Intra- and Interspecific Variability of Echolocation Pulse Acoustics in the African Megadermatid Bats

Abstract

The yellow-winged bat, Lavia frons, and the heart-nosed bat, Cardioderma cor, are sympatric species of the family Megadermatidae resident to East Africa. Cardioderma cor roost in groups and disperse to individual foraging areas at night, whereas L. frons roost in male-female pairs in Acacia trees within a foraging territory. Nightly foraging areas overlap across species, and thus interspecific differences in echolocation may reflect niche differences crucial for coexistence. Here we compare differences in echolocation from hand-released C. cor and L. frons, and L. frons individuals recorded during fly-bys. Furthermore, megadermatids display a host of social behaviors, including territoriality and singing, and thus intraspecific differences in echolocation may be important for facilitating behavior in this family but has not yet been assessed. We report the patterns of variability of echolocation by sex, body size, and individual of C. cor. We measured 354 pulses from 17 C. cor individuals and 35 pulses from four L. frons individuals in Tanzania. Up to four harmonics were observed in both C. cor and L. frons, with the second and third harmonics emphasized and the first suppressed. Cardioderma cor is a surface gleaner while L. frons is an aerial-hawker, and clear differences in frequency metrics (Fmin, Fmax, Fpeak) and duration reflect this. We measured 17 variables including temporal, frequency, and shape metrics for intraspecific C. cor pulse analyses. A MANOVA testing individuality on five principle components was significant, but performed poorly in a discriminant analysis. Body mass and forearm length did not correlate with any pulse metrics. Males had significantly lower Fmin and frequency contour parameters than females, although males were slightly smaller than females. These results suggest that L. frons and C. cor have clear interspecific differences in pulse acoustics that align with guild differences, and may serve heterospecific discrimination, while some intraspecific difference in C. cor, particularly by sex, are suggestive of other factors beyond navigation that influence pulse variability.