Tiny devices known as geolocators, which track light levels and atmospheric pressure, are helping scientists better understand the migration patterns of small songbirds like the yellow-rumped warbler, or "butter-butt." These lightweight tools have enabled researchers to follow the long-distance journeys of birds that previously could not be easily tracked due to their small size and the limitations of older tracking technologies. The insights gained are helping to reshape our understanding of bird migration across North America. In the 1960s, scientists first used radio telemetry to track birds, requiring them to follow tagged birds with receiver equipment. This method was limited in range and practicality. In the early 2000s, satellite tags allowed remote tracking, but GPS devices were too heavy for most small birds. To overcome this, researchers developed light-level geolocators, which use a small battery, clock, and light sensor to estimate a bird’s location based on sunrise and sunset times. However, these devices can have errors of hundreds of miles and are less accurate near equinoxes. More recently, scientists have improved tracking accuracy by incorporating atmospheric pressure measurements. As birds fly, changes in air pressure are recorded, allowing researchers to determine when a bird takes off or lands. By comparing these pressure changes to global weather data using software like GeoPressureR, scientists can pinpoint a bird’s location with greater precision. Adding wind data to the model further enhances accuracy, offering a clearer picture of migration routes and behaviors. Using these multisensor geolocators, researchers studied the myrtle warbler, a northern subspecies of the yellow-rumped warbler that breeds in North America’s boreal forest. While some populations winter along the Atlantic and Gulf coasts, the wintering grounds of birds from the northwestern regions had been unknown. Historical records suggested these birds might breed in Alaska and British Columbia, but tracking confirmed that they migrate east across Canada’s boreal forest before heading south to the Gulf Coast, not the Pacific route previously assumed. This 6,800-mile journey is longer than expected for a species typically considered a medium-distance migrant. The findings suggest that some songbirds may follow migration routes encoded in their genetics, shaped by the movement of forests after the last ice age. This new geolocation method is improving our ability to track small birds, helping to identify critical habitats and threats they face throughout the year. It also provides data on the altitude of migratory flights, which is important for understanding risks like collisions with buildings or wind turbines. As more bird species are tracked using these tools, scientists are gaining a more complete picture of how small birds navigate and survive their long journeys.