Amplitude regulation of vocalizations in noise by a songbird, Taeniopygia guttata.

Bird vocalizations are produced under various noise conditions. It could therefore benefit birds to alter the amplitude of their signals as noise conditions change. We tested this by recording male and female zebra finches, Taeniopygia guttata, as they were subjected to various levels of white noise. Both sexes increased amplitude levels of vocalization in response to increased levels of noise. Similar results were obtained with humans (the 'Lombard effect'). The results are discussed in terms of the 'active space' of bird song and honest signalling. Copyright 1998 The Association for the Study of Animal Behaviour.