Bat Echolocation Researc h - Bat Conservation International

species (Thies et al. 1998). Before these works were published,
the short, low intensity, multi-harmonic echolocation
calls of plant-visiting bats did not offer much
promise in the detection or evaluation of food. The same
absence of the lack of a clear role for echolocation
applies to the blood-feeding vampire bats.
The signals that an individual uses for echolocation (to
collect information about its surroundings) are also available
to others. Playback experiments have demonstrated
how echolocation calls can serve a communication function
in a variety of species such as Myotis lucifugus (Barclay
1982), Euderma maculatum (Leonard and Fenton 1984), and
Lasiurus borealis (Balcombe and Fenton 1988). There is evidence
that in Otomops martiensseni, calls originally associated
with echolocation may actually serve more for communication
(MBF unpublished observations).
A bat’s communication repertoire typically includes
other signals. Acoustic signals dedicated to communication
are longer in duration than echolocation calls (and
therefore of minimal value in echolocation because of
pulse-echo overlap). Some are individual-specific and
serve in food location and group maintenance (Boughman
and Wilkinson 1998), while others are interspersed
with echolocation calls and associated with mating (Barlow
and Jones 1997). Bats appear to simultaneously use
some vocalizations for echolocation and others for
social purposes, placing interesting demands on their
auditory systems because it necessitates simultaneous
processing of different kinds of auditory information. In
many species, communication also involves the use of
olfactory signals (Bouchard 2001). People whose first
language is English should make a special effort to keep
abreast of data published in other languages, particularly
in the area of echolocation and social behavior (e.g.,
Limpens et al. 2001).
THINGS FOR WHICH ECHOLOCATION
PROBABLY DOES NOT WORK
The short effective range of echolocation appears to
preclude using this mode of orientation in navigation
and other long-distance (> 20 m) perceptions. For example,
a Macrotus californicus would first see a tree-sized
object at over 1 km and a June beetle-sized insect at18
m, while an Eptesicus fuscus would only see the June beetle
at 1 m and the tree at about 300 m (Bell and Fenton
1986). Phyllostomus hastatus deprived of vision appear to
use some combination of spatial memory and echolocation
to orient themselves and find “home” (Williams et
al. 1966). Eptesicus fuscus use the glow of sunset in general
orientation (Buchler and Childs 1982). We do not
know what cues bats that make long distance migrations
use, but certainly vision offers more promise in these situations
than echolocation because of effective range.
Verboom et al. (1999) have demonstrated how Myotis
dasycneme used echolocation to collect data about their
general surroundings.
Low-intensity calls dominated by higher frequencies
should translate into a very short effective range, probably
substantially less than the 5-m range for 19-mm
diameter targets demonstrated for Eptesicus fuscus (Kick
1982). Mind you, I would also have said this about flower-visiting
bats prior to the publication of reports by von
Helversen and von Helversen (1999) and von Helversen
et al. (2003) or fruit-eating bats before reports from
Thies et al. (1998) and Kalko and Condon (1998).
ECHOLOCATION AND OUR VIEW OF BATS
Curiosity about echolocation and the appearance of
affordable equipment for studying it have meant that
research on bat sounds has dominated our perception of
these animals. From the outset, however, Griffin (1958)
and others (e.g., Suthers 1970) repeatedly reminded us
that bats can see and, like other mammals must use a
range of channels (visual, olfactory, acoustic, tactile) in
communication (Altringham and Fenton 2003). Perhaps
the most interesting frontier for bat biologists is the
means by which bats integrate the information they collect
through the various senses.
Echolocation has changed our view about the diversity
of bats. Differences in echolocation calls backed up
by molecular data led Barrett et al. (1997) to ascertain
that bats called Pipistrellus pipistrellus really were two
species. We can expect other such examples to emerge
as we increase our databases documenting variation in
echolocation calls (Obrist 1995).
RECOMMENDED READING
To appreciate the entanglement of the way we see
bats and echolocation, I strongly recommend that you
read two classic books, Glover M. Allen’s BATS (1939)
and Donald R. Griffin’s Listening in the Dark (1958). The
first book will take you back to our view of bats, their
biology and natural history, in the days before echolocation.
The second will change your view of bats by
making echolocation front and center. Then read André
Brosset’s classic La Biologie des Chiroptères (1966) to see how
echolocation begins to intertwine with our view of the
biology and natural history of bats.
ACKNOWLEDGEMENTS
I thank the organizers of the symposium for including
me on the program as well as those who read and
commented on earlier versions of this manuscript,
including Rafa Avila-Flores, Enrico Bernard, Stefania Biscardi,
Herman Limpens, Brian Keeley, Liz Reddy and
Hannah ter Hofstede. My research on bats has been supported
by research grants from the Natural Sciences and
Engineering Research Council of Canada.
LITERATURE CITED
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Bat Echolocation Research: tools, techniques & analysis