Abundance Estimates for Marsh Bird Species in the Columbia Wetlands, British Columbia, Canada

Abstract. The Columbia Wetlands are one of the largest contiguous wetland complexes in western North America. Current population estimates are necessary for designation of priority conservation areas and for reliable assessment of population status for species of conservation concern. This multi-year study (2016–2019) was designed to estimate abundances of focal and secondary marsh birds using standardized call-broadcast protocols and distance sampling methods. Abundances of focal species varied by year, and mean population estimates indicated the most abundant secretive marsh birds were Sora (Porzana carolina; 4605 birds), followed by American Coot (Fulica americana; 2358 birds), Virginia Rail (Rallus limicola; 2124 birds), and Pied-billed Grebe (Podilymbus podiceps; 1657 birds). Most abundant secondary species were Marsh Wren (Cistothorus palustris; 6328 birds), Red-winged Blackbird (Agelaius phoeniceus; 5422 birds), Yellow-headed Blackbird (Xanthocephalus xanthocephalus; 884 birds), and Wilson's Snipe (Gallinago delicata; 445 birds). Habitat covariates for detection functions varied by species, tended to include woody vegetation, tall vegetation, and open water; supporting previous studies proposing that a ‘hemi-marsh’ state is an important habitat condition for many marsh bird species. The Columbia Wetlands provide important wetland habitat and these estimates underscore the need for effective management for the conservation of British Columbia’s avifauna.