Bat Echolocation Researc h - Bat Conservation International

Figure 5: Variation in the echolocation calls of Eptesicus serotinus. From
left to right, calls are from individuals foraging at progressively lower
heights above the ground (height indicated under each call). Redrawn
from Jensen and Miller 1999.
does aerial hawking. It is thus not surprising that species
that use both foraging styles vary their calls depending
on their foraging behavior (Faure and Barclay 1994).
Myotis evotis, for example, uses quieter calls and does not
produce a feeding buzz when gleaning. If conspecifics in
different locations forage in different ways, perhaps
because prey resources differ, for example, then the
echolocation calls they use may also differ.
Prey characteristics may affect the type of echolocation
calls used by bats (Leippert et al. 2002). Some prey,
such as some moths, can detect the echolocation calls of
bats, and this defense may have favored the evolution of
specific echolocation features such as high or low frequency,
low intensity, or short duration (Fenton and
Fullard 1979). Characteristics of different prey communities
within the geographic range of a bat species may
thus have resulted in geographic variation in echolocation
calls. Because the frequency of a sound and its corresponding
wavelength also influence the strength of
the returning echo from targets of different size (Hartley
1989), the size of prey available in an area could also
potentially favor certain echolocation call designs.
Specifically, the need to detect smaller prey should favor
the use of higher-frequency calls. If so, and prey size
varies over a bat species’ range, echolocation calls might
also vary geographically.
Finally, the presence of conspecifics and other
species may influence the type of echolocation calls
individuals use. Individuals of several species modify
their calls in the presence of conspecifics (Obrist 1995).
At a minimum, this will increase the amount of variation
in call characteristics in a particular location and thus
make species identification more difficult.
use constant frequency (CF) echolocation calls, considerable
geographical variation occurs in the CF frequency
(e.g., Francis and Habersetzer 1998; Guillén et al. 2000;
Heller and von Helversen 1989; Figs. 6 and 7). Variation
in body size does not provide a satisfactory explanation
in many of these cases. However, among the subspecies
of hoary bat (Lasiurus cinereus), body size does correlate
with significant geographic variation in echolocation call
characteristics (Barclay et al. 1999; Fig. 4). There is also
geographic variation in call structure in both species of
New Zealand bats, and this variation may be related to
body size or subspecies differences, although data are
limited (Parsons 1997). In other cases, geographic variation
in call structure has been documented in various
species, but no functional explanation has been determined
(Murray et al. 2001; Thomas et al. 1987).
CONSEQUENCES OF GEOGRAPHIC VARIATION
AND RECOMMENDATIONS
Despite limited study, there is evidence that the
echolocation calls of a number of species vary geographically
and there are both physical and adaptive reasons
to expect such variation. Although in some cases,
geographic variation may not be great enough to cause
Figure 6: Geographic variation in the echolocation calls of Hipposideros
cervinus. The upper call is typical of individuals from peninsula
Malaysia, and the lower of individuals from Sabah, Borneo (data from
Francis and Habersetzer 1998).
GEOGRAPHIC VARIATION AT A LARGER SCALE
Although few studies have specifically assessed geographic
variation in bat echolocation, there is evidence
that the echolocation call characteristics of some species
of bats do vary geographically across the species’ ranges.
Among various rhinolophid and hipposiderid bats that
Section 4: Resources, Research and Study
Figure 7: Variation in the echolocation calls of Hipposideros ruber. The
upper two calls represent average values for individuals from a colony in
Rio Muni, and the lower two calls are for individuals from a colony on
the island of São Tomé. In each pair, the upper call is typical of males
and the lower is typical of females.
147