Spatial orientation in echolocating harbour porpoises (Phocoena phocoena)

Abstract

SUMMARY Studies concerning the echolocation behaviour of odontocetes focus mainly on target detection and discrimination, either in stationary animals or in animals approaching a specific target. We present the first data on the use of echolocation for spatial orientation or navigation. Synchronised video and high-frequency recordings were made of two harbour porpoises trained to swim from one position to another across an outdoor pool in order to correlate swimming and echolocation behaviour. Both porpoises showed a clear range-locking behaviour on specific positions near the end of the pool, as indicated by a decrease in click interval with decreasing distance. The decrease in click interval followed the two-way-transit time, which is the time interval between the outgoing click and the received echo from the focal object. This suggests that the porpoises used focal objects as landmarks. The lag time, defined as the time between the arrival of an echo from a landmark and the emission of the next click, was task specific. The lag time was longer for difficult tasks (26–36 ms) and shorter for simpler tasks(14–19 ms), with some individual differences between the two animals. Our results suggest that echolocation by odontocetes is used not only for target detection, localisation and classification but also for spatial orientation.

Comparison of echolocation behaviour between coastal and riverine porpoises

“…The inter-pulse interval depends more on the size of the swimming environment rather than species differences (Akamatsu et al, 1998). This suggests that the tagged harbor porpoise in the present study scanned various distances, while the captive porpoise might only have used its sonar ranging to cover the distance of the enclosure (Verfuss et al, 2005).…”

“…The lag time (signal processing time of an echo in biological sonar) of captive harbor porpoises is 26-36 ms for difficult tasks and 14-19 ms for simpler tasks with individual differences (Verfuss et al, 2005). Here we use a 20 ms lag time for both species to standardise the comparison.…”

“…Behavioural data, such as dive depth and times, and potential target distance, can be obtained by using acoustic tags supplemented with additional data acquisition devices. For some captive odontocetes there is a linear correlation between inter-pulse interval and target range as shown by the bottlenose dolphin, Tursiops truncatus (Au, 1993), false killer whale, Pseudorca crassidens (Thomas and Turl, 1990), and the harbor porpoise (Verfuss et al, 2005). The inter-pulse interval is longer than the two-way sound travel time to and back from the target (Morozov et al, 1972).…”

“…6). Verfuss et al (2005) (Akamatsu et al, 2005a). showed that captive harbor porpoises adjusted the click intervals to the target range during most of the approach. In the later part of the approach phase of the present study, the inter-pulse interval changed by approximately 5.8 ms during 2.6 s indicating an estimated change in sonar range of 4.4 m. If the porpoise locked its sonar on a target at this time, the approaching speed would be 1:7 m s À1 .…”

A Neurological Comparative Study of the Harp Seal (Pagophilus groenlandicus) and Harbor Porpoise (Phocoena phocoena) Brain

“…Along with these morphological changes are other features of their lifestyle, including highly developed auditory abilities such as echolocation. Odontoceti, such as the harbor porpoise (Phocoena phocoena), makes use of echolocation as its primary sensory system when navigating and foraging (Verfub et al, 2005), though it has also been suggested to use its vision while foraging (Teilmann et al, 2007).…”