Northern Prairie Wildlife Research Center
A relatively unknown alternative to satellite telemetry is the global location sensor (GLS) system (Wilson et al. 1992), which, while not a telemetry system, yields similar information. The GLS system uses a device attached to an animal that calculates the animal's position by changes in the ambient light intensity related to the season and time of day, and two fixes per 24-hr period are possible for up to 220 days. The GLS is appropriate only when large location error (150 km) is acceptable such as when studying migratory movements of far ranging, remote species like polar bears or wandering albatross. Although this system is even less accurate than satellite telemetry, it is much less expensive. The GLS unit costs only about $200, and there are no fees for data acquisition or processing. Additionally, the GLS unit weighs only 113 g. However, no data can be accessed until the GLS unit is retrieved. Thus if the GLS unit retrieval is not successful, all data are lost.