A New Way to Track Migratory Songbirds

Until recently, small migratory songbirds, too small to track via satellite, have eluded scientists who wish to follow their annual migrations. Now, a tiny device that senses light levels and records sunrise and sunset times, enables scientists to gain new, detailed insight into songbird migration.

The device, referred to as a 'light-level geolocator', is made of plastic and weights about 1.5 grams. To use it, scientists must first capture several individual birds that they wish to track and attach the geolocators to each bird. They then release the birds back into the wild and wait for the birds to complete their migration. Later, scientists recapture the birds and retrieve the devices. The data is downloaded from the devices and the sunrise and sunset times are analyzed. The sunrise and sunset times are used by scientists to calculate where the birds were at different points during their migration.

Bridget Stutchbury, a professor of biology from York University, Toronto, was the lead author of the study. Stutchbury's team used the the light-level geolocator devices to map the migratory routes of two species, purple martins (Progne subis) and wood thrushes (Hylocichla mustelina). In addition to pioneering a new way to track small birds, the team was able to establish data on the songbirds' speed of migration. They found that the birds migrated more than 300 miles a day, far more than the 90 miles per day that had previously been estimated.

Find out more: Stutchbury BJ et al. 2009. Tracking Long-Distance Songbird Migration by Using Geolocators. Science. Vol 323(5916) p 896.

Photo (top) courtesy of Elizabeth Gow. Male wood thrush with a geolocator.

Photo (bottom) courtesy of Tim Morton. Female purple martin with geolocator on her back.