One afternoon in May 2008, a graduate student named Pat Kramer was in northwestern Pennsylvania catching purple martins. The bird, a large swallow that nests in artificial birdhouses across North America, is a well-studied species. But one particular purple martin Kramer and some fellow researchers from York University caught was about to revolutionize ornithology.
Kramer let an exclamation mark creep into his otherwise staid field notebook when he found it: “At 2:45p.m., Evelina captured Yellow 2551 in WH-43!”
Yellow 2551, the identification code assigned to this martin, was wearing a geolocator, a small device that uses a light sensor to calculate latitude and longitude and track a bird’s movement over time. The geolocator had traced this female martin’s migratory journey to Brazil and back via the Yucatan Peninsula. In doing so, it provided the first data on what had been a massive blind spot in the scientific understanding of the otherwise familiar purple martin: Where, specifically, does the bird go during migration? And what route does it take?
In the decade since Yellow 2551’s pioneering journey, scientists have used geolocators and a variety of newer technologies to gain an increasingly sophisticated understanding of how migratory songbirds move across the globe. As a result, a much more nuanced picture has emerged of how conditions on wintering grounds and along migration corridors affect birds’ survival. And very soon, with the deployment of some cutting-edge gadgetry on the International Space Station, ornithologists will finally be able to delve into the most disturbing mystery of all: why half of the migratory songbird species in North America are disappearing at alarming rates.