Vocal plasticity in mallards: multiple signal changes in noise and the evolution of the Lombard effect in birds

Abstract

Signal plasticity is a building block of complex animal communication systems. A particular form of signal plasticity is the Lombard effect, in which a signaler increases its vocal amplitude in response to an increase in the background noise. The Lombard effect is a basic mechanism for communication in noise that is well-studied in human speech and which has also been reported in other mammals and several bird species. Sometimes, but not always, the Lombard effect is accompanied by additional changes in signal parameters. However, the evolution of the Lombard effect and related vocal adjustments in birds are still unclear because so far only three major avian clades have been studied. We report the first evidence for the Lombard effect in an anseriform bird, the mallard Anas platyrhynchos. In association with the Lombard effect, the fifteen ducklings in our experiment also increased the peak frequency of their calls in noise. However, they did not change the duration of call syllables or their call rates as has been found in other bird species. Our findings support the notion that all extant birds use the Lombard effect to solve the common problem of maintaining communication in noise, i.e. it is an ancestral trait shared among all living avian taxa, which means that it has evolved more than 70 million yr ago. At the same time, our data suggest that parameter changes associated with the Lombard effect follow more complex patterns, with marked differences between taxa, some of which might be related to proximate constraints.

Influence of Anthropogenic Sounds on Insect, Anuran and Bird Acoustic Signals: A Meta-Analysis

“…Our results also suggest that the call amplitude increases in the presence of anthropogenic noise. Similar results have been shown in the literature for biotic noise, where studies have reported that the Lombard effect is a mechanism widely used by birds to avoid sound masking (Lampe et al, 2010;Zollinger and Brumm, 2011;Dorado-Correa et al, 2018;Singh et al, 2019). Zollinger and Brumm (2015) showed that changes in amplitude can have several costs for birds, for example, affecting sexual selection, defense of territory, condition and energy.…”

Signal-specific amplitude adjustment to noise in common bottlenose dolphins (Tursiops truncatus)

“…In humans, the magnitude of the Lombard response has been shown to vary according to experimental design, but increases in vocal amplitude generally range from 0.05 to 0.4 dB per 1 dB increase in noise level (Table 1; Garnier et al, 2010;Hotchkin and Parks, 2013). A similar Lombard response magnitude in the range of 0.2 to 0.8 dB per 1 dB increase in noise level has been demonstrated for other primates (Brumm et al, 2004;Egnor and Hauser, 2006) as well as bats (Tressler and Smotherman, 2009) and several different bird taxa (Brumm and Todt, 2002;Cynx et al, 1998;Dorado-Correa et al, 2018). Thus, many highly vocal terrestrial animals display a Lombard response that helps to partially offset the reduction in active space, yet none of them fully compensate for increased ambient noise and, therefore, face a loss of active space during periods of increased noise.…”