Tiny backpacks reveal the secret, sometimes circuitous migrations of small songbirds

Researchers tagged migrating yellow-rumped warblers breeding near Anchorage, Alaska with tiny multisensor geolocator backpacks that record light and atmospheric pressure to track movement without needing a transmitter. Recapturing a tagged bird a year later, the team found the warblers didn't take the shorter Pacific Coast route to California as long hypothesized.

Instead, the tracked birds flew east across Canada's boreal forest before turning south to the Gulf Coast, a roughly 6,800-mile round trip. Researchers suggest the roundabout route reflects ancient glacial patterns that shaped how migration routes became genetically encoded over time.

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