In 1899, scientists began tracking avian migration by placing a small ring with an identifier around birds' ankles. Researchers then had to recapture the birds elsewhere, leaving the journey between those points a mystery. Today, GPS tags allow researchers to see every stage of bird migration. The tags are small, have long-lasting batteries and solar panels, and track dozens of metrics. Migration is no longer described as just a theoretical range but rather as an exact map. Despite this technological advancement, the routes of many species in their respective flyways remain undescribed.