Lancaster, W.C.*; Ward, S.; Jones, G.; Speakman, J.R.: Energetics of Biosonar Vocalization in Stationary Insectivorous Bats
Previous studies show a linkage between flight and production of biosonar calls in bats. Microchiropteran bats also emit a wide variety of calls while at rest including biosonar calls of high intensity in some species. The propensity of bats to make echolocation calls at rest is variable and studies suggest that energetic constraints may underlie this variability in behavior. We measured the energetic expenditure associated with biosonar call production at rest in five species of insectivorous bats using respirometry. The species use distinct modes of foraging and this is reflected in call structure, intensity and phrasing. Oxygen consumption associated with vocalization increased with rate of call production. The slope of the plot of watts vs. call rate gives mean cost per call. This cost was greatest in Eptesicus serotinus at 0.22 J/call, was 0.19 in Myotis myotis, 0.12 in Pipistrellus pipistrellus, 0.03 in Pteronotus parnellii and in Rhinolophus ferrumequinum was 0.03 J/call. Costs per call were inversely related to the species’ propensity to produce calls at rest. In three species where data are available, energy flux density of calls averaged 7.63 x 10-7J/m2 in R. ferrumequinum, 3.69 x 10-7 in P. pipistrellus and 2.30 x 10-7 in M. myotis. In the other species, P. parnellii has calls of similar intensity and duty cycle to R. ferrumequinum and E. serotinus is similar to Pipistrellus. Bats that produce the most vocal energy at rest are expending the least amount of energy in doing so. We suggest that these species have behavioral and morphological adaptations to reduce the cost and increase the efficiency of producing biosonar calls at rest. Funded by BBSRC(UK) 1/S04245.
