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1

small bats - the echolocating predators (Alcock, 2007)

Bats (Chiroptera):
Megachiroptera (150 species): large eyes, simple ears, non-echolocating (except Rousettus - clicking (HF, short, frequent pulses, in roosting caves)
Microchiroptera (800 species): small-sized, small eyes, complex ears, echolocation
○ Spallanzani (1794) and Jurin (1795) found that hearing essential for bats to avoid obstacles in flight
○ Griffin and Pierce (1938) discovered emission of high-freq ultrasonic pulses in flying bats
○ Ultrasound attenuates quickly - useful for short-distance object detection and tracking
○ Higher pitch = shorter sound travels
○ Sense vibrations - air movement v. close to body

Moths have tympanum on each side of body - compare input from each side - is sound louder on one side or other or behind - hear where bat is - respond to change in sound depending on wing

see notes

2

Small bats - the echolocating predators (Alcock, 2007) research

Mann et al. (2011)

Kalko (1995)

Götze et al. (2016)

Denzinger and Schnitzlet (2013)

Neuweiler (2003)

3

Mann et al. (2011)

Individual recognition via olfactory, auditory, or visual cues is crucial for animals to form and maintain stable social groups, particularly in large colonies such as those of Egyptian fruit bats (Rousettus acuptiacus). We tested whether Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifics, using two captive groups of male bats. We recorded the behavioural and auditory responses of focal animals in a binary choice experiment in which they could approach either members of their own social group or unfamiliar individuals. In general, bats preferred to stay close to other bats, familiar or unfamiliar, over resting alone and spent more time in close proximity to members of their own group than to unfamiliar conspecifics. The majority of bats interacted more with the unfamiliar individuals, although this result did not reach significance. We conclude that Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifies. Since only one individual emitted social calls and bats never produced echolocation calls during the experiment, we infer that individual recognition was most likely mediated via olfactory and/or visual cues. The ability to identify familiar individuals may indicate that males of Egyptian fruit bats form stable groups within their large colonies.

4

Kalko (1995)

The foraging and echolocation behaviour of three European pipistrelles (Pipistrellus pipistrellus, P. nithusii and P. kuhlii) was studied under natural conitions. The pipistrelles were photographed with two 35 mm cameras under stroboscopic illumination, and their echolocation signals were recorded simultaneously. This permits a three-dimensional reconstruction of the flight paths of bat and prey, and allows the details of echolocation behaviour to be studied in the context of natureal foraging behaviour. The general relationships between foraging and echolocation behaviour were consistent among the three species. Foraging behaviour consisted of four stages: search flight (before detection of prey), approach flight (pursuit after detection of prey), capture and retrieval of prey. These stages correlated with phases in echolocation behaviour: search, approach, and terminal phase followed by a pause. Detection of prey occurred at distances of 1·14−2·20 m. The search cone extending from the bat's mouth was up to 150° wide. The pipistrelles caught prey in mid-air, either with the tail membrane alone or by funnelling it with a wing onto the tail membrane. Except for some intra- and interspecific differences in sound duration, pulse interval, bandwidth and terminal frequency in search phase, the structure and pattern of the echolocation signals were similar in the three pipistrelles. In the approach and terminal phases, pulse duration and pulse interval decreased with the approach to the target, while bandwidth and sweeprate increased. While pursuing insects, the pipistrelles precisely avoided an overlap between outgoing signal and the echo returning from the prey. Furthermore, the bats stopped emitting signals several centimeters before they reached the insect.

5

Götze et al. (2016)

Frequency shifts in signals of bats flying near conspecifics have been interpreted as a spectral jamming avoidance response (JAR). However, several prerequisites supporting a JAR hypothesis have not been controlled for in previous studies. We recorded flight and echolocation behavior of foraging Pipistrellus pipistrellus while flying alone and with a conspecific and tested whether frequency changes were due to a spectral JAR with an increased frequency difference, or whether changes could be explained by other reactions. P. pipistrellus reacted to conspecifics with a reduction of sound duration and often also pulse interval, accompanied by an increase in terminal frequency. This reaction is typical of behavioral situations where targets of interest have captured the bat’s attention and initiated a more detailed exploration. All observed frequency changes were predicted by the attention reaction alone, and do not support the JAR hypothesis of increased frequency separation. Reaction distances of 1–11 m suggest that the attention response may be elicited either by detection of the conspecific by short range active echolocation or by long range passive acoustic detection of echolocation calls.

6

Denzinger and Schnitzler (2013)

Throughout evolution the foraging and echolocation behaviors as well as the motor systems of bats have been adapted to the tasks they have to perform while searching and acquiring food. When bats exploit the same class of environmental resources in a similar way, they perform comparable tasks and thus share similar adaptations independent of their phylogeny. Species with similar adaptations are assigned to guilds or functional groups. Habitat type and foraging mode mainly determine the foraging tasks and thus the adaptations of bats. Therefore, we use habitat type and foraging mode to define seven guilds. The habitat types open, edge and narrow space are defined according to the bats' echolocation behavior in relation to the distance between bat and background or food item and background. Bats foraging in the aerial, trawling, flutter detecting, or active gleaning mode use only echolocation to acquire their food. When foraging in the passive gleaning mode bats do not use echolocation but rely on sensory cues from the food item to find it. Bat communities often comprise large numbers of species with a high diversity in foraging areas, foraging modes, and diets. The assignment of species living under similar constraints into guilds identifies patterns of community structure and helps to understand the factors that underlie the organization of highly diverse bat communities. Bat species from different guilds do not compete for food as they differ in their foraging behavior and in the environmental resources they use. However, sympatric living species belonging to the same guild often exploit the same class of resources. To avoid competition they should differ in their niche dimensions. The fine grain structure of bat communities below the rather coarse classification into guilds is determined by mechanisms that result in niche partitioning

7

Neuweiler (2003)

This review is yet another attempt to explain how echolocation in bats or bat-like mammals came into existence. Attention is focused on neuronal specializations in the ascending auditory pathway of echolocating bats. Three different mechanisms are considered that may create a specific auditory sensitivity to echos: (1) time-windows of enhanced echo-processing opened by a corollary discharge of neuronal vocalization commands; (2) differentiation and expansion of ensembles of combination-sensitive neurons in the midbrain; and (3) corticofugal top-down modulations. The second part of the review interprets three different types of echolocation as adaptations to ecological niches, and presents the sophisticated cochlear specializations in constantfrequency/frequency-modulated bats as a case study of finely tuned differentiation. It is briefly discussed how a resonant mechanism in the inner ear of constantfrequency/frequency-modulated bats may have evolved in common mammalian cochlea

8

The echo

• Echo variation: direction, delay, amplitude, freq
• Factors: physical (wave propagation, diffraction), object range, object size, object distance, object velocity
• Bat produces sound - then listens to echo - sound hits surface in sufficient distance and echo returns - knows there's an object there - change in shape and freq - properties analysed to define whether large or small object

Calculate diffs between cry and echo returned - direction, speed, size of object - diff variables

see notes

Neuweiler (2003)
- See notes

9

The echo research

Thiagavel et al. (2018)

10

Thiagavel et al. (2018)

Substantial evidence now supports the hypothesis that the common ancestor of bats was nocturnal and capable of both powered flight and laryngeal echolocation. This scenario entails a parallel sensory and biomechanical transition from a nonvolant, vision-reliant mammal to one capable of sonar and flight. Here we consider anatomical constraints and opportunities that led to a sonar rather than vision-based solution. We show that bats’ common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that among extant predatory bats (all of which use laryngeal echolocation), those with putatively less sophisticated biosonar have relatively larger eyes than do more sophisticated echolocators. We contend that signs of ancient trade-offs between vision and echolocation persist today, and that non-echolocating, phytophagous pteropodid bats may retain some of the necessary foundations for biosonar.

11

deflection of basilar membrane

Voldrich (2009)

Frank and Kossl (1995)

12

Voldrich (2009)

A fresh basilar membrane has different mechanical properties in the radial and in the longitudinal directions. When pressure with a needle is exerted on the basilar membrane, a narrow radially oriented strip is deflected. The form of the deflection can be deduced from the pathological consequences of the acoustic trauma as well. The observed anisotrophy is a property of the vital membrane and is disturbed by chemical and physical influences and is lost post mortem. The post-mortem changes can explain the results obtained by von Bekesy which differ from ours. The physiological meaning of the mechanical properties of the basilar membrane is discussed here.

13

Frank and Kossl (1995)

so-suppression tuning curves (STCs) of the 2f(1)-f(2) distortion product (dp) were measured over a primary frequency range of 20 to 93 kHz in mustached bats, Pteronotus pamellii pamellii. Primary levels were chosen to produce dp levels between 0 and 7 dB SPL. At frequencies outside the ranges of 60 - 72 kHz and 90 - 93 kHz the shapes of the STCs were symmetrical or asymmetrical with a steep high frequency slope. In the vicinity of 61 kHz where a strong stimulus frequency otoacoustic emission (SFOAE) is present, the asymmetry of the STCs was inverted with a very steep low frequency slope(max. -89 dB/kHz) and a shallow high frequency slope. The inverted STCs resemble neuronal tuning curves of the same species with best frequencies at about 61 kHz. Close to 61 kHz the STCs were sharply tuned with Q(10dB) values up to 177. The STC-thresholds were about 20 dB above the neuronal thresholds. Thickenings of the basilar membrane located just basal to the cochlear place of the SFOAE frequency are probably involved in creating the asymmetric STCs. Cochlear resonance at the SFOAE frequency and an increased longitudinal coupling within the thickened basilar membrane region are thought to contribute to the specialized STC shape. In the range of 40 - 93 kHz, the STCs are also sharply tuned with inverted asymmetry which is probably not due to an harmonic effect of the specialized cochlear mechanics in the 60 kHz region but may be caused by an independent mechanism.

14

Harmonics in the vocalisations of bats

• Natural sounds are not pure tones - besides noise, there can be harmonics and overtones

Sounds produced by instruments, singing birds and vocalising bats contain harmonics - harmonic freqs multiples of fundamental freq

see notes

• Greater horseshoe bat Rhinopholus ferrmequinum: broadcast freq is 2nd harmonic (loudest freq band, preferred freq is around 83 kHz)
• Reduce octaves by changing length of string

Broadcast in frequency

Neuweiler (2003)
• FM signals (broadband) - excellent for distance and texture analysis

CF signals (constant freq, narrow band) - excellent for analysis of object movement and object detection over very large range (long pulses, higher energy) - distorts sound when object moves through it - Doppler effect
- See notes

15

Harmonics in the vocalisations of bats research

Motamedi and Muller (2014)

Bates et al. (2011)

16

Motamedi and Muller (2014)

The biosonar beampatterns found across different bat species are highly diverse in terms of global and local shape properties such as overall beamwidth or the presence, location, and shape of multiple lobes. It may be hypothesized that some of this variability reflects evolutionary adaptation. To investigate this hypothesis, the present work has searched for patterns in the variability across a set of 283 numerical predictions of emission and reception beampatterns from 88 bat species belonging to four major families (Rhinolophidae, Hipposideridae, Phyllostomidae, Vespertilionidae). This was done using a lossy compression of the beampatterns that utilized real spherical harmonics as basis functions. The resulting vector representations showed differences between the families as well as between emission and reception. These differences existed in the means of the power spectra as well as in their distribution. The distributions were characterized in a low dimensional space found through principal component analysis. The distinctiveness of the beampatterns across the groups was corroborated by pairwise classification experiments that yielded correct classification rates between similar to 85% and similar to 98%. Beamwidth was a major factor but not the sole distinguishing feature in these classification experiments. These differences could be seen as an indication of adaptive trends at the beampattern level. 

17

Bates et al. (2011)

When echolocating big brown bats fly in complex surroundings, echoes arriving from irrelevant objects (clutter) located to the sides of their sonar beam can mask perception of relevant objects located to the front (targets), causing "blind spots." Because the second harmonic is beamed more weakly to the sides than the first harmonic, these clutter echoes have a weaker second harmonic. In psychophysical experiments, we found that electronically misaligning first and second harmonics in echoes (to mimic the misalignment of corresponding neural responses to harmonics in clutter echoes) disrupts the bat's echo-delay perception but also prevents clutter masking. Electronically offsetting harmonics to realign their neural responses restores delay perception but also clutter interference. Thus, bats exploit harmonics to distinguish clutter echoes from target echoes, sacrificing delay acuity to suppress masking.

18

What does a bat need to know to locate prey? (Carew, 2000)

• Distance to object - orient towards and whether close enough to catch
• Size of object (loudness/amplitude of echo = subtended angle - size and distance correlated) - how much weaker is echo than amplitude of initial sound
• Location of object
• Moving (Doppler shift - shift in the pitch) or stationary object (no Doppler effect)
- Texture of object
- See notes

19

What does a bat need to know to locate prey? (Carew, 2000) research

Griffin et al. (1960)

Webster and Griffin (1962)

20

Griffin et al. (1960)

○ 1 . Bats of the genus Myotis (M. lucifugus, M. subulatus leibii and M. keenii septentrionalis) have been studied while pursuing and capturing small insects under laboratory conditions . It is apparently important to provide fairly large numbers of such insects in order to elicit insect catching behaviour indoors .
○ 2 . Insect catches are individually directed pursuit manoeuvres ; each insect is detected, located, and intercepted in flight within about half a second .
○ 3 . Certain individual bats caught mosquitos (Culex quinquefaciatus) and fruit flies (Drosophila robusta and D. melanogaster) at remarkably high rates which could be measured conservatively by the gain in weight of the bat . Sometimes a bat would average as many as 10 mosquitos or 14 fruit flies per minute during a period of several minutes. In four cases motion pictures showed two separate Drosophila catches within half a second .
○ 4. The orientation sounds of the hunting bat are adjusted in a manner that seems appropriate for the echolocation of single insects one at a time . There is a search phase before the occurrence of any apparent reaction to the insect . In this phase the frequency drops from about 100 to 50 kilocycles during each pulse of sound, and the pulses are emitted by M. lucifugus at intervals of 50 to 100 milliseconds .
○ 5 . When an insect is detected the search phase gives way to an approach phase characterized by a progressive shortening of the pulse-to-pulse interval and, if necessary, a sharp turn towards the insect . In this phase the pulse duration may shorten somewhat, but the frequencies remain approximately the same as in the search phase or drop slightly .
○ 6 . When the bat is within a few centimetres of the insect there is a terminal phase in which the pulse duration and interval between pulses shorten to about 0 . 5 millisecond and 5 or 6 milliseconds respectively . Contrary to a conclusion reached earlier on the basis of much less adequate data (Griffin, 1953), the frequency drops in the terminal phase, sometimes to 25 or 30 kilocycles . This is the buzz, which also occurs in many cases when the bat is dodging wires or landing.
○ 7 . The distance from the insect at which detection occurs can be judged by the shift from search to approach patterns . This distance of detection is commonly about 50 cm. for Drosophila, and it occasionally may be as much as a 153 metre with fruit flies or mosquitos.
8 . Two M. lucifugus which had become adept at catching Drosophila in the laboratory were exposed to broad band thermal noise either at low frequencies (0 . 1-15 kilocycles) or high (20- 100 kilocycles). The low frequency noise had an approximately uniform spectrum level of about 50 decibels per cycle band width (re 0 . 0002 dyne/cm2) from 0. 1 to 8 kilocycles . It was thus very loud compared to the flight sounds of Drosophila which have a fundamental frequency of a few hundred cycles/second and a maximum sound pressure level of 20-25 decibels at the distances of detection by these bats . The high frequency noise was of low and varying intensity, but it discouraged or prevented insect catching . The low frequency noise, on the other hand, had no effect on insect catching ; the bats gained weight in this noise (and in the dark) just as rapidly as in the quiet. Although bats sometimes detect insect prey by passive listening to sounds emanating from the insects themselves, these experiments appear to us to establish conclusively that small and relatively silent insects are often detected by echolocation .

21

Webster and Griffin (1962)

○ 1. A large series of electronic flash photographs of bats catching insects on the wing has demonstrated several common techniques employed
○ 2. A small and slow-flying insect such as a fruit fly may be sometimes seized directly with the mouth. In most cases, however, the interfemoral membrane is formed into a pouch by forward flexion of the hind legs and tail just before an insect is intercepted. Immediately after contact with the insect, the head is enclosed within the pouched tail membrane while the insect is seized in the jaws. Examples of this technique occur when a Myotis lucifugus catches mealworms tossed into the air, and when Lasiurus borealis catches flying moths.
○ 3. When the insect is not directly in front of the approaching bat one wing is often extended so as to intercept it. Sometimes the terminal joints of the 3rd and 4th fingers are flexed to form a scoop in which the insect is rapidly conveyed to the mouth, usually by way of the pouched tail membrane. This technique has been photographed in Myotis lucifugus catching fruit flies and also mealworms that had been tossed into the air. The wing was also employed in this manner during a single case where a greater horseshoe bat, Rhinolphus ferrum-equinum, was photographed catching a flying moth.
○ 4. In a few cases the photographs show that the wing is used either deliberately or accidentally to flick an insect into a position where it is seized in the mouth or pouched tail membrane a fraction of a second later. This technique has been clearly photographed only with Myotis lucifugus catching tossed mealworms.
○ 5. While the use of tail and wing membranes greatly increases the potential area of contact with insect prey over the area of the opened mouth alone, the photographs almost invariably show that the bat's head is pointed at the insect well before contact with it. Preparatory movements such as cupping the tail membrane, flexing the terminal joints of the fingers, and reaching the wing toward the moving insect, all show that the insect is located quite accurately before it touches any part of the bat. These photographs strongly indicate that each insect is individually located and intercepted.
6. The wing of these bats thus retains some of the prehensile functions of the hand in non-flying mammals.

22

How well can bats discriminate different sources? (Carew, 2005)

• Determining the limits of distance resolution (Simmons, 1973)
• Training: near platform contains reward, the far one not - sides swapped regularly
• Tests: sound-reflective targets removed from platforms and replaced with speakers - phantom targets presented via loudspeakers when pulse-echo delays modified and simulate smaller and smaller distanced between targets until choice perf breaks down (random choices around 50%)
- Train to find prey relative to something that I couldn't understand her saying
- See notes

23

How well can bats discriminate different sources? (Carew, 2005) research

Simmons (1973)

Schnitzler et al. (2003)

24

Simmons (1973)

Using simultaneous discrimination procedures the acuity of resolution of differences in target range has been determined on four species of echolocating bats (Eptesicus fuscus, Phyllostomus hastams, Pteronotus suapurensis, and Rhinolophus ferrumequinum ). All can discriminate range differences as small as 1 to 3 cm and, for the first three species, the acuity of range resolution appears to be independent of absolute range, at least at short distances. In Eptesicus range discrimination is mediated in terms of the arrival times of echoes returning from different targets. Comparisons between discrimination performance and autocorrelation functions of echolocation sounds used in the discriminations suggesthat these bats possess some neural equivalent of a matched-filter, ideal sonar receiver which functionally cross-correlates a replica of the outgoing signal with the returning echo to detect the echo and determine its arrival time. Eptesicus and Phyllostomus both use the entire FM signal for target ranging. Pteronoms uses its entire compound, short-duration CF/FM signal for ranging, while Rhinolophus separates the FM component from its compound, long-duration CF/FM sound and uses the FM part for target ranging. The results indicate different functions for the CF and FM components of bat sonar cries, and they suggest that the matched-filter or cross-correlation approach to echolocation is appropriate.

25

Schnitzler et al. (2003)

Field research on echolocation behavior in bats has emphasized studies of food acquisition, and the adaptive value of sonar signal design as been considered largely in the context of foraging. However, echolocation tasks related to spatial orientation also differ among bats and are relevant to understanding signal structure. Here, we argue that the evolution of echolocation in bats is characterized by two key innovations: first, the evolution of echolocation for spatial orientation and, second, a later transition for prey acquisition. This conceptual framework calls for a new view on field data from bats orienting and foraging in different types of habitats. According to the ecological constraints in which foraging bats operate, four distinct functional groups or guilds can be defined. Within each group, signal design and echolocation behavior are rather similar

26

Distance estimation from delay between pulse and echo (Simmons, 1971, 1973; Altringham, 1996; Carew, 2000)

see notes

• Smallest distance between targets can distinguish - how much echo is delayed after sound produced - delay between sound and echo returning to bat - equiv to distance range
• 20ms echo delay - short delay
- CF - range resolution not as good as those with many freqs

27

Distance estimation from delay between pulse and echo (Simmons, 1971, 1973; Altringham, 1996; Carew, 2000) research

Simmons et al. (2019)

28

Simmons et al. (2019)

In complex biosonar scenes, the delay of echoes represents the spatial distribution of objects in depth. To avoid overlap of echo streams from successive broadcasts, individual echolocation sounds should only be emitted after all echoes of previous sounds have returned. However, close proximity of obstacles demands rapid pulse updates for steering to avoid collisions, which often means emitting a new sound before all of the previous echoes have returned. When two echo streams overlap, there is ambiguity about assigning echoes to the corresponding broadcasts. In laboratory tests of flight in dense, cluttered scenes, four species of echolocating bats exhibited different patterns of pulse emissions to accommodate potential pulse-echo ambiguity. Miniopterus fuliginosus emitted individual FM pulses only after all echoes of previous pulses had returned, with no alternating between long and short intervals. Pipistrellus abramus and Eptesicus fuscus alternated between emitting long FM pulse intervals to receive all echoes before the next pulse, and short intervals to update the rapidly changing scene while accepting partial overlap of successive echo streams. Rhinolophus ferrumequinum nippon transmitted CF/FM pulses in alternating short and long intervals, usually two to four closely spaced sounds that produced overlapping echo streams, followed by a longer interval that separated echo streams. Rhinolophus f. nippon is a statistical outlier from the three FM species, which are more similar to each other. The repeated overlap of CF/FM echo streams suggests that CF components have a distinct role in rejection of clutter and mitigation of ambiguity.

29

Echolocation phases during an approach

• Myotis lucifugus (little brown bat) capturing a mealworm tossed into the air (Webster and Griffin, 1962)
• Species specific call
• Calls shorter over time and in faster succession - hone in on prey or coming closer to obstacle
• Active component/active control
- Can also go silent - eavesdrop on others - conceal what honing in on

see notes

- Heffner (2004)

see notes

• R'ship between max functional interaural distance (as measured by time in microseconds required for sound in air or water to travel from one auditory meatus to other) and high-freq hearing limit (highest freq audible at 60 dB SPL)
• Primates indicated by filled circles and named, along with some other fam species for comparison
• Stat analysis and regression line don’t include 3 subterranean species, indicated by triangles, for reasons described in text
• Regression line determined by minimising sum of square residuals
- Need to be small in size - small distance between ears

30

Echolocation phases during an approach research

Johnson et al. (2006)

Valero et al. (2017)