Songbirds wear mini-backpacks for migration research

Researchers have equipped yellow-rumped warblers (also known as 'butter-butts') with tiny, Tic Tac-sized geolocator backpacks to map their migration routes. The birds breed in northern Alaska, and the new multi-sensor tags measure air pressure and light to track their journey to previously unknown wintering sites. Earlier methods such as radio telemetry and GPS transmitters were too heavy for small songbirds....