SONG DEGRADATION AND ESTIMATION OF ACOUSTIC DISTANCE IN BLACK-CAPPED CHICKADEES (PARUS ATRICAPILLUS)

Black-capped Chickadees (Parus atricapillus) sing a two-note song termed fee bee. Frequency descends within the fee note and between the fee and bee notes. Within-song frequency ratios are highly invariant, while among songs, absolute frequency is variable. We conducted sound-transmission studies to analyze how Black-capped Chickadee songs degrade in different native habitats. We then subjected colour-banded territorial males to playback of undegraded and degraded songs to see if they could estimate the distance to a conspecific singer by means of degradation cues. In transmission studies conducted in an open field and a dense deciduous forest, significant effects of reverberation and amplitude modulation were measured for songs at three different frequencies. A new technique, cross-correlation of song spectrograms, allowed for a measure of holistic song degradation, which varied significantly over distance in open versus forested habitat. Polynomial regressions for the effects of reverberation, amplitude...

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