Synchronous monitoring of vulture movements with satellite telemetry and avian radar

Radar and satellite global positioning system-platform transmitter terminal (GPSPTT) transmitters provide complementary information on the movements and behaviors of individual birds. The GPS-PTT tag provides a snapshot of altitude and location of a specific individual of an identified species at predefined intervals. The history of the individual is known because each transmitter has a unique identification code. The radar cannot identify individuals or even species but it provides continuous position reports (altitude and location) of birds within its detection range. By integrating data from the two sources, the behavior and movements of identified individuals (not possible with radar) can be continuously monitored (not possible with satellite tags). In this study the radar detected 40% of the locations of vultures carrying GPS-PTT tags that were within 5 km of the radar. Most (75%) of the locations that were not detected were calculated to be above or below the radar’s antenna beam. Speed and direction values recorded by the GPS-PTT tags and the radar were poorly correlated because the vultures were soaring and circling, which produced rapid changes in both azimuth and ground speed of the targets. Nevertheless, our findings show that combining these two techniques can allow monitoring of species that are of conservation concern where it is otherwise difficult to follow identified individual birds.