Homing pigeons can detect small shifts in sound frequency at 1, 2, 5, 10, and 20 Hz. Their thresholds range from a 1% shift at 20 Hz to a 7% shift at 1 Hz. The frequency shifts used were designed to simulate the natural Doppler shifts resulting from changes in flight path. Their ability was sufficiently sensitive to make it feasible that natural Doppler shifts can be detected. Further tests indicated that the birds can perform true frequency discrimination when all subjective amplitude cues are removed. These laboratory tests are further steps in a series designed to find out if homing pigeons use infrasounds as cues for orientation and navigation.
We thank our colleague, Prof. Wm. T. Keeton for his encouragement and support and John Willis for technical assistance. This research was supported by Grants No. BNS 77-24903 and BNS 78-13016 from the National Science Foundation, and by Hatch funds.
Present address: Department of Biology, University of Pittsburgh, and Section of Birds, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania 15260, USA