Echolocation by two foraging harbour porpoises (Phocoena phocoena)

Abstract

SUMMARYSynchronized video and high-frequency audio recordings of two trained harbour porpoises searching for and capturing live fish were used to study swimming and echolocation behaviour. One animal repeated the tasks blindfolded. A splash generated by the fish being thrown into the pool or -in controls -by a boat hook indicated prey and stimulated search behaviour. The echolocation sequences were divided into search and approach phases. In the search phase the porpoises displayed a clear range-locking behaviour on landmarks, indicated by a distance-dependent decrease in click interval. Only in trials with fish was the search phase followed by an approach phase. In the initial part of the approach phase the porpoises used a rather constant click interval of around 50 ms. The terminal part started with a sudden drop in click interval at distances around 2-4 m. Close to the prey the terminal part ended with a buzz, characterized by constant click intervals around 1.5 ms. The lag time in the search and the initial part of the approach phase seems to be long enough for the porpoise to process echo information before emitting the next click (pulse mode). However, we assume that during the buzz lag times are too short for pulse mode processing and that distance information is perceived as a 'pitch' with a 'frequency' corresponding to the inverse of the two-way transit time (pitch mode). The swimming speed of the animal was halved when it was blindfolded, while the click intervals hardly changed, resulting in more clicks emitted per metre swum.

Discrimination of fast click series produced by tagged Risso's dolphins (Grampus griseus) for echolocation or communication

“…Therefore, presuming that the end of the buzz coincides with prey capture, Grampus start buzzing when they are approximately one body length (∼3 m) from the target prey. This distance of one body length is consistent with the onset of the terminal phase of prey capture in all odontocetes studied (Miller et al, 1995;Akamatsu et al, 2005;Madsen et al, 2005;Aguilar Soto et al, 2008;Verfuss et al, 2009). The mean ICI of Grampus buzzes (3-4 ms) is shorter than that of larger odontocetes, such as Blainville's beaked whales (3-5 ms) and sperm whales (11 ms), consistent with an ICI scaled to the size of the animals, as suggested by Madsen and Surlykke (2013).…”

Support for the beam focusing hypothesis in the false killer whale

“…If there is a maximum curvature possible for the melon as a result of anatomical limitations, this would impose a minimum FR for the transmitted sonar waveform. Many odontocete species produce low-amplitude, high-repetition clicks (termed 'buzzes') when prey are within one body length (DeRuiter et al, 2009;Johnson et al, 2004;Verfuss et al, 2009;Wisniewska et al, 2014). These buzzes are distinctly different from the clicks made when prey are at greater distances, and their rapid production rate may eliminate any need for focusing.…”

Directional escape behavior in allis shad (Alosa alosa) exposed to ultrasonic clicks mimicking an approaching toothed whale

“…Another possible cue to the proximity of the predator is the rate at which a toothed whale is clicking (Astrup, 1999;Astrup and Møhl, 1997). Like echolocating bats, toothed whales produce echolocation clicks at a higher repetition rate when they approach their prey, and most prey capture attempts are terminated with a buzz phase during which the repetition rate is up to several hundred clicks per second (Miller et al, 1995;Madsen et al, 2002;Madsen et al, 2005;Deruiter et al, 2009;Verfuss et al, 2009). Thus, if ultrasound detection in Alosinae is used as a way to avoid predation from toothed whales, we hypothesize that Alosinae will exhibit negative phonotaxis, i.e.…”