Dean A. Waters

The distribution of Daubenton's bats (Myotis daubentonii) and pipistrelle bats (Pipistrellus pipistrellus) (Vespertilionidae) in relation to small-scale variation in riverine habitat.

The distribution of foraging Myotis daubentonii and Pipistrellus pipistrellus bats (Vespertilionidae) was investigated along an upland river in relation to the smoothness of the water surface and the extent of bankside vegetation. It was found that both bat species significantly preferred sections of the river with smooth water surfaces and trees on both banks. The abundance of insects flying just above the water surface was also significantly greater in sections with a smooth water surface with trees on both sides. The distribution of bats thus probably correlated with the higher densities of insects, and may also have been related to the avoidance of noise from rough water areas which interferes with echolocation. The results suggest that in upland river systems, maintenance and enhancement of bankside vegetation and tree cover in association with the maintenance and enhancement of a mosaic of water surfaces (to include some smooth water where trees are present) will increase the value of the riverine habitat to bats.

Echolocation call design and limits on prey size: a case study using the aerial-hawking bat Nyctalus leisleri

The echolocation calls used by Nyctalus leisleri during search phase in open air space are between 9 and 14 ms long, with the peak energy between 24 and 28 kHz. The pulses are shallowly frequency-modulated with or without an initial steep frequency-modulated component. The diet consists primarily of small flies (Diptera), including many chironomids (wingspan 9–12 mm) and yellow dung flies (Scatophaga; wingspan 24 mm), but also of some larger insects such as dung beetles (Coleoptera; Scarabaeoidea), caddis-flies (Trichoptera) and moths (Lepidoptera). The echo target strength of some prey items was measured. Contrary to models based on standard targets such as spheres or disks, the echo strength of real insects was found to be virtually independent of the emitted frequency within the 20–100 kHz frequency range. A model was used to calculate probable detection distances of the prey by the bat. Using narrow-band calls of 13.7 ± 2.7 ms duration, a bat would detect the two smallest size classes of insect at greatest range using calls of 20 kHz. The results may therefore explain why many species of large and medium sized aerial-hawking bats use low-frequency calls and still eat mostly relatively small insects. The data and model challenges the assumption that small prey are unavailable to bats using low-frequency calls.

Bats and moths: what is there left to learn?

Abstract.  Over 14 families of moths have ears that are adapted to detect the ultrasonic echolocation calls of bats. On hearing a bat, these moths respond with an escape response that reduces their chances of being caught. As an evolutionary response, bats may then have evolved behavioural strategies or changes in call design to overcome the moths hearing. The nature of this interaction is reviewed. In particular, the role of the echolocation calls of bats in the shaping of the structure, neurophysiology and behavioural responses of moths is discussed. Unresolved issues, such as the structural complexity of the moths auditory system, the nature of temporal integration and the role of the non‐auditory B cell, are described. Issues in which the interactions between bats and moths may be of more general interest to biologists, such as noise filtering within the central nervous system, protean behaviours and coevolution between predator and prey, are also discussed. The interaction between bats and moths has much to interest general biologists, and may provide a useful model in understanding the neurophysiological basis of behaviour, including protean escape behaviours. The validity of the term coevolution as applied to this system is discussed, as there is no doubt that the auditory system of moths is a response to the echolocation calls of bats, although the evolutionary response of bats to moths is more ambiguous.

Echolocation signal structure in the Megachiropteran bat Rousettus aegyptiacus Geoffroy 1810.

SUMMARY Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described. Although thought to have a simple echolocation system compared to that of Microchiroptera, R. aegyptiacus is capable of good obstacle avoidance using its impulse sonar. The energy content of the signal was at least an order of magnitude smaller than in Microchiropteran bats and dolphins (approximately 4×10–8 J m–2). Measurement of the duration, amplitude and peak frequency demonstrate that the signals of this animal are broadly similar in structure and duration to those of dolphins. Gabor functions were used to model signals and to estimate signal parameters, and the quality of the Gabor function fit to the early part of the signal demonstrates that the echolocation signals of R. aegyptiacus match the minimum spectral spread for their duration and amplitude and are thus well matched to its best hearing sensitivity. However, the low energy content of the signals and short duration should make returning echoes difficult to detect. The performance of R. aegyptiacus in obstacle avoidance experiments using echolocation therefore remains something of a conundrum.

The influence of bat detector brand on the quantitative estimation of bat activity

ABSTRACT Bat detectors are commonly used to monitor bat behaviour. Earlier research has suggested that there may be systematic differences in the response of different detectors to bat calls. Such differences would have important implications for the comparability of quantitative surveys conducted with bat detectors. The present study examines variability within and between brands of bat detector in accuracy of tuning, directionality and sensitivity to different types of bat echolocation call in bat detectors from three manufacturers. The consistency of results from a field survey incorporating the three brands in a standardised methodology are also examined. Significant differences were found within and between brands in directionality and sensitivity which would lead to bias in bat surveys. The implications of these findings for bat surveys are discussed, as are the design features of importance for species identification.

Echolocation Performance and Call Structure in the Megachiropteran Fruit-Bat Rousettus aegyptiacus

The structure of the calls made by the echolocating fruit bat Rousettus aegyptiacus while flying within a flight tunnel were investigated. Calls are impulsive clicks lasting around 250 &mgr;s, with most energy occurring during the first 100 &mgr;s. Such a call duration is much shorter than that previously reported for this species. The ability of R. aegyptiacus to detect and avoid obstacles was tested in both the light and total darkness. Bats were able to detect and avoid 6 mm diameter wires significantly more often than 1.3 mm diameter wires when tested in the light. In the dark, the same relationship held, with no decrease in the ability to detect and avoid the obstacles. Bats used echolocation in both the light and the dark conditions. The simple impulsive clicks used in echolocation by this species are thus able to detect wires of at least 6 mm in diameter and probably smaller. The detection problems associated with very short duration signals is discussed. The possession of both a good visual system, and a good echolocation system in this species has implications for the evolution of echolocation in bats.

Time-frequency and advanced frequency estimation techniques for the investigation of bat echolocation calls

In this paper, techniques for time-frequency analysis and investigation of bat echolocation calls are studied. Particularly, enhanced resolution techniques are developed and/or used in this specific context for the first time. When compared to traditional time-frequency representation methods, the proposed techniques are more capable of showing previously unseen features in the structure of bat echolocation calls. It should be emphasized that although the study is focused on bat echolocation recordings, the results are more general and applicable to many other types of signal.

Using bat-modelled sonar as a navigational tool in virtual environments

Bats are able to use active sonar as a mechanism for locating object in three dimensions and for generating spatial maps of their environments. Humans use passive sound cues to detect features of the space they occupy, as well as react to the spatial location of objects which generate sound. The system described in this paper allows free-ranging humans to locate a virtual sound location using active sonar. An emitted pulse, centred on the users head, serves as an intensity and time marker. The return pulse is rendered at the virtual target location and emitted after a time delay corresponding to the two-way path from sender to target and back again. The sonar system is modelled on those of bats, using ultrasonic frequency-modulated signals reflected from simple targets. The model uses the reflectivity characteristics of ultrasound, but the frequency and temporal structure used are scaled, with the speed of sound being set to 8.5ms^-^1 to bring the frequency range and temporal resolution within the capabilities of the human auditory system. Orientation with respect to the ensonified target is achieved by time-of-flight time delays to give target range, and binaural location information derived from interaural timing differences, interaural intensity differences, and head-related transfer functions. Subjects performed significantly better at a localization task when given temporal data based on echo delays with an outgoing reference pulse than without a reference pulse. Frequency-modulated signals sweeping from 1.5kHz-100Hz over 500ms provide the best localization cues, and users found them significantly easier to locate than continuous sounds.

Mobility AT: The Batcane (UltraCane)

The use of the long cane by visually impaired people as an obstacle detector is long standing. More recently the basic cane design has been equipped with laser or ultrasound transmitters and sensors and an interpretive human interface to improve its effectiveness, the objective being to allow safe travel by a visually impaired person. This chapter reports an important case study of the steps involved indeveloping an advanced technology obstacle avoidance cane that used bat echolocation signal processing techniques and ultrasonic technology. The final cane design is now marketed worldwide as the UltraCane™.

Echolocation signals and pinnae movement in the fruitbat Rousettus aegyptiacus

ABSTRACT The fruit bat Rousettus aegyptiacus has highly mobile pinnae. Little is known about the role that such movements play in sound localisation however and whether they interact with the process of echolocation in this species. Here we report the correspondence of echolocation signals in free flight with the downward wingbeat and forward movement of the pinnae, and demonstrate that the ears have a greater sensitivity to click stimuli in front of the animal when directed forwards than when back and to the side. The potential significance of the production of echolocation signals whilst the ears are moving from their least sensitive to their most sensitive position is discussed.