Noise-dependent vocal plasticity in domestic fowl

Since acoustic communication is considerably constrained by environmental noise, some animals have evolved adaptations to counteract its masking effects. Humans and New World monkeys increase the duration of brief vocalizations (below a few hundred milliseconds) as the background noise level rises, a behaviour that increases the detection probability of signals in noise by temporal summation. We found that domestic fowl, Gallus gallus domesticus, exhibited the Lombard effect, that is, a regulation of vocal amplitude depending on the background noise level. This vocal mechanism for communication in noise is also found in mammals and other bird species. However, in contrast to primates, the chickens did not regulate the duration of their brief call syllables. This evidence for a lack of regulation of syllable duration may hint at limitations in the degrees of freedom for signal coding. Overall, 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.