5 minute read. |
By Erica Geldart and Lucas Berrigan
The Golden-winged Warbler is a tiny, brightly marked songbird with an epic journey—migrating thousands of kilometres each year between young savannah habitats across eastern North America and mid-elevation forests of Central America. Sadly, the species has declined by more than 60% in the past 60 years, primarily due to habitat loss, and to some extent genetic extirpation due to interbreeding with the more dominant Blue-winged Warbler. Costa Rica plays a critical role in its survival: nearly one in five Golden-winged Warblers spend the winter there.
Motus-tagged Golden-winged Warbler. Photo: Paz A. Irola
A new international study—led by researchers from SELVA: Investigación para la Conservación en el Neotrópico, the U.S. Fish and Wildlife Service, and Birds Canada—used the Motus Wildlife Tracking System to follow Golden-winged Warblers from their non-breeding sites in Costa Rica to their breeding grounds in North America. Recently published in Ornithological Applications, the study challenges long-held assumptions about bird migration while underscoring the importance of conserving Costa Rica’s humid mid-elevation forests.
Over the course of two years, the team fitted 69 Golden-winged Warblers with tiny Motus radio transmitters at five sites in Costa Rica chosen to represent areas with different amounts of rain and different levels of forest cover. They discovered that birds in drier, less forested habitats departed earlier but migrated more slowly, while birds in wetter, forest-rich habitats departed later but travelled faster—sometimes catching up to or even overtaking those that departed earlier.
The findings point to the conservation importance of wetter mid-elevation forests in Costa Rica, particularly those adjoining existing protected areas. But drier areas also matter. “Most females winter in drier habitats, and these forests have been especially hard hit by deforestation,” explains co-author María de la Paz Angulo-Irola. “They are in urgent need of restoration.”
Motus-tagged Golden-winged Warbler. Photo: Paz A. Irola
“Understanding how nonbreeding habitat influences migration strategies is essential to reversing the decline of Golden-winged Warblers,” adds co-author Sarah Kendrick. “Conservation must consider the full annual cycle, not just the breeding grounds.”
The study also tracked some warblers all the way back to their breeding grounds. Most followed a narrow flyway through the Midwestern United States. The majority were headed for the Upper Midwest—Minnesota, Wisconsin, and Michigan’s Upper Peninsula—with a handful linked to Ontario and the Appalachian Mountains.
“Being able to track a 9-gram bird across continents was once a dream,” says Stuart Mackenzie, co-author and Director of the Motus Wildlife Tracking System at Birds Canada. “Today, thanks to international collaborations and novel advances in technology, we can finally answer questions that are critical for conservation.”
The study also tracked some Golden-winged Warblers all the way back to their breeding grounds. Most followed a narrow flyway through the Midwestern United States. The majority were headed for the Upper Midwest—Minnesota, Wisconsin, and Michigan’s Upper Peninsula—with a handful linked to Ontario and the Appalachian Mountains.
This work was made possible through close collaboration between scientists and organizations in Costa Rica, Colombia, Canada, and the United States. “Hosting the team in Costa Rica was a real privilege,” says Ernesto Carman, who coordinated the fieldwork at several sites, including his family’s shade-grown coffee farm. “It was a remarkable learning experience and showed how conservation is built through partnerships.”
Motus-tagged Golden-winged Warbler. Photo: Paz A. Irola
Golden-winged Warblers are among the fastest-declining songbirds in North America. By revealing how winter habitats influence their spring migration, this study points to concrete conservation actions—protecting and restoring key forests in Costa Rica—to help secure their future. The findings also demonstrate how the Motus Wildlife Tracking System is a powerful tool helping to transform our understanding of migration and provide the information necessary to guide full annual cycle conservation across the Americas.
Learn more:
Read more about this research in Ornithological Applications: https://doi.org/10.1093/ornithapp/duaf036
Explore Motus data from this project: https://motus.org/dashboard/#e=profile&d=projects&s=441
Explore Motus data on this species: https://motus.org/dashboard/#e=profile&d=species&s=16420
State of Canada’s Birds: https://naturecounts.ca/nc/socb-epoc/species.jsp?sp=gowwar
Learn about other Motus research: motus.org/resources/applications
References:
Bayly N.J., Kendrick, S., Carman, E., Angulo-Irola, M.P., Caicedo-Ortiz, Y., and Mackenzie, S. al. 2025. Wetter and more forested nonbreeding areas result in later departures but a faster spring migration in Vermivora chrysoptera (Golden-winged Warbler). Ornithological Applications 127: 1–14. https://doi.org/10.1093/ornithapp/duaf036
Carman, E., A. Irola, P., Bayly, N. SELVA – Costa Rica (Project 441). 2021-2025. Data accessed from Motus Wildlife Tracking System, Birds Canada. Available: https://motus.org/. Accessed: 2025-08-19