Background
Anthropogenic (human-made) noise is recognized as a marine pollutant by the European Union. One of its most persistent effects on marine mammals is auditory masking – a phenomenon that occurs when noise overlaps with communication signals in both time & frequency, making it harder for animals to hear one another.
Cetaceans, such as whales and dolphins, rely heavily on sound for social interactions, navigation, and foraging. Fortunately, they possess some ability to cope with masking. They may shift the frequency of their calls, increase the rate at which they call, or raise their call amplitude – a behavior known as the Lombard response.
The Lombard response has been extensively documented in both terrestrial and marine mammals. Early studies suggested that cetaceans could nearly fully compensate for increased background noise, matching each 1 dB increase in noise with a 1 dB increase in call amplitude. However, advances in data collection and acoustic analysis have led to a revised view: recent research suggests that many species exhibit only a partial Lombard response, meaning their ability to compensate is more limited than previously thought.
Aims
- Quantify the Lombard response: assess how much long-finned pilot whales increase their call amplitude in response to rising ambient noise levels.
- Compare responses across call types and contexts: investigate whether the degree of vocal compensation varies between different call types and dive phases (e.g., surface, shallow dive, descent, ascent).
- Explore depth-related vocal adjustments: examine how call output level changes with increasing depth, and whether depth plays a role in shaping vocal behavior.