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| Sound produced | yes, active sound production |
| Type of sound produced | barks, grunts, escape sounds |
| Sound production organ | pneumatic duct & swim bladder |
| Sound mechanism | not known, but probably produced by discharge of compressed gas through pneumatic duct, amplified by swim bladder |
| Behavioural context | spontaneous frequent sound production, nocturnal, associated with onset of foraging activities (chasing prey). |
| Reference | Tiepelt, H., 2005 |
| Remark | outdoor recording (freshwater lake). Sounds were produced by single specimen. Sound sequence, consisting of 7 double sounds and 1 single sound, well timed and rhythmical. Last sound showed max. acoustical energy & upward jump in frequency. |