Since acoustic communication is considerably constrained by environmental noise, some animals have evolved adaptations to counteract its masking effects. We found in psycho-acoustic experiments that domestic fowl (N=19) exhibited the Lombard effect, that is a regulation of vocal amplitude depending on the background noise level. This vocal mechanism for communication in noise has also been evolved in mammals and other bird species. Previous studies have shown that, in addition to the Lombard effect, humans and New World monkeys also increase the duration of brief vocalizations (below a few hundred milliseconds) as the background noise level rises, a behaviour which increases the detection probability of signals in noise by temporal summation. However, in contrast to primates, the chickens tested did not regulate the duration of their brief call syllables in relation to the level of masking background noise. This evidence for a lack of regulation of syllable duration suggests that this signal parameter cannot be regulated to maintain signal transfer in chicken because it is used to encode information or because this form of noise-induced vocal plasticity is perhaps an autapomorphy of mammals or even primates. Our findings indicate that the common problem of acoustic communication in noise has led to the evolution of a common solution, the Lombard effect, but also to special adaptations in different taxa.
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