Distance-dependent changes in courtship song amplitude reflect song state changes

ABSTRACT Many animals increase the amplitude of their vocalizations as distance from a receiver increases. However, behavioral mechanisms underlying this increase remain unclear. Here, we addressed this using head-attached microphones to accurately record song amplitude in male zebra finches while presenting a female at difference distances. We show that individual courtship song syllables either increased (5/13) or decreased their amplitude (4/13) as distance from the female increased. Both increases and decreases were part of more general acoustic changes that resulted in properties more similar to those of “undirected” songs typically produced in the absence of a female. Increasing distance also reduced female responses to songs and absence of female responses reduced courtship song amplitude and number of songs per bout. These data suggest a simple behavioral mechanism where distance-dependent song amplitude changes reflect song state changes. Such state changes may be a general mechanism underlying distance-dependent amplitude changes in other organisms.