Where do migrating birds stop to rest and refuel?

The annual migration of billions of birds, a journey spanning thousands of miles, has long fascinated and puzzled ornithologists. A critical aspect of this phenomenal journey is where these birds rest and refuel. This question is now being addressed in a new study by Fengyi Guo, a Ph.D. student at Princeton, and her team.

How to study bird migration

Fengyi Guo, along with colleagues from Princeton and the University of Delaware, has published a paper that utilizes weather radar imagery to map the migratory stopover sites of birds in North America. This innovative approach has enabled the team to identify over 2.4 million hectares of crucial stopover hotspots across the eastern United States.

Guo explains the methodology, stating, “Most landbirds migrate at night, lifting off from stopover sites after sunset. Weather radar captures this movement, but interpreting the data requires extensive processing.” The radar, sampling the atmosphere every 6-10 minutes, detects bird take-offs within an 80 km radius, providing intricate details of stopover habitats.

David Wilcove, a co-author and C-PREE faculty member, highlights the significance of this research. “Fengyi’s work gives us the first accurate picture of key stopover sites for birds across the eastern United States,” he says. This information is vital for identifying and protecting these critical sites to ensure safe passage for migrating birds.

Identifying resting spots for migrating birds

The study reveals that these hotspots are predominantly deciduous forests, including fragments in deforested regions. These areas are essential resting points for numerous landbirds annually. However, bird migration challenges remain. Only half of these protected hotspots are free from extractive resource use, and two-thirds lack formal protection.

Interestingly, the study found substantial seasonal differences in hotspot locations. The places where birds rest in the fall often differ from those used in the spring. With only 17% of hotspots being used in both seasons, the need for protecting a vast number of sites across the eastern U.S. becomes apparent.

The decline of migratory bird populations

Since 1970, migrating bird populations in the U.S. have declined by over a quarter, primarily due to human-induced factors such as habitat loss, overexploitation, and climate change. The authors of the paper emphasize the importance of protecting key habitats, noting higher stopover densities in protected areas.

The paper states, “A well-distributed network of well-protected stopover areas is essential to sustaining healthy populations of migratory landbirds in North America.” This network would complement conservation efforts on breeding and wintering grounds.

In summary, this study by Guo and her team marks a significant advancement in understanding and conserving migratory bird pathways. By leveraging the power of weather radar, this research provides a foundation for targeted conservation efforts, ensuring the survival and health of migratory bird populations in North America.

The full study was published in the journal Current Biology.

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