Nature 350, 421 - 423 (04 April 1991); doi:10.1038/350421a0

No cost of echolocation for bats in flight

J. R. Speakman & P. A. Racey

Department of Zoology, University of Aberdeen, Aberdeen AB9 2TN, UK

ECHOLOCATION has evolved in relatively few animal species¹. One constraint may be the high cost of producing pulses, the echoes of which can be detected over useful distances². The energy cost of echolocation in a small (6 g) insectivorous bat, when hanging at rest, was recently measured at 0.067 Joules per pulse³, implying a mean cost for echolocation in flight of 9.5 basal metabolic rate (range 7 to 12). Because flight is very costly⁴, whether the costs of echolocation and flying are additive is an important question. We measured the energy costs of flight in two species of small echolocating Microchiroptera using a novel combination of respirometry and doubly-labelled water⁵. Flight energy expenditure (adjusted for body mass) was not significantly different between echolocating bats and non-echolocating bats and birds. The low cost of echolocation for flying vertebrates may have been a significant factor favouring its evolution in these groups.

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