Effects of vocal learning, phonetics and inheritance on song amplitude in zebra finches

Birdsong is an important model in the study of evolutionary processes. Vocal amplitude, a song trait that has received little attention to date, varies considerably between individuals, and this variation is important in both female choice and male-male competition. To understand the function of a trait, it is often insightful to look at its origin and ontogeny. Like human speech, birdsong is a learned behaviour, and song amplitude may be adopted from the tutor during vocal ontogeny. However, vocal amplitude may also be bound to song phonetics owing to production constraints. We addressed these ideas with song-learning experiments in the zebra finch, Taeniopygia guttata, a widely used species in vocal-learning studies. The songs of young males were compared to the songs of their genetic fathers and to those of their tutors. We found that the amplitude of tutee song elements was strongly related to the tutor element amplitude, indicating that amplitude is affected by song learning. Therefore, song amplitude could be learned and/or be related to the acoustic structure of song elements owing to production constraints. In line with the latter hypothesis, element amplitude varied with structural element properties (duration and pitch). Mean element amplitude of the genetic father was not related to tutee element amplitude and our heritability estimates of song amplitude were not significant (but statistical power was low). Our findings indicate that the ontogenetic development of adult song amplitude is based on interplay between vocal production learning and physiological constraints. (C) 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.