ABS 2022
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Relationship between frequency and amplitude in bird vocalizations
Joao C. T. Menezes, Jeffrey Podos. University of Massachusetts Amherst, Amherst, MA, United States

Sounds are the main channel of long-range communication in birds. In general, individuals may be expected to benefit from vocalizing at higher amplitudes because amplitude increases a sound's range and therefore the potential number of intended receivers. Another way to maximize a sound’s range is to vocalize at lower frequencies, which are less susceptible to heat losses. However, biophysical models of avian sound production predict that amplitude and frequency should be positively coupled, which could limit birds’ vocal spatial range. Here, we quantified relationships between vocal amplitude and frequency of multiple species to test whether their association is negative (as predicted if birds managed to maximize sound range) or positive (as predicted by biophysical constraints). For most species, we found frequency to correlate positively with amplitude, indicating an overarching role for biophysical constraints on frequency-by-amplitude relationships. This trade-off may shape communication systems by delimiting optimal combinations of amplitude and frequency that maximize a vocalization’s range.