Bat Echolocation Researc h - Bat Conservation International

y the African bat Cardioderma cor (Megadermatidae). Journal
of Comparative Physiology A161:59-66.
SCHNITZLER, H.-U., and E. K. V. KALKO. 2001. Echolocation
by insect-eating bats. Bioscience 51:557-569.
SCHUMM, A., D. KRULL, and G. NEUWEILER. 1991.
Echolocation in the notch-eared bat, Myotis emarginatus.
Behavioral Ecology and Sociobiology 28:255-261.
SIEMERS, B. M., P. STILZ, and H.-U. SCHNITZLER. 2001.
The acoustic advantage of hunting at low heights above
water: behavioral experiments on the European ‘trawling’
bats Myotis capaccini, M. dasycneme and M. daubentoni. The
Journal of Experimental Biology 204:3843-3854.
SIMMONS, J. A., and R. A. STEIN. 1980. Acoustic imaging
in bat sonar: echolocation signals and the evolution of
echolocation. Journal of Comparative Physiology
A135:61-84.
SUTHERS, R. A. 1970. Vision, olfaction and taste. Pp. 265-
309 in Biology of bats. Volume II (W. A. Wimsatt, ed.).
Academic Press, New York.
THIES, W., E. K. V. KALKO, and H.-U. SCHNITZLER.
1998. The roles of echolocation and olfaction in two
neotropical fruit-eating bats, Carollia perspicillata and C. castanea,
feeding on Piper. Behavioral Ecology and Sociobiology
42:397-409.
VERBOOM, B., A. M. BOONMAN, M. BOONMAN, and H.
J. G. A. LIMPENS. 1999. Acoustic perception of landscape
elements by the pond bat (Myotis dasycneme). Journal of
Zoology (London) 248:59-66.
VON HELVERSEN, D., and O. VON HELVERSEN. 1999.
Acoustic guide in bat-pollinated flower. Nature 398:759-
760.
VON HELVERSEN, D., M. W. HOLDERIED, and O. VON
HELVERESEN. 2003. Echoes of bat-pollinated, bellshaped
flowers: conspicuous for nectar-feeding bats? Journal
of Experimental Biology 206:1025-1034.
WILLIAMS, T. C., J. M. WILLIAMS, and D. R. GRIFFIN.
1966. The homing ability of the neotropical bat Phyllostomus
hastatus. Science 155:1435-1436.
THE PAST AND FUTURE HISTORY OF BAT DETECTORS
DONALD R. GRIFFIN
Deceased
Work done at
Concord Field Station, Harvard University, Old Causeway Road, Bedford MA 01730, United States
What we can learn about the echolocation abilities of bats has been limited by the sensitivity of microphones; and
some of their high-frequency sounds cannot be detected under many conditions, even with the best instruments currently
available. For example, sensitive heterodyne bat detectors sometimes fail to detect feeding buzzes from Myotis
lucifugus on early summer evenings when they are obviously catching insects. By mounting the bat detector on a long
pole and using infrared video showing the bat and the insect it captured, we found that buzzes were detectable only
if the microphone was within one or two meters of the bat. Yet at other times buzzes could be detected from the
same bats in the same location at distances of ten meters. Many neotropical bats emit much fainter sounds than M.
lucifugus, and there is some evidence that shrews and laboratory rats use echolocation, although it has been difficult
to detect whatever sounds they may be emitting. There is an “apparatus threshold” which is ordinarily well above
the auditory thresholds of bats and shrews, so that there is a sizeable intensity range where we cannot yet determine
whether sounds are being used for echolocation or communication.
Key words: bat detectors, echolocation, equiptment, insect capture by bats, microphone sensitivity, Myotis lucifugus
6
PAST HISTORY
To study the echolocation abilities of bats it is first
necessary to detect their orientation sounds. The fact
that bats make ultrasonic sounds was discovered by
means of G. W. Pierce’s “sonic amplifier,” which was a
heterodyne detector with an audio output constructed
by modifying an AM radio receiver (Pierce and Griffin
1938). This apparatus had been developed to study the
sounds of insects; its circuit is described by Noyes and
Pierce (1937) and the microphones by Pierce (1948).
The essential first element in any apparatus for detecting
bat sounds is the microphone. Pierce used magnetostriction
transducers and Rochelle salt crystals as microphones;
the latter were somewhat more sensitive, but
neither was calibrated nor nearly as sensitive as microphones
developed later. Pierce’s apparatus displayed the
heterodyne output graphically, but its temporal resolution
was not adequate to measure the duration of the
ultrasonic orientation sounds used by bats of the family
Vespertilionidae. It could record pulse repetition rates
and revealed that the interpulse interval dropped by
about half when Myotis lucifugus avoided small wires
(Galambos and Griffin 1942). Furthermore it enabled us
to demonstrate that emission and reception of orientation
sounds were necessary for obstacle avoidance (Griffin
and Galambos 1941; Griffin 1958).
The next step was to use the Western Electric 640
Bat Echolocation Research: tools, techniques & analysis