2026

The Cerulean Warbler (Setophaga cerulea) is a small (8-10g) North American wood warbler (Parulidae) that breeds in the northeastern United States and small portions of southeastern Canada, and winters in northern South America, primarily in the Andes (Buehler et al. 2020). This long-distance migrant is among the fastest declining North American forest songbirds, with population declines exceeding 2% annually over the past 50 years and an estimated cumulative decline of nearly 70% since the 1980s (Sauer et al. 2020). Many factors contribute to this decline across different parts of the annual cycle, with deforestation and habitat degradation on the breeding and wintering grounds considered to be a primary driver (Buehler et al. 2020).

In Canada, the Cerulean Warbler is listed as Endangered federally and Threatened in Ontario. Nearly the entire Canadian breeding population (<350 pairs) occurs in Ontario within two regions: the Frontenac Arch and the Carolinian region. The Frontenac Arch supports about 95% of the national population and contains the largest remaining tracts of mature deciduous forest habitat upon which the species depends. Climate change projections indicate that the breeding ranges of many North American wood-warblers are expected to shift northward, increasing the future importance of Frontenac Arch forests to the global Cerulean Warbler population (Pham et al. 2022).

The Federal Recovery Strategy for Cerulean Warbler outlines three broad strategies to aid in the recovery of this species in Canada: habitat conservation and management, monitoring and research, and outreach and communication (MECP 2022). The proposed project directly addresses ALL THREE strategies.

1. Habitat conservation and management: this project will result in more refined forest management recommendations for Cerulean Warbler habitat, that will inform forest management and land use plans by established Birds Canada partners in the Frontenac Arch and Carolinian regions. Confirmed partners include land trusts, Conservation Authorities, environmental organizations, provincial and federal governments, and municipalities.
2. Monitoring and research: this project will contribute to filling key knowledge gaps by conducting range-wide surveys on Cerulean Warblers in their most important Canadian breeding grounds. These surveys will improve the ability to detect short-term changes in population trends and distribution, refine critical habitat identification, and support future recovery planning. The data collected will be used to also examine landscape-scale and forest patch size effects on Cerulean Warbler occupancy in Ontario, helping to guide future habitat management and conservation actions. This work will also reduce knowledge gaps regarding demographics and improve the ability to monitor habitat trends, identify new threats, and estimate population size on the breeding grounds in Ontario.
3. Outreach and communication: in addition to the work mentioned about sharing with our strong network of habitat management partners, this project will also support Canadian participation on international working groups that target Cerulean Warbler conservation actions on its breeding, migration, and wintering grounds – enabling data from Ontario to be shared with partners across the Americas. Birds Canada is the only Canadian representative on the Partners in Flight Cerulean Warbler Technical Working Group, and the results of this project will help fill key knowledge gaps for full annual cycle modelling while ensuring that Canada and Ontario continue to have a voice in range-wide conservation actions on this important endangered species.

This project will support the protection and improved management of mature deciduous forest habitat within the Frontenac Arch and Carolinian regions of Ontario by working with private land managers, conservation organizations, and government agencies. Incorporating Cerulean Warbler habitat requirements into forest management and stewardship planning in Ontario will also benefit numerous other at-risk forest-dependent bird species sharing the same habitats, including Wood Thrush, Prothonotary Warbler, Acadian Flycatcher, and Louisiana Waterthrush.

Finally, this project will address important knowledge gaps through coordinated surveys and research on habitat and landscape-scale factors affecting Cerulean Warbler occupancy in Ontario. This work will improve the ability to monitor population trends, refine critical habitat identification, and guide future conservation and management initiatives across the province. The project will also strengthen international collaboration by ensuring continued Canadian participation and Ontario representation in range-wide Cerulean Warbler conservation activities. Information collected through this work will contribute to full annual cycle conservation planning across the breeding, migration, and wintering ranges – and highlight the population and work in Ontario at the international stage.