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2 bioacoustics papers - J Exp Biol

To: Bioacoustics <>
Subject: 2 bioacoustics papers - J Exp Biol
From: Alan McElligott <>
Date: Thu, 14 Dec 2006 18:05:00 +0000 (GMT)
Echolocation signals of wild harbour porpoises, Phocoena phocoena
Anne Villadsgaard, Magnus Wahlberg and Jakob Tougaard
Journal of Experimental Biology 210, 56-64 (2007)

Field recordings of harbour porpoises (Phocoena phocoena) were made in
the inner Danish waters with a vertical array of three or four
hydrophones. The back-calculated source level ranged from 178 to 205
dB re 1 uPa pp @ 1 m with a mean source level of 191 dB re 1 uPa pp @
1 m. The maximum source level was more than 30 dB above what has been
measured from captive animals, while the spectral and temporal
properties were comparable. Calculations based on the sonar equation
indicate that harbour porpoises, using these high click intensities,
should be capable of detecting fish and nets and should be detectable
by porpoise detectors over significantly larger distances than had
previously been assumed. Harbour porpoises in this study preferred a
relatively constant inter-click interval of about 60 ms, but intervals
up to 200 ms and down to 30 ms were also recorded.

Key words: Odontoceti, Phocoena phocoena, biosonar, target detection,
click, source level, inter-click interval, bycatch, acoustic

Danilo Russo, Gareth Jones and Raphael Arlettaz
Journal of Experimental Biology 210, 166-176 (2007)

The two sibling mouse-eared bats, Myotis myotis and M. blythii, cope
with similar orientation tasks, but separate their trophic niche by
hunting in species-specific foraging microhabitats. Previous work has
shown that both species rely largely on passive listening to detect
and glean prey from substrates, and studies on other bat species have
suggested that echolocation is `switched off' during passive
listening. We tested the hypothesis that mouse-eared bats continuously
emit echolocation calls while approaching prey. Echolocation may be
needed for orientation while simultaneously listening for
prey. Because these sibling species forage in different microhabitats
and eat different prey, we also compared their echolocation behaviour
and related it to their ecology. Both species used echolocation
throughout prey approach, corroborating a functional role for
echolocation during gleaning. Captive bats of both species emitted
similar orientation calls, and pulse rate increased during prey
approach. Between the search to approach phases, call amplitude showed
a sudden, dramatic drop and bats adopted `whispering echolocation' by
emitting weak calls. Whispering echolocation may reduce the risks of
masking prey-generated sounds during passive listening, the
mouse-eared bats' main detection tactic; it may also avoid alerting
ultrasound-sensitive prey. In several cases M. myotis emitted a loud
buzz made of 2-18 components when landing. We hypothesise that the
buzz, absent in M. blythii at least when gleaning from the same
substrate, is used to assess the distance from ground and refine the
landing manoeuvre. Our findings have implications for niche separation
between sibling species of echolocating bats, support a role for
echolocation during passive listening and suggest a functional role
for buzzes in landing control.

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