This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Squinting through my binoculars, I scanned the dense branches of a black spruce, trying my best to catch a glimpse of the thin legs of a small black, white and yellow songbird. I was on the hunt for a yellow-rumped warbler—a bird affectionately called "butter-butt" by birdwatchers after the distinctive buttery yellow patch of feathers above its tail.
Once I spotted a flash of red on one of the bird's legs, I knew that this individual was special—in fact, it was one that I already knew well. That's because I had placed identifying bands on it the previous year as part of my Ph.D. research, and it was carrying a very important piece of new technology. I played the high-pitched "warble" of its song through a speaker placed below a mist net of fine, nearly invisible mesh.
Thinking another male had intruded on his territory, the bird quickly descended. My tactic worked—he got caught in the net. As I gently removed him, I breathed a sigh of relief as I saw the Tic Tac-size device sitting on his back.
Over the past year, this warbler carried a multisensor geolocator backpack throughout his migratory journey, recording the long trek from his breeding grounds in Anchorage, Alaska, to an as-yet-unknown winter refuge and back again. Working with my Ph.D. adviser, evolutionary biologist David Toews, I deployed dozens of these cutting-edge tags to illuminate the migratory journeys of these high-latitude breeding warblers at a scale not previously possible for small birds. Now, after a year of waiting, I finally had the data in hand.
Researchers began tracking the movements of migrating birds in the late 1960s using radio telemetry, a technique that requires tagged birds to be physically followed with receiver equipment, sometimes aided by a small aircraft. Then, as GPS became more widely available in the early 2000s, satellite tags let researchers accurately track birds remotely. However, GPS transmitters are hefty—even just the battery that powers them is too heavy to be carried by the majority of small migratory songbirds, which often weigh less than a spoonful of sugar.
To address this problem, researchers developed ingenious little light-level geolocators. These miniature tags minimize weight by containing only a tiny battery, clock, computer chip and light sensor. They store data internally rather than transmitting it—hence my need to recapture tagged birds a year later.
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