Perceptibility of Prairie Songbirds Using Double-Observer Point Counts

Few studies have evaluated techniques for estimating detectability of prairie songbirds. We conducted dependent double-observer point counts at 52 plots in prairie pastures in southern Alberta, Canada, in 2012, to test for species-specific, group-specific, and observer-specific differences in perceptibility. Although we did not find strong species or observer effects on perceptibility of most species in the study, we found evidence of differences in perceptibility when we pooled prairie songbirds into groups according to singing behaviors. Observers typically perceived only 40% of quiet songbirds singing from the ground (e.g., grasshopper sparrows and horned larks) but observed >89% of louder species singing from perch sites (e.g., Savannah sparrows) or in flight (e.g., Sprague’s pipits). Dependent double-observer methods would result in little increase in accuracy of abundance estimates for most species, but could be useful in studies where quiet species are more abundant or are targets for conservation management.