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Scaling of Wingbeat and Echolocation Pulse Emission Rates in Bats: Why are Aerial Insectivorous Bats so Small?
Vol. 8, No. 4 (Aug., 1994), pp. 450-457
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2390068
Page Count: 8
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1. It has been proposed that echolocating bats normally emit one call per wingbeat when searching for prey. The coupling of sound production with flapping makes the production of intense sound pulses cost no more in energetic terms than beating the wings and not calling, whereas calling without flapping would be energetically expensive. The scaling of wingbeat frequency and pulse repetition rate with body mass was investigated in a cross-species analysis to test the hypothesis that calling and flapping are coupled in echolocating bats. 2. For 57 species where measurements of pulse repetition rate were available, most bats (75%) emitted 0.5-2 pulses per predicted wingbeat during search phase. In some fast-flying bats (12% of sample), fewer than the predicted one pulse per beat were produced, perhaps because such bats skipped calling during some wingbeats, or possibly because wingbeat frequencies were very slow when the bats were cruising in open habitats. A few species (12%) appeared to produce several pulses per wingbeat. Such species were gleaners, and often produced low-intensity calls. For bats which emitted intense calls and foraged largely by aerial hawking, pulse repetition rate scaled as body mass (M)-0.775. In echolocating bats, wingbeat frequency scaled as M-0.326. 3. Aerial feeding bats typically emit intense search phase calls, and it is concluded that such bats normally produce one or fewer pulses per wingbeat during search phase, as predicted by the coupling hypothesis. Coupling may constrain maximal body size in aerial insectivorous bats because very large bats may be unable to echolocate at a sufficiently high rate to catch enough insects to meet the high energetic demands associated with large size. Some bats may be able to trade-off call intensity against repetition rate, however, and produce several low-intensity pulses per wingbeat. These bats were usually gleaners. Bats in the family Hipposideridae appear to have specialized echolocation which allows the production of several high-intensity calls per wingbeat.
Functional Ecology © 1994 British Ecological Society