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.

Introductory gestures before songbird vocal displays are shaped by learning and biological predispositions

“…We chose to examine undirected songs because they provide a more controlled condition for quantifying IN number and structure. For example, INs before directed songs are influenced by distance from the female [36] and the quality of the stimulus [37]. In addition, the initial, softer INs can be lost in the increased background noise, typically associated with directed songs because of the movement of both birds and female vocalizations.…”