Dolphin echolocation behaviour during active long-range target detection

Activity: Talk or presentation typesLecture and oral contribution

See relations at Aarhus University

Michael Ladegaard - Lecturer

Short-range (< ~100 m) experiments on echolocating dolphins suggest that source levels (SL) and interclick intervals (ICI) are adjusted with target range in a stereotyped manner, but little is known about how free-moving dolphins adjust click emissions while approaching a target from long range. Here we trained two bottlenose dolphins (Tursiops truncatus) instrumented with a Dtag3 to approach a known target from ranges up to 450 m and used the time-of-arrival differences between clicks recorded on the dolphins and target to estimate target range. The dolphins dynamically adjusted ICI and SL at target ranges of less than ~100 m. For target ranges exceeding this apparent threshold, the dolphins commonly switched to click packet production. The packet echolocation mode is therefore not an artefact of studying animals that are not exposed to the acoustic flow created when traversing the environment to the target. We further demonstrate that not only do dolphins operate in packet mode at long ranges where infrequent and potentially low-accuracy range estimations are less critical, but also that short-range echolocation down to 25-30 m from the target can involve ICIs shorter than the two-way travel time (TWTT). This echolocation behaviour possibly leads to range ambiguity problems and can lead to varying perceived echo levels even in situations where click SL and target range does not change. This occur due to differential forward masking at echo return times because echo time delays relative to the most recent click event does not correspond to target range, as is usually the case when ICI exceed the TWTT, but to clicking rate. That the ICI of toothed whale echolocation clicks always exceeds the TWTT to the target appears to be a general rule, but we encourage future studies to explore range ambiguity resolving capabilities in biosonar systems.
9 Mar 201810 Mar 2018

Event (Conference)

TitleDansk Havpattedyrsymposium
Date09/03/201810/03/2018
LocationDanhostel Hillerød
CityHillerød
CountryDenmark
Degree of recognitionNational event

    Keywords

  • Biosonar, Echolocation, bioacoustics, Dolphin, Tursiops

Publications

ID: 176505663