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PLoS One
2010 Sep 17;59:. doi: 10.1371/journal.pone.0012842.
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Variability in echolocation call intensity in a community of horseshoe bats: a role for resource partitioning or communication?
Schuchmann M
,
Siemers BM
.
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BACKGROUND: Only recently data on bat echolocation call intensities is starting to accumulate. Yet, intensity is an ecologically crucial parameter, as it determines the extent of the bats'' perceptual space and, specifically, prey detection distance. Interspecifically, we thus asked whether sympatric, congeneric bat species differ in call intensities and whether differences play a role for niche differentiation. Specifically, we investigated whether R. mehelyi that calls at a frequency clearly above what is predicted by allometry, compensates for frequency-dependent loss in detection distance by using elevated call intensity. Maximum echolocation call intensities might depend on body size or condition and thus be used as an honest signal of quality for intraspecific communication. We for the first time investigated whether a size-intensity relation is present in echolocating bats.
METHODOLOGY/PRINCIPAL FINDINGS: We measured maximum call intensities and frequencies for all five European horseshoe bat species. Maximum intensity differed among species largely due to R. euryale. Furthermore, we found no compensation for frequency-dependent loss in detection distance in R. mehelyi. Intraspecifically, there is a negative correlation between forearm lengths and intensity in R. euryale and a trend for a negative correlation between body condition index and intensity in R. ferrumequinum. In R. hipposideros, females had 8 dB higher intensities than males. There were no correlations with body size or sex differences and intensity for the other species.
CONCLUSIONS/SIGNIFICANCE: Based on call intensity and frequency measurements, we estimated echolocation ranges for our study community. These suggest that intensity differences result in different prey detection distances and thus likely play some role for resource access. It is interesting and at first glance counter-intuitive that, where a correlation was found, smaller bats called louder than large individuals. Such negative relationship between size or condition and vocal amplitude may indicate an as yet unknown physiological or sexual selection pressure.
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20862252
???displayArticle.pmcLink???PMC2941460 ???displayArticle.link???PLoS One
Figure 1. CF frequencies of sympatric horseshoe bats from Bulgaria are plotted against forearm length, the standard size measure in bats, for Rhinolophus ferrumequinum (Rf, N = 25), R. blasii (Rb, N = 56), R. mehelyi (Rm, N = 85), R. euryale (Re, N = 116) and R. hipposideros (Rh, N = 10).The peak echolocation call frequencies used by Rm strongly overlapped those of Re and Rh (dotted lines), while the bands used by Rf and Rb were clearly separated.
Figure 3. Intraspecific call intensity relations and intra-individual variation.Averaged call intensities of the six highest intensities of each individual (in dB SPL; calculated for 10cm distance to the bats' nose) for individual R. ferrumequinum (Rf, N = 12), R. blasii (Rb, N = 6), R. mehelyi (Rm, N = 11), R. euryale (Re, N = 12) and R. hipposideros (Rh, N = 10) are plotted against the corresponding averaged peak echolocation call frequencies. Error bars show the corresponding standard deviations.
Figure 4. Intraspecific call intensity relations.Call intensities (in dB SPL; calculated for 10cm distance to the bats' nose) for individual R. ferrumequinum (Rf, N = 12), R. mehelyi (Rm, N = 11), R. euryale (Re, N = 12) and R. hipposideros (Rh, N = 10) are plotted against A: forearm length (FA), B: body mass index (BMI) and C: body mass. For statistics, see text. (Rb only used for Fig. 3 because of missing body size data)
Figure 5. Estimated maximum prey detection distances for the five European species of horseshoe bat.The dark grey bars indicate maximum detection distances for large insects (target strength (TS) = −30 dB) for either an echo perception threshold (thresh) of 0 dB SPL or 20 dB SPL; the light grey bars show maximum detection distances for small insects (target strength (TS) = −60 dB) for either an echo perception threshold of 0 dB SPL or 20 dB SPL. Calculations were based on average maximum call intensities and an average peak echolocation call frequency as measured in this study. Species abbreviations as in the other figures. ‘Rm scaled’ indicated detection distances R. mehelyi would experience if the species called at the intensity we measured, but at a frequency as predicted by allometric scaling (97 kHz instead of 108 kHz).
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