Background: The Prairie Warbler, a rare songbird in Ontario, is a species of conservation concern due in part to its small population size. The majority of Ontario’s Prairie Warblers breed in sparsely-vegetated rock barrens along the southeastern shore of Georgian Bay and the species is found rarely along the southern edge of the Canadian Shield. The amount of shrubland where Prairie Warblers breed is thought to be declining and little is known about the distribution of this species across the transition zone between the Canadian Shield and the Mixedwood Plains, from Georgian Bay to the Frontenac Arch. This area, known as the Land Between, has been gaining increasing attention as a unique and ecologically significant region of Ontario. The Land Between has never been systematically surveyed for Prairie Warblers, leaving a critical knowledge gap regarding the species’ distribution in this region.
Project work: In 2015, BECO’s Research Scientist worked with the Canadian Wildlife Service to develop a statistical model showing the potential distribution of Prairie Warbler habitat in central and eastern Ontario. Model results suggested several substantial areas within the Land Between that could provide Prairie Warbler habitat. In June of 2015, BECO conducted preliminary field surveys in Queen Elizabeth II Wildlands Provincial Park, targeting areas that were identified by the model. No Prairie Warblers were detected during these surveys.
In May and June of 2017, BECO conducted field surveys in rock barrens with sparse and shrubby vegetation across the southern edge of the Canadian Shield, from west of Gravenhurst to Puzzle Lake Provincial Park, east of Kaladar. We surveyed 214 locations identified as potential habitat by the model and detected Prairie Warblers at only 5% of survey points (10 individuals). We also surveyed 16 historical locations across the southern edge of the Shield. We detected Prairie Warblers at 31% of these locations where the species has been recorded previously (7 individuals). Including anecdotal detections (i.e., individuals detected within our survey area but not at survey locations), we detected 37 Prairie Warblers in 2017. Ninety-five percent of the individuals we detected were concentrated in four areas.
Conservation implications: Overall, we detected few Prairie Warblers along the southern edge of the Canadian Shield in 2017, even though habitat conditions looked appropriate for the species at the majority of survey points. In addition, we did not detect the species at the majority of the historical locations we surveyed. Our results suggest that Prairie Warblers are likely uncommon in the region we surveyed. The ephemeral nature of Prairie Warbler habitat in some locations makes this species vulnerable to local extirpation due to ecological succession.
Results from our surveys provide new information about a rare species’ distribution in an under-surveyed region, improving our understanding of Prairie Warbler distribution in Ontario. The lack of detections across the southern Shield also underscores the importance of habitat conservation in areas where the species is known to breed. The data we collected, both detections and non-detections, can also be used to develop more accurate habitat models for future surveys and monitoring, and to help determine the habitat requirements of this rare songbird in Ontario.
In 2015, BECO conducted preliminary surveys in Queen Elizabeth II Wildlands Provincial Park.
In 2017, we conducted surveys across the southern edge of the Canadian Shield.
Support for the Prairie Warbler project was provided by The McLean Foundation, the Helen McCrea Peacock Foundation at Toronto Foundation, and a donation from Janet and Kenneth Dance.
A male Prairie Warbler sings his ascending song: “zee zee zee zee zee zee zee zee” from a red oak tree in his breeding territory.
Photo: Garth Casbourn
Prairie Warbler habitat
Examples from 2017 field surveys of locations occupied by Prairie Warblers. Along the southern edge of the Canadian Shield, Prairie Warblers are found in rock barrens with sparse and shrubby vegetation. The species is often associated with common juniper, oak, and white pine.