Geolocator: Tracking migratory Birds

A miniature light level logger (geolocator) for tracking animal movements for long periods has been designed and developed by engineers at the British Antarctic Survey, but is now under license to UK company Biotrack (as of November 2011).

The devices can be used for tracking over long distances in any application where the logger usually has an unobscured view of natural light level at dawn and dusk. The loggers must be retrieved for data download.

The light level geolocator is a miniature, light weight archival tag recording essential light level information which can be processed to give location latitude and longitude.

The devices are small, have low weight and drag, long lasting and cost effective. Although not as accurate as GPS or ARGOS, this method allows a much cheaper and much smaller device to be constructed which records for a far longer time (many years).

For seabirds, logging of wet/dry information and sea surface temperature can also be included. The wet/dry recording has been developed to measure the activity of the birds, and the temperature information, when correlated with satellite data, can be used to improve the location fix.

The loggers work worldwide wherever there is dawn and dusk, and have been used so far on a number of species including geese, albatross, penguins, shearwaters, gannets, skuas, fulmars, ducks, shags and seals.

Being so small, they can be attached to leg rings of larger seabirds, thus avoiding problems associated with platform gluing and harnesses.

Accuracy is in the region of +/-150km and uncertainty is caused mainly by shading (including cloud and foliage), interference (non direct sun and artificial light), and for latitude, proximity to equinox and the equator.

Now that the current devices weigh in under 1.5g, use of them to track songbird species is now beginning to be explored.

A leg-loop harness, similar to the Rappole-Tipton method has been favoured so far. For back mounting with a harness, the supplier has developed devices with the light sensor on a stalk to clear the plumage of the bird.

Arctic Tern migration revealed here

For a great article from Kent McFarland of the Vermont Center for Ecostudies detailing recent use with passerines, see here