| Summary: | The harbor porpoise ( Phocoena phocoena ) is a small toothed whale living mostly in coastal waters. There are large, but unknown, numbers in the inner Danish waters. Four are in captivity at Fjord & Bælt, Kerteminde, Denmark, one of which was born here in 2007. Harbor porpoises use their ultrasonic clicks as biosonar for orientation and detection of prey (mostly smaller pelagic and bottom dwelling fish), and for communication. For studying wild animals, hydrophone arrays [Villadsgaard et al. J.Exp.Biol. 210 (2007)] and acoustic (time/depth) tags [Akamatsu et al. Deep Sea Research II 54 (2007)] have been used. For studying captive animals, arrays and video techniques [Verfuß et al. J.Exp.Biol. 208 (2005)] as well as miniature acoustic-behavioral tags [Deruiter et al. JASA 123 (2008)] have been used. While searching for prey, harbor porpoises use clicks at long intervals (>50 ms) that progressively decrease when closing on a landmark. The source levels of captive animals reduce by about half for each halving of the distance to the target. After detecting the prey, the click interval first stabilizes at about 50 ms and then becomes progressively shorter while approaching the prey. The sequence ends in a terminal, high repetition rate buzz (>600 clicks/s) just before capturing the prey (a video will be shown). The temporal sequence resembles that of beaked whales and bats
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