To inform the design of targeted, species-specific surveys of Prairie Warbler (Setophaga discolor) in Ontario, Canada, we used autonomous recording units (ARUs) to document patterns in male vocal activity. We deployed recorders within the territories of breeding males at coastal sites near Georgian Bay, and at inland sites near Kaladar, in June 2015 and 2016, respectively. Although coastal and inland sites are <250 km apart, we observed distinct differences in the patterns and frequency of male singing. Overall, the mean number of songs per minute of males at inland sites near Kaladar was nearly triple that of coastal sites near Georgian Bay. Daily singing activity peaked shortly after sunrise and declined throughout the day at both sites. Daily singing activity was uniformly high across the entire morning period at coastal sites, whereas at inland sites the highest rates of singing were during the post-dawn morning period. Singing activity varied by chronological day at inland sites, with distinct peaks at the beginning and end of June. Singing at coastal sites did not vary by chronological day and was consistently low throughout June. Although our sample sizes are small, with minimal replication, we discuss our results in the context of reduced pairing success and male-biased sex ratios in small, isolated populations. In addition to documenting singing activity patterns to optimize future surveys for species of conservation concern, ARUs may also signal potential demographic differences important for population persistence that warrant further exploration.