Published in Methods in Ecology and Evolution, this research led by Luke Halpin provides the first large-scale assessment of the spatial accuracy of modern geolocation algorithms under field conditions and suggests practitioners adopt a dynamic approach to estimating spatial uncertainty.
Light-level geolocators have greatly increased in usage as bio-logging tools due to their size and practicality. Despite their increasing application, there is a lack of concrete knowledge regarding their accuracy against a number of different factors. Thus, Luke conducted a field test of spatial accuracy by synchronously deploying light-level geolocators with GPS loggers on individual seabirds from around the world.
When cross-checked against high precision GPS loggers, Luke found that geolocator spatial accuracy was lower than the ~200km often assumed in studies. Spatial accuracy was found to be significantly affected by several factors, including species, geolocator model, and the geolocation package used. The strongest predictor of spatial accuracy was the expected inter-twilight period (i.e., the duration of day or night between sunrises and sunsets, or vice versa), where increasingly equatorial solar profiles, both temporally and spatially, induced larger error. Thus, light-level geolocators can be expected to have lower spatial accuracy during periods of solar equinox, as well as when tracked animals move nearer to the Equator.
“Based on our results, we urge greater caution and consideration of the limitations of light-level geolocation when using geolocator data to draw inferences about regional spatial use and behavior of wide-ranging marine species,” writes Luke. However, the study provides a simple function that practitioners can apply to their own geolocation datasets to assess the relative spatial accuracy of their data year-round.
Halpin, L. R., Ross, J. D., Ramos, R., Mott, R., Carlile, N., Golding, N., Reyes-González, J. M., Militão, T., De Felipe, F., Zajková, Z., Cruz-Flores, M., Saldanha, S., Morera-Pujol, V., Navarro-Herrero, L., Zango, L., González-Solís, J., & Clarke, R. H. (2021). Double-tagging scores of seabirds reveals that light-level geolocator accuracy is limited by species idiosyncrasies and equatorial solar profiles. Methods in Ecology and Evolution, 12, 2243–2255. https://doi.org/10.1111/2041-210X.13698