Dynamic biosonar adjustment strategies in deep-diving Risso's dolphins driven partly by prey evasion

Area of Science:

• Marine Biology
• Bioacoustics
• Animal Behavior

Background:

• Toothed whales use biosonar for foraging, with different species exhibiting varied click adjustment strategies.
• Shallow-diving delphinids, phocoenids, and iniids gradually adjust biosonar parameters during prey approach.
• Deep-diving whales like sperm and beaked whales maintain stable biosonar parameters before a rapid switch to a foraging buzz.

Purpose of the Study:

• To investigate whether deep-diving delphinids, specifically Risso's dolphins (Grampus griseus), share the rapid biosonar adjustment strategy of other deep-diving whales.
• To analyze biosonar adjustments of Risso's dolphins during prey capture attempts in their natural deep-water habitat.

Main Methods:

• Analysis of inter-click interval and apparent output level from sound recording tags attached to Risso's dolphins.
• Quantification of in situ sensory adjustments during prey capture attempts.

Main Results:

• Risso's dolphins did not follow the typical (20logR) biosonar adjustment patterns observed in shallow-water species.
• They maintained stable repetition rates and output levels until initiating the foraging buzz.
• A rapid transition to the foraging buzz was observed in most prey approaches, similar to beaked whales.
• In 19% of prey approaches, characterized by higher speeds and specific acceleration, Risso's dolphins employed a more gradual biosonar adjustment.

Conclusions:

• Deep-diving Risso's dolphins utilize a stable biosonar strategy, likely for maintaining a long-range acoustic scene in multi-target environments.
• This strategy appears common among deep-diving toothed whales.
• The capture of evasive prey may necessitate a more gradual shift between multi-target echolocation and single-target tracking.