Michael Ladegaard


  • My research focuses on how range-dependent biosonar adjustments are actively used by toothed whales during target approaches, and on how source parameters may depend on the environment and differ between species.

Toothed whales forage on individual prey in a wide range of habitats often characterised by poor lighting conditions. Though vision is used when possible, toothed whales engaged in finding, approaching, and capturing prey rely heavily on their ability to echolocate which encompasses production of powerful high-frequency clicks and detection of low-amplitude echoes returning from ensonified targets. During the phases leading up to a prey interception, toothed whales dynamically adjust the source parameters of their biosonar clicks which may involve changes such as decreasing source levels, increasing click rates, and increasing biosonar beam widths as the prey gets closer.

Over the last five years I have worked on projects including:

(1) Characterisation of the biosonar of wild Amazon river dolphins (a.k.a botos), using a linear seven-hydrophone array for localising echolocating animals, to test the hypothesis that botos make use of a directional, short-range biosonar compared to similar-sized marine dolphins.

(2) Biosonar adjustments of wild botos during prey approaches in a study using (i) a star-shaped hydrophone array for sound source localisation and (ii) a dead fish instrumented with a hydrophone for recording received levels at the prey. In that study we showed that botos click at higher rates than similar-sized toothed whales generally do at comparable target ranges, but that the terminal phase of prey capture involves buzzing (or extremely high-rate clicking) at click rates 3-4 times lower than expected, which may be an adaptation to echolocation in cluttered and acoustically complex environments.

(3) Long-range echolocation adjustments in trained bottlenose dolphins instrumented with sound-and-movement tags during target approaches over ranges up to ~400 m. We show that discrete click packets are produced when target ranges exceed ~100 m and that short-range echolocation may involve interclick intervals shorter than the acoustic two-way travel time to the target, which is in contrast to most observations on toothed whale clicking rates.

(4) Harbour porpoise biosonar adjustments in two highly different environments (a semi-natural harbour basin and a shallow-water holding pool) when solving an identical task of actively approaching the same target over the same ranges.

(5) Context-dependent biosonar adjustments in porpoises approaching the same target in different environmental settings to identify if the factor of environment co-modulates the range-dependent adjustments made.

(6) Range-dependent output adjustments in porpoises approaching different sized targets under different noise conditions to investigate the hypothesis that source levels are adjusted to keep echo levels rougly constant for different-sized targets and ranges.

I defended my PhD titled “Echolocation in small cetaceans” in August 2017. Since then I have worked as a postdoc at Aarhus University on biosonar, underwater noise effects, and long-term passive acoustic monitoring.

Contact information:

mail  michael.ladegaard@bio.au.dk


researchgate  ResearchGate

website  Profile page at Aarhus University 

Star-shaped hydrophone array (Reson TC4013) used for recording Amazon river dolphins in the Mamirauá Sustainable Development Reserve, Amazon, Brazil. Photo: Michael Ladegaard