Acoustic communication in noise: regulation of call characteristics in a New World monkey

Abstract

This study on common marmosets Callithrix jacchus is the first to examine noise-dependent mechanisms of vocal plasticity in a New World monkey. Since acoustic communication can be considerably impaired by environmental noise, some animals have evolved adaptations to counteract its masking effects. The studied marmosets increased the sound level of their spontaneous calls in response to increased levels of white noise broadcast to them. Possibly, such noise-dependent adjustment of vocal amplitude serves to maintain a specific signal-to-noise ratio that is favourable for signal production. Concurrently, the adjustment of vocal amplitude can maintain a given active space for communication. In contrast to some bird species, no noiseinduced increase in the number of syllables per call series could be found, showing that an increased serial redundancy of vocal signals was not used to communicate under noisy conditions. Finally, we examined a possible noise-dependent prolongation of vocal signals. This approach was guided by the findings of perceptional studies, which suggest an increased detection probability of prolonged signals in noise by temporal summation. Marmosets indeed increased the duration of their call syllables along with increasing background noise levels. This is the first evidence of such mechanism of vocal plasticity in an animal communication system.

Changes in bottlenose dolphin whistle parameters related to vessel presence, surface behaviour and group composition

“…Prolonging call duration is another mechanism whereby animals may increase detection probability in elevated noise conditions (Brumm, Voss, Köllmer, & Todt, 2004). Several delphinid species, including one population of bottlenose dolphins, have been found to increase call duration in relation to boat presence (Foote et al, 2004;Lesage et al, 1999;May-Collado & Wartzok, 2008), while others have not (Buckstaff, 2004;Luís et al, 2014).…”

Ambient noise induces independent shifts in call frequency and amplitude within the Lombard effect in echolocating bats

“…Vocal changes associated with the Lombard effect have rarely been analyzed in animal species. So far, noisedependent changes in call frequency have been observed in birds (8,11,22), and changes in call duration in birds and monkeys (8,12).Most animal studies, however, have focused on noise-dependent changes in call amplitude and do not examine other possible vocal changes (2-5, 7, 9, 10, 15-17). It is therefore still largely unknown how the adaptive changes in call amplitude relate to frequency shifts or call elongation and how the underlying mechanisms are linked.…”

“…Vocal changes associated with the Lombard effect have rarely been analyzed in animal species. So far, noisedependent changes in call frequency have been observed in birds (8,11,22), and changes in call duration in birds and monkeys (8,12).…”

“…One of the most efficient mechanisms is the socalled Lombard effect, i.e., the involuntary rise in call amplitude in response to masking ambient noise (1). This effect was first described in human communication a century ago (2) and has since been found in several species of birds (3)(4)(5)(6)(7)(8)(9)(10)(11) and various mammals (12)(13)(14)(15)(16)(17), including bats (18). In human speech, several vocal changes, such as a rise in fundamental frequency (19) or lengthening in word duration (20), are often accompanied with the Lombard effect; combined, these changes are referred to as Lombard speech (21).…”

Convergence and divergence in Diana monkey vocalizations

“…Temporary acoustic modification has been documented in reaction to ambient noise, social isolation and habitat [11][12][13]. Acoustic convergence has been documented in terms of callers matching some of each others' acoustic features during vocal exchanges or as part of social bonding [14,15].…”