Geolocators

Geolocators are small tracking devices used in wildlife studies to infer animal movements by measuring ambient light. They are typically attached to birds, small mammals, or marine reptiles and record light levels over time, providing position estimates when the device is recovered.

Most geolocators log daylight at set intervals. By determining sunrise and sunset times, researchers estimate latitude from day length and longitude from the timing of solar noon relative to universal time. After deployment, the device is retrieved and the recorded light data are converted into a sequential track.

Geolocators are lightweight and energy-efficient, often weighing from a few tenths of a gram to several grams, depending on species. They may include temperature or immersion sensors and store data until recovery. Real-time location is not provided; data extraction requires recapture or retrieval at the end of the study.

Limitations include relatively low spatial accuracy, often hundreds of kilometers, especially at higher latitudes. Cloud cover, shading, or topography can degrade light measurements, and equinox periods create ambiguity in latitude estimates. Because tracking is passive, researchers risk influencing behavior through device burden.

Applications span migration routes, stopover sites, and timing of movements; they are valuable for conservation planning when interpreted with uncertainty. Ethical considerations emphasize weight limits and permits to minimize impact, and data are typically shared with the research community for broader benefit.