Hearing in the swamp sparrow, Melospiza georgiana, and the song sparrow, Melospiza melodia

Abstract

Operant conditioning techniques and a psychophysical tracking procedure were used to measure thresholds for pure tones in two congeneric species of sparrows: swamp sparrows and song sparrows. Thresholds were measured both in quiet conditions and in the presence of white noise. The two species were similar in their gross pattern of auditory sensitivity with most sensitive thresholds in the frequency region of 1·0–8·0 kHz and poor hearing above and below this range. However, the best sensitivity occurred at 2 kHz for the song sparrows and at 4 kHz for the swamp sparrows. This pattern was also observed in song spectra of the two species. The songs of song sparrows had more power in lower frequencies than the songs of swamp sparrows. Masked auditory thresholds for both species were very similar, showing a generally increasing signal-to-noise ratio with increasing frequency. The similarity between swamp and song sparrows in these measures of basic auditory sensitivity suggests that the primary mechanisms underlying selective vocal learning in these sparrows probably reside at higher levels than the peripheral auditory sensitivities.