The function of modified echolocation pulses in horseshoe bats (Family: Rhinolophidae)

Netshongolwe, Tshifhiwa

The function of modified echolocation pulses in horseshoe bats (Family: Rhinolophidae)

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Biological Sciences

Faculty

Faculty of Science

Abstract

Recent studies suggest that echolocation pulses may be implicated in communication. In one of these studies, the horseshoe bat, Rhinolophus clivosus, was found to emit echolocation pulses with an unusual and pronounced upsweep at the end of the echolocation pulse (at the FM component). It was hypothesized that these “modified echolocation pulses” may serve a communication function, enabling horseshoe bats to echolocate and communicate at the same time. This study investigated the function of these modified echolocation pulses. Hand-held recordings from several species of horseshoe bats were surveyed to determine how widespread modified pulses are within the family of Rhinolophidae. Modified echolocation pulses were found to be emitted by 11 out of 12 horseshoe bat species considered in this study. These species are distributed across several genetic subgroups of rhinolophid species. Four of them are in the capensis clade, R. capensis, R. simulator, R. swinnyi and R. denti, five of them R. damarensis, R. eloquens R. hildebrandtii, R. fumigatus and R. darlingi, in the fumigatus clade, one in the landeri clade (R. landeri), and two in the ferrumequinum clade (R. clivosus and R. ferrumequinum). These results suggest that only R. maendeleo from the Adami clade did not emit modified echolocation pulses. However, the absence of modified echolocation pulses in R. maendeleo is more likely than not due to the small sample size for this species (three individuals, Fig. 6). Gathered from these results is that modified pulses are not randomly emitted because they are not emitted in specific clades but across the clades and species. I tested the prediction that modified echolocation pulses are emitted in the presence of other bats by comparing emission rates across conditions that present different social valences, for example, solitary bats during foraging and bats flying in a flight cage in the presence of conspecifics. I surveyed different conditions namely: foraging, emerging from a roost, bats kept in a captive group and hand-held. I did experiments in which bats were exposed to different social valences in a controlled environment. There was a significant difference in the number of modified pulses across species, N=1309, H= 907.02, 4 d.f, p<0.05 (Fig.9). In flight- room experiments, the social contexts in which these modified pulses were emitted were further investigated, using R. capensis, as a model species. In the first experiment, R. capensis individuals were flown under different conditions, either alone, while sequences of standard and modified pulses of conspecifics were played back, or with conspecifics or with heterospecifics present in the flight- room. R. capensis emitted modified echolocation modified pulses in all conditions including when they flew alone. However, there were significant differences in the number of modified pulses emitted amongst the different conditions (N=19, χ2=6.00, 2 d.f, p=0.04). In standard echolocation pulses (i.e. without the modification), the FM component plays a role in distance measuring (ranging) and the modification of the FM component may affect this very important function. A second experiment was therefore conducted during which bats were flown on an obstacle course to determine if modified pulses adversely affected the ranging ability of bats. If so, bats should not emit modified echolocation pulses in conditions, like an obstacle course, that require precise ranging information. R. capensis individuals (N=19) were held through four conditions each, namely: flying alone, flying with a conspecific, flying with a conspecific put in a small cage, and flying while conspecific pulses were being played back. There were no modified echolocation pulses emitted throughout all the conditions. Thus modified echolocation pulses were not emitted when precise ranging was required which suggests that the modification may have impaired the ranging function of the FM component. In conclusion, modified echolocation pulses were emitted more often when the bat was in the presence of other bats, which suggests that it may function as a communication signal. However, it appears that modified echolocation pulses may adversely impact the ranging function of the FM component so that bats were unable to use the modification when precise ranging is required.

Keywords

biological sciences

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