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

Ida M. Kragh, Katherine McHugh, Randall S. Wells, Laela S. Sayigh, Vincent M. Janik, Peter L. Tyack, Frants H. Jensen

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Anthropogenic underwater noise has increased over the past century, raising concern about the impact on cetaceans that rely on sound for communication, navigation and locating prey and predators. Many terrestrial animals increase the amplitude of their acoustic signals to partially compensate for the masking effect of noise (the Lombard response), but it has been suggested that cetaceans almost fully compensate with amplitude adjustments for increasing noise levels. Here, we used sound-recording DTAGs on pairs of free-ranging common bottlenose dolphins (Tursiops truncatus) to test (i) whether dolphins increase signal amplitude to compensate for increasing ambient noise and (ii) whether adjustments are identical for different signal types. We present evidence of a Lombard response in the range 0.1–0.3 dB per 1 dB increase in ambient noise, which is similar to that of terrestrial animals, but much lower than the response reported for other cetaceans. We found that signature whistles tended to be louder and with a lower degree of amplitude adjustment to noise compared with non-signature whistles, suggesting that signature whistles may be selected for higher output levels and may have a smaller scope for amplitude adjustment to noise. The consequence of the limited degree of vocal amplitude compensation is a loss of active space during periods of increased noise, with potential consequences for group cohesion, conspecific encounter rates and mate attraction.

Original languageEnglish (US)
Article numberjeb.216606
JournalJournal of Experimental Biology
Issue number23
StatePublished - 2019
Externally publishedYes


  • Anthropogenic noise
  • Cetacean
  • Communication
  • Lombard response
  • Masking
  • Signature whistle

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science


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