Performance and accuracy evaluation of small satellite transmitters

Recent technological advances have resulted in small (30 g) satellite platform transmitter terminals (PTTs) that can be used to track animals with masses as little as 900-1,000 g. While larger PTTs (>80 g) often yield locations accurate to within hundreds of meters, the location accuracy of smaller PTTs has not been tested. We did these tests while using the PTTs to document migration routes and nonbreeding areas of American peregrine falcons (Falco peregrinus anatum). We PTT-tagged 42 female peregrines from 2 breeding areas (upper Yukon River in eastcentral Alaska and Lake Powell on the Colorado Plateau in southern Utah and northern Arizona) late in the breeding seasons of 1993-95. Only 2 of the PTTs failed prematurely (4.7% failure rate). Active PTTs (i.e., PTTs on live birds that eventually stopped transmitting due to battery exhaustion) averaged 280 transmission hours for 1993-94 (n = 3), 380 transmission hours for 1994-95 (n = 7), and 430 transmission hours for 1995-96 (n = 15). Using an estimate of maximum ground speed of peregrines (104 km/hr) based on empirical observations and aerodynamic calculations, we determined that 4.48% of all locations provided to us by Argos (n = 2,323) were biologically implausible. We also received many poor-quality locations (68% of records were in Argos location classes 0, A, and B) typical of small, relatively underpowered PTTs. To estimate location accuracy of these poor-quality locations, we compared Argos-estimated locations with known locations of 11 rock doves (Columba livia) tagged with PTTs. The location types with the highest precision averaged 4 km from the true location, while the location types with the lowest precision averaged 35 km from the true location. These results indicate the PTT locations were sufficient to document animal movements over broad spatial scales such as identifying migration routes and nonbreeding areas of birds. This technology is more efficient and less biased than the current approaches used to obtain this information (mark-resighting of banded animals or standard radiotelemetry techniques). However, the PTTs currently available are not suitable when position accuracy <35 km is needed.