e. three detections in six antenna revolutions) to classify a set of detections as a Track. Birds that were near the edge of the antenna pattern or near the sensitivity threshold often produced an erratic pattern of intermittent detections but not a continuous Track (Fig.
1). Such patterns were classified as probable confirmations but no information on speed and heading could be determined. To determine whether a bird was within the radar’s beam pattern we compared its altitude from the PTT tag with that calculated for the radar’s upper and lower pattern boundaries. The PTT tag uses GPS technology to determine altitude, which has an accuracy uncertainty that depends on the number of satellites in view and their locations in the sky. When learn more comparing the PTT altitude with the radar’s Wnt inhibitor altitude value, we used an uncertainty of ±25 m for the PTT altitude value. This is slightly greater than the 18 m listed by the manufacturer (Microwave Telemetry Inc.) for times with maximum satellite coverage and better reflects field conditions. The radar antenna we used produces a circular cross-section beam that is 4° diameter. We calculated the upper and lower edges of the antenna’s coverage based on the
distance of each bird from the radar and allowed for a ±0.5° beam-width uncertainty for the antenna. The radar’s vertical beam width uncertainty is based on several potential causative factors: (1) it was impossible to determine, with the equipment available, whether the antenna was level to within <0.5°; (2) although the calculated beam at 3 dB down is 4° across, the antenna pattern is not a sharp cut-off; (3) imperfections in the antenna could result in a wider beam pattern; (4) the measurement of the antenna’s elevation angle might not be precise enough to be accurate to within <0.5°. One hundred and eighty-two GPS-PTT locations were within the 5 km digitization range of the radar. Two reports were excluded because the radar was not operating when the reports were taken. Of the remaining 180 reports, 13 Thiamet G were from three black vultures and 167 were from two turkey vultures. Of the 180 PTT locations within 5 km of the radar, 70 positions were reported by
the radar software as Tracks (n=48; Fig. 1) or as sporadic detections but not consistent enough for the software to compute a Track (n=22; Fig. 1). Twenty-eight additional locations were computed to be within the radar beam but were not detected by the radar (Fig. 2a). Of the 70 locations confirmed by radar detections, 22 were calculated to be above or below the antenna beam by a mean of 72 m (±11.6 se, range 1–181 m). Almost three-fourths (15 of 22 targets) of those were within 80 m vertically of the calculated coverage of the radar beam. Beyond 4.5 km only two birds were detected by radar, and only intermittently (detections too inconsistent to produce a track). Beyond 4.5 km two additional birds were calculated to be within the beam but were not detected.