Retrospective comparison of the distribution and abundance of breeding Prairie Warbler (Setophaga discolor) along eastern Georgian Bay, Ontario, Canada

Abstract

Species inhabiting rare habitats or unique geographic regions may be underrepresented in standard surveys. More intensive, periodic surveys may be required to improve data quality, especially for species of conservation concern. Prairie Warbler (Setophaga discolor) has experienced range-wide declines of >50% in recent decades and is a species of conservation concern in Canada. The largest continually occupied breeding population of this species in Canada occurs along the shoreline of eastern Georgian Bay, Ontario, where annual Breeding Bird Survey and eBird coverage is generally poor. In 2015, we replicated a spatially intensive 1997 survey of this species along the eastern shore of Georgian Bay, visiting the same sites and using comparable methods. We detected more male birds at the survey sites in 2015 (estimated >350 breeding pairs) than in 1997 (estimated 265 breeding pairs). We also surveyed sites farther north than those covered in 1997, but the breeding range appears not to have moved substantially northward. We also conducted additional surveys and canoe transects in the core range in southern Georgian Bay to ensure that breeding birds were not being missed. Combining data from all our surveys in 2015, we estimated a total of 427 singing males in eastern Georgian Bay. Although overall numbers here appear to have increased in recent decades, localized declines in some areas warrant further investigation. The population appears to be stable or increasing in this region, but we recommend intensively re-surveying this population on at least a 20-year basis.