whitehouse Point, and lower at Galop Island. Savannah Sparrow abundance was similar across all four sites during both years of study. I found that percent graminoid cover was the best predictor of total obligate grassland breeding bird and Bobolink abundance in both years, though it was a weaker predictor of Savannah Sparrow abundance. Variability in arthropod biomass appeared to have little effect on obligate grassland breeding bird abundance, but was high across all sites during both years. Ogden Island supported an abundant obligate grassland breeding bird community, but Galop Island requires focused management to facilitate conversion of shrubland and early successional forest to high-quality grassland habitat. The Green LIP site’s high obligate grassland breeding bird abundance highlights the importance of private land management in the conservation of obligate grassland breeding birds. My study indicates that large islands in the St. Lawrence River may provide high-quality obligate grassland breeding bird habitat if are managed to retard or prevent succession of grasslands into shrubland and forest habitat.