Diel Variation in Echolocation Behavior of Wild Harbor Porpoises

Abstract

The echolocation rate and behavior of wild harbor porpoises were studied using a harbor porpoise click detector (POD) deployed close to the bottom at 40 m depth in Scottish waters, UK, April—June 2001. Echolocation variables were compared among four diel phases; morning, day, evening, and night. The echolocation encounter rate, the minimum interclick interval per train, and the proportion of echolocation click trains with a minimum interclick interval below 10 msec were all significantly higher at night than during the day. The variation in echolocation rate implies that porpoises increased their echolocation rate and/or visited the depth of the POD more often at night than during the day. Further, the changes in minimum interclick interval per train suggest that they used their echolocation for foraging or investigating objects at a close range to a higher extent, and acoustically explored the environment at greater distances at night than during the day.

Using Static Acoustic Monitoring to Describe Echolocation Behaviour of Heaviside’s Dolphins (Cephalorhynchus heavisidii) in Namibia

“…Click rates were comparable with those reported for Heaviside's dolphins (ICIs of 2 to 113 ms; Morisaka et al, 2011) and harbour porpoises (MICIs up to 120 ms; Carlström, 2005). It is possible that the very few click trains with mean ICI values above 167 ms represent false positive detections.…”

“…Click trains from Heaviside's dolphins at Pelican Point displayed higher mean ICIs during the daytime than at night, indicating that clicks were produced at faster rates during the night. Click trains with lower ICI values have been associated with the investigation of objects at close range and feeding (Akamatsu et al, 2005;Carlström, 2005;Verfuβ et al, 2009). In a study of harbour porpoise click behaviour in Scotland, Carlström (2005) reported a peak in mean MICI per train at night and suggested that this slower click rate indicated that porpoises used their echolocation to explore their surroundings at greater distances during the night than in the day.…”

“…In the terminal phase of the approach of harbour porpoises to prey items, the ICI is first reduced from about 50 ms to intervals below 10 ms and is then kept short and constant at values between 1.4 and 1.6 ms (Verfuβ et al, 2009). In order to investigate diel patterns in the proportion of "fast" click trains from harbour porpoises, Carlström (2005) chose 10 ms as the value below which to define such trains, based on the shapes of the frequency distributions of MICI and on ICI of captive animals, which were recorded during different behaviours from other studies (Carlström, 2005, and references therein). For this study, we therefore chose to use ICI values below 10 ms as a possible indicator of feeding behaviour or target-locking.…”

“…To reduce the likelihood of this occurring, we further filtered our data by excluding time periods in which bottlenose dolphin-like clicks (50 to 70 kHz) were recorded. For data calculated per minute, any whole minutes of data in which bottlenose dolphin-like clicks were recorded, as well as the minute before and after that time, were (Carlström, 2005;Todd et al, 2009). Feeding-buzz ratio (FBR) has previously been used as an indicator of potential feeding behaviour for odontocetes (Todd et al, 2009).…”

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

“…Another possible explanation of the lack of difference in cell density could be that they rely more on vision than first assumed (Teilmann et al, 2007). This is supported by the fact that harbor porpoises have been found to click more during the nighttime (Otani et al, 1998;Carlstrom, 2005).…”