Search and hunting signals of echolocating European free-tailed bats, Tadarida teniotis, in southern Switzerland

Search and hunting signals of echolocating Europeanfree-tailed bats, Tadarida teniotis,

in southern Switzerland*

by K. ZBINDEN and P.E. ZINGG

University of Berne, Institute of Zoology, Department of Vertebrates,Hallerstr. 6, CH-3012 Berne, Switzerland

Summary. — Echolocation sounds of the bat Tadarida teniotis were recorded insouthern Switzerland. Bats hunting at low level over a village emitted single harmonic,narrowband FM-search pulses audible to the unaided ear. The signals covered a frequencyband from 15 kHz to 9 kHz. The frequency of the amplitude maximum (mean value= 11.4 kHz) and the end frequency of the sweep (mean value = 10.7 kHz) were foundto be useful for species identification in the field. The total signal duration varied from8 to 27 ms (mean value =15 ms). The average interval between search pulses was 740 ms.

On approaching prey, the sweep bandwidth of the signals was increased to 20 kHzand up to two more overlapping harmonics were introduced, increasing the overall band-width to more than 35 kHz. At the same time the modulation of the sweep was changedto linear period modulation. Intervals between pulses and pulse durations were reducedto end values of 7 and 2 ms respectively.

Flying in a laboratory room, a male T. teniotis emitted short multiple-harmonicFM-pulses with a bandwidth of more than 100 kHz.

The observed type of search pulse may be particularly suited for long range targetdetection, whereas approach pulses used when catching prey in the open, featuring alarge duration x bandwidth product, may facilitate exact prey location while maintaininga good sensitivity of the system.

Localities where T. teniotis has been found in Switzerland are referred to.

— Des signaux d'echolocation de Tadarida teniotis ont etc" enregistres dansle sud de la Suisse. Les molosses de Cestoni chassaient relativement bas au-dessus d'unvillage et emettaient des signaux de frequence modulee (FM) ä bände Stroke, qui consistaienten un seul harmonique. Ces signaux de detection etaient perceptibles pour Poreille humaine.Leur frequence se situait entre 15 et 9 kHz. La frequence instantanoe du signal au momentoii Samplitude passe par un maximum (moyenne = 11.4 kHz) et la frequence finale(moyenne = 10.7 kHz) du signal sont considerees comme valables pour Pidentificationacoustique du molosse sur le terrain. La duroe totale du signal variait entre 8 ms et

* By courtesy of V. Aellen, Museum of Geneva, this paper was presented in February1985 at the International C.N.R.S. colloquium "Air-borne Animal Sonar Systems" atLyon, France.

Mammalia, t. 50, n° 1, 1986.

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27 ms (moyenne = 15 ms). La moyenne des duroes qui separaient les signaux de detectionse situait ä 740 ms.

Au cours de Papproche de la proie, la bände frequentielle augmentait et atteignaitplus de 20 kHz. A ce moment les signaux montraient jusqu'ä trois harmoniques quise recouvraient partiellement et qui accroissaient la largeur totale de la bände de frequenceä plus de 35 kHz. Simultanement la modulation de periode suivait maintenant une loid'ällure lineaire. Les intervalles entre les signaux se raccourcissaient ä une valeur finalede 7 ms, et la duree des signaux diminuait jusqu'ä 2 ms dans la phase ultime de la capture.

Un molosse male qui volait dans un laboratoire emettait des signaux modules enfrequence avec plusieurs harmoniques et d'une duroe de 2-3 ms. La bände de frequencedopassait 100 kHz.

Les localitos oü Tadarida teniotis a ete trouvo en Suisse sont indiquees dans le texte.

INTRODUCTION

In Switzerland T. teniotis was recorded for the first time by Schneider (1871),who got a male bat from a house in Basle in October 1869. Up to the presentday this remains the only record of this species from the north side of theAlps. The second Swiss record was a pregnant female found in June 1872 nearthe hostel of St. Gotthard at 2000 m altitude (Fatio 1873, 1882). A skin, No.47.7.8.23 (Miller 1912) in the collection of the British Museum of Natural Historycarries a label with the indication "St. Gotthard. Purchased of Verreaux". "St.Gotthard" was crossed out later, as already mentioned by Aellen (1966) andthus remains uncertain.

Since 1958 the European free-tailed bat has been regularly caught at Colde Bretolet (1923 m altitude) by bird ringers and other naturalists (Aellen 1962,1966) and at Col de Balme, 2200 m altitude (Catzeflis 1980). In spring 1969O.v. Helversen observed flying . teniotis in the Maggia valley (District of Ticino)on several occasions (pers. comm.). Lehmann et al. (1981) discovered T. teniotisin the plain of Magadino in 1979, when they emerged from rocks and froma power line support and again in the Maggia valley in 1980.

We confirmed the presence of European free-tailed bats, flying out fromrocks, in the plain of Magadino (altitude 250 m) in 1983 and 1984. In 1984we observed several cruising bats in the Maggia valley (altitude 330-630 m).

Furthermore, we detected the same species in April 1984 over the footballfield in Bellinzona (altitude 230 m) and in the Centovalli (altitude 600 m), bothin the District of Ticino.

In September 1984 we found T. teniotis hunting in Castasegna (Val Bregaglia,altitude 720 m) at the border with Italy. T. teniotis thus appears to be muchmore common in southern regions of Switzerland (Fig. 1), than has been noticedso far.

Reviews of the world distribution of Tadarida teniotis have been given byAellen (1966) and Kock and Nader (1984).

Although echolocation signals of hunting T. teniotis are clearly audible tothe human ear, as described by Martens (1967), they had not yet been recordedon magnetic tape. The aim of this paper is to give a first description of theecholocation pulses of these bats hunting in open spaces. Further investigationwill be needed to reveal their full range of echolocation abilities under variouscircumstances.


ECHOLOCATING EUROPEAN FREE-TAILED BATS 11

Fig. 1. — Eight localities in southern Switzerland where T. teniotis has been found.Two further localities, Col de Bretolet and Col de Balme are not indicated on the map.

METHODS

High speed tape recordings of hunting Tadarida teniotis were made in Sou-thern Switzerland in the lower Valle Maggia (altitude 330 m) in spring 1984.Several bats were discovered hunting over a village area with a substantial propor-tion of green land covered with bushes and small trees. Both sides of the valleyare steep in this area and include numerous rocky sections, known to servethis species as roosting sites.

The bats were flying that evening at a rather low level, but still higherthan the street lights. Without night vision equipment available it was not possibleto observe their flight behaviour in detail during recording. In the course ofthe evening the local air temperature dropped from 12°C (21.45 h MEZ) to5°C (01.30 h MEZ) when the last bats were heard at the recording sites.

Two different recording sites, approx. 200 m from each other were chosenwithin the same village. Four tape reels were recorded on a Racal Store 4Dtape recorder at a tape speed of 30 ips (76 cm/s). Two channels were used fordata and one channel for commentary. The signals were picked up by a modifiedQMC S100 Ultrasound Detector with headstage and a second QMC SMI headstagewith power supply. Recording levels were continuously monitored with a portableTektronix dual channel oscilloscope and signal bandwidths were checked on sitewith a period meter.

Additional indoor recordings were made at the Natural History Museumin Basel with a B&K 1/8" condenser microphone type 4138 connected to aStellamaster Data Recorder with a frequency response to 150 kHz ( + /— 3 dB)at 30 ips. A single male bat was recorded when it left the hanging site and


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flew through a large room (10 χ 8 χ 3.5 m) at a height of about 1.5 m aboveground level.

In the laboratory all sections of good technical quality were slowed downeight times and copied onto a Sony TCD5 cassette recorder. A Nicolet type3091 dual channel digital oscilloscope (2 χ 4 k words) was used to display wave-forms and period plots. Intervals between pulses were measured from pulse centreto pulse centre. Pulse durations and sweep band widths were measured on thescreen, using the instrument together with a zero crossing detector (developedby D. Hartley, Queen Mary College, London and K. Zbinden, University ofBerne). The latter circuit can be switched to display period or logarithmic periodor frequency. A Kay type 6061 B sonagraph was used to illustrate selected sequen-ces. Power spectra of single pulses were measured with an FFT-analyser type2033 of B&K, Denmark.

RESULTS

Recorded signals included numerous trains of search pulses and several goodpursuit sequences. No 'social' calls were recognised. The bat's echolocation signalswere clearly audible to the unaided ear during most of the recording session.They were short, highpitched ticks which could easily be mistaken for shrewor cricket sounds by an unexperienced observer (See « Symbols » p. 24).

Search pulses were emitted in pulse trains with interpulse intervals varyingfrom about 200 ms to 1400 ms (Fig. 2). At both recording sites in the villagethe intervals were almost normally distributed about a mean value of 744 ms.

100 Frequency <n>

00

Frequency <n>

Interval <m1400

Interval <MS>

Fig. 2. — Histogram representation of intervals between search pulses. A : site 1 (N = 272,mean = 743 ms, sd = + /- 185 ms). B : site 2 (N = 286, mean = 744 ms,sd = +/- 154ms). Width of classes is 100ms.

In recording site 2 the statistical distribution of intervals was somewhat sharper(sd = +/- 154ms) than in site 1 (sd = +/- 185 ms). But apart from this,the signals recorded at the two sites did not appear to differ in any importantrespect and so they were put together for further analysis.

Total durations (T) of search pulses varied from about 8 ms to 27 ms ata mean value of 15 ms (Fig. 3 A). Shorter pulses were found only in pursuit



sequences. -6dB-durations (T-6dB) of the same search pulse sample ranged from4 to 23 ms with a mean value of 11.4ms (Fig. 3 B). The distributions show

B

Puls· Duration <«s> -6dB Duration (n

Fig. 3. — Histogram representation of duration of search pulses. A : total durationsin ms (N = 101, mean = 15.0ms, sd = +/- 3.7 ms). B : -6dB durations in ms(N = 101, mean = 11.4ms, sd = +/- 3.8ms). Width of classes is 1 ms.

*Ί*—if

70.60.

50.

40.

30.

20.

10.

—. 0

Frequency <n>

14 16Start Frequency (kHz)

mmife

Maxi mm Frequency <kHz>

50 Frequency <n>

End Frequency <kHz>

I?ig. 4. _ Histogram representation of three frequency parameters of search pulses. A :start frequency (N = 101, mean = 13.0kHz, sd = +/- 1.5 kHz). Β : frequencyof amplitude maximum, fmax (N = 101, mean = 11.6kHz, sd = +/- 1.0 kHz).C : end frequency (N = 101, mean = 10.7 kHz, sd = +/- 0.8 kHz). Width of clas-ses is 1 kHz.


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a few values that are almost double the mean values of pulse duration. Theyprobably represent signals from higher flying bats. These long pulses were nottypically preceded or followed by especially long intervals, however.

The start-frequency, the frequency of maximum amplitude and the end-frequency of the FM-sweep of the same search pulses were measured with theperiod meter to a resolution of -l·/-0.4 kHz. Their distribution is shown inFig. 4. All analysed search pulses were frequency modulated. The modulationrate varied from very shallow FM to moderately steep initial FM which alwaysended in shallow to very shallow FM (cf. Figs 6-8). No real CF-pulses werefound, although many pulses looked as if they were pure CF at first sight.The sweeps were checked with the zero crossing detector for linear period, linearfrequency and exponential frequency modulation. But none of the search pulsesshowed any of these distinct modulation laws. The sweeps started at an averagefrequency of 13 kHz and dropped through 11.6 kHz, where on average the ampli-tude maximum occurred, to an average end-frequency of 10.7 kHz. The startfrequency turned out to be the least reliable parameter. This was to be expected

10 Bandwidth (kHz)

* · · m *· m mm4 l«

· '«H β · II

10 15 20 25 30Total Duration (MS>

Fig. 5. — Sweep-bandwidth (BWsweep) of a sample of search pulses measured witha period meter plotted versus total pulse duration (T). Number of sample pulses N = 101.

from increased directivity and dispersion effects at high frequencies. Both thefrequency of the amplitude peak and the end frequency of the sweep were compa-ratively stable even with varying modulation rates. They may be taken as reliableparameters for determination of this species in the field. The signal bandwidth(BWsweep) was rather low compared with most other European FM-bats andvaried in the range of 0.4 to about 6 kHz at a mean value of 2.3 kHz (+ / — 1.1 kHzsd, N = 101). There was no clear relationship between bandwidth (as measuredhere) and duration of search pulses (Fig. 5). Fig. 6 represents a typical searchpulse of Tadarida teniotis. Figs 7 and 8 show the extremes with very shallowFM and steep FM respectively.

Two typical pursuit sequences (Tl and T2) will now be described in detail.




16 MAMMALIA

Tim· Cms)

Fig. 9. — Plots of intervals between pulses (including pulse durations) as a functionof time before prey capture for sequence Tl. A shows the full sequence from 9 sbefore interception (N = 44). B and C show the last part of the sequence at expandedtime scale (N = 30 and 28). In addition -6dB-pulse durations (T-6dB) are plotted.To obtain pulse duration in ms the values on the Y-axis are to be divided by 10.

Fig. 10. — As Fig. 9, but for sequence T2 (N = 33, 25 and 20).

600 Interval Cms)

Fig. 11. — Plots of intervals between pulses (including pulse durations) as a functionof time before prey capture. A-F are plots of the last section only of six differentsequences of approach (N = 15, 19, 20, 22, 28 and 29), in addition to Tl and T2.



kHz36 -

28 -I

20 -

12 -

4 -1689 m» 1089 m» 786 mt

44r-kHz

663 427 324 mt

kHz

28

20 v\253 196 150 100 50 Omt

Fig. 12. — Sonagram of sequence T2 (last 27 pulses), including oscillograms with superim-posed period plots (horizontal axis 3.35 ms/div.) of pulses out of different partsof the sequence. Filter bandwidth for the analysis was 2.4 kHz. Total sweep band-widths (BWsweep in period plot) were 3.8/14.4/17.6/9.4 kHz, sBW-6dB were0.3/3.9/5.6/3.9 kHz and fcs were 10.0/13.1/12.5/12.6 kHz for pulses No. 1/4/7/11of the sequence.


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Where appropriate, parameters of further sequences will be considered in addition.Figs 9 and 10 are plots of interpulse intervals over a period before detectionof prey and during pursuit down to the interception. Fig. 9 is for sequence Tl,Fig. 10 for sequence T2. Display A shows the whole sequence. In Tl the firstapparent reaction to the prey took place about 3 seconds before interception (').In seven pursuit sequences the time varied from 0.8-3 seconds. Assuming anaverage approach flight speed of 5 m/s, which is probably a rather low estimate,

-kHz362820124

203 140 104 60 Om·

24r-kHi

1646 m» 1216 r 841m»

32

24

i-kHz \\

596 432 317m·

32 P-kHz

\ ( \mi l l l l l l i i i i i i i in270 200 160 100 60 Om»

Fig. 13. — Sonagrams of sequence T3 (last 16 pulses) and sequence Tl (last 30 pulses ;scale magnifier on, upper frequency limit 32 kHz). Filter bandwidth was 2.4 and0.36 kHz.

(1) In T2 it probably took place about 2 seconds before interception.



the prey would have been detected at a range of at least 4 up to 15 meters.In search flight the intervals between pulses fluctuated considerably and irregularlyabout the mean value. When the approach phase started, the interval durationsdecreased with time at a varying rate probably depending on the flight pathof the prey .and the bat. In fact the rate varied quite a lot in different pursuitflights (cf. Fig. 11). So far it can only be stated that the change was rathernot a linear function of time to interception as we might have expected in thecase of a bat approaching the prey in a direct line. During the last 100-400 msbefore interception, the interval usually decreased at a low rate only (Figs 9C,IOC, 11). The pulse durations on the other hand decreased at an almost constantrate during the approach phase (Figs 9B, C and 10B, C).

The sonagram of T2 (Fig. 12) reveals a second and a third harmonic insome parts of the sequence. Judging from T3 (Fig. 13), which was a shortpursuit sequence of high amplitude, there may in fact always be several harmonicspresent from the late approach phase to the actual end of the terminal buzz.But since the buzz has a very low amplitude, parts of the buzz and certainlyhigher harmonics may usually be buried in noise when distant bats are recorded.When emitting sequence T3 the bat has probably been close to the microphoneand flying towards it.

When they were approaching a target, the bats increased the bandwidthof the FM-sweep at an increasing rate until it reached several times the original

Frequency (kHz)1412

10 15 20 25-6dB Duration (ms>

15 2Ό 25-6dB Duration Cms)

Fig. 14. — Plots of centre frequencies (fc) and -6dB-bandwidths (BW-6dB) as a functionof pulse duration (T-6dB) for sequence Tl (N = 30) and sequence T2 (N = 21).


20 MAMMALIA

search pulse bandwidth (Figs 12, 13 and 14). At the same time the centre frequency(fc) of the pulses (and their dominant frequency in the power spectrum) wasraised at a slowly decreasing rate. Then, as the sweep became shorter and shorter,the sweep bandwidth was reduced by reducing the start frequency and increasingthe end frequency simultaneously, whereas the overall bandwidth of the signalwas maintained by the introduced harmonics.

The modulation type changed from distinctly curved in the search and earlyapproach phase pulses to linear period modulation from about pulse No. 6 tothe end of the buzz in Tl and T2.

Fig. 15 is a plot of the -6dB duration χ bandwidth product for the sequencesTl (upper curve) and T2 (lower curve) against -6dB pulse duration. As in thecase of the search pulses, the product was not held constant. It increased steadilywith the first 5-6 pulses after the bat's first reaction having detected the preyto reach a maximum value when the pulse duration (T-6dB) had dropped toabout 10 ms. At this point the sweep bandwidth did not increase further andthe time-bandwidth product started to drop quite rapidly with decreasing pulseduration.

-6dB Duration * BW-6dB

60

50

40.

30.

20_

10

10 15 20 25-6dB Duration <ms>

Fig. 15. — Plots of time-bandwidth products (T-6dB χ BW-6dB) against T-6dB for sequen-ces Tl + T2 (Total number of pulses Ν = 52). Points are connected by a solidline for each sequence to show the change between successive pulses (sequences starton the right with long pulse durations).

Flying indoors in a large room, T. teniotis emitted a quite different typeof echolocation sound. It was a very broadband, multi-harmonic FM-pulse witha duration of only 2-3 ms. Five to seven harmonics were present in the signalsand overall bandwidth extended to well above 100 kHz. The bulk of the signalenergy was concentrated in the harmonics 2 and 3, i.e. a frequency band from25 to 60 kHz. Thus, compared with the signals emitted in open space, the signalenergy was transferred to much higher frequencies. The pulse duration was compa-rable to that obtained from pulses at the start of the final buzz (Fig. 16).

The pulse shown would support a very good range resolution in the orderof 0.8cm even under S/N-ratios of 1, if a semi-coherent receiver was beingused by the bat.



Fig. 16. — Oscillogram, sonagram and autocorrelation of a typical pulse emitted whenflying indoors in a laboratory room. The width of the envelope of the autocorrelationfunction at half power level (-3dB) indicates the range resolution estimated by asemi-coherent receiver at a S/N-ratio of 1.


22 MAMMALIA

DISCUSSION

The extraordinary flexibility of bats of the genus Tadarida in designing echo-location signals has been described in several papers (Simmons et al. 1978 ; Sim-mons et al. 1979 ; Simmons and Stein 1980 ; Fenton and Bell 1981). Soundtypes similar to those of T. teniotis were found by Simmons et al. (1978) inthe North American bat T. macrotis, whose search pulses sweep down to about35 kHz. Fenton and Bell (1981) reported end frequencies of 14-19 kHz in fiveTadarida species in Zimbabwe, Africa. T. teniotis thus appears to use the lowestfrequency search signals of all the bats in its group that have been investigated so far.

When searching for prey, T. teniotis emitted very narrowband signals oflong duration. These search signals are well suited for long range detection tasks,when analysed with any receiver type whose response does not deteriorate withdoppler shifts induced by relative movement of emitter and target. On the otherhand, when analysed with a narrow filter of fixed centre frequency (set to thefrequency of the emitted pulse) or when analysed with a semi-coherent receiver(for which the described search pulses have non-doppler tolerant properties),the same signals may be used to give a rough estimate of relative speed betweenemitter and target once the latter has been detected. Signal bandwidth may beat the lower extreme and sensitivity for target detection highest when the batsare flying at very high altitudes. High altitude flights of molossids have repeatedlybeen reported in the literature (Williams et al. 1973 ; Griffin and Thompson 1982).

In a noisy environment the search signals do not allow the separation ofvery closely spaced targets nor a very accurate measurement of the target position,however. At a S/N-ratio of 1 a -6dB-bandwidth (sBW-6dB) of 0.5-2 kHz limitsthe range resolution to 9-34 cm for this type of signal. But since the bats usethem at long range only, the resolution regarded as a percentage of total rangeis still quite good and could well reach the same magnitude as estimated forapproach pulses.

The observed search signals had a duration-bandwidth product of moderatemagnitude. When approaching prey, the bats almost doubled the T x BW product.A high Τ χ BW product may support either good sensitivity for relative velocitymeasurements or a good range resolution (Rihaczek 1977). Since in the presentcase the high T x BW product was due to a massive increase in signal bandwidth,the bat appears to have been using pulse compression techniques in order toimprove range resolution without losing system sensitivity. That sensitivity wouldhave decreased if the ranging precision had merely been improved by using evenshorter pulses instead. A typical pulse in this phase of the approach, at a sBW-6dBof about 5 kHz, has an estimated range resolution of approximately 3-4 cm.

At a very close range to the prey the Τ χ BW product dropped rapidlyagain, since both pulse duration and sweep bandwidth decreased. This of coursedecreased the energy content of the signal and the overall sensitivity of the system.But lower pulse energy is probably not critical at short range. At this stageof the approach harmonics were introduced, maintaining the overall bandwidthat a similar magnitude. Thus, range resolution was maintained by different meansto the end of the buzz. This way of retaining a high bandwidth has one drawback,however. Although the autocorrelation function (Ac) of such a signal will benarrower than the Ac of the same sweep without harmonics, secondary maxima



IT—-^\/\/^Fig. 17. — A set of 6 artificial, linear FM-sweeps with sine-wave envelopes and their

autocorrelation functions. Only the right half of each autocorrelation is shown. Thetime scale is identical for both waveform and correlation function. Note the foot-hillsand the higher power level of the main peak in the multi-harmonic sweeps.

will be introduced in the Ac (Figs. 16, 17). Thus, the bat may be able to maximizeranging precision by using this type of signal, but as a trade-off, the resolutionof the target in front of a reflective background would become difficult, becausethe foothills of the receiver output for the background could mask the weakermain peak indicating the target. This may not be important for a bat whichcommonly hunts in open spaces, however.

Apart from giving a good range resolution, due to its large bandwidth thissignal type is very well suited to recognition of objects and to discriminationbetween different textures. This signal property may actually be an importantreason for using the signal to identify prey in open space, as well as for echoloca-tion in a cluttered environment, such as the laboratory room described.

ACKNOWLEDGEMENTS

We wish to thank Mr. Frick and Mr. Galfetti for permitting use of the Racal recorderand the Department of Ethology, University of Berne, and Dr. O. Bernath, Departmentof Audiology of the Berne University Hospital, for permitting the use of their Sonagraphand FFT-analyser. We are indebted to Mr. J. Gebhard who provided a live bat forindoor recordings and to Mrs. C. Antognoli for assisting during the field recordings.We also thank J. David Pye for reading the manuscript and making helpful suggestionsfor its improvement. The research was supported by the Swiss National Science Foundation(grant no. 3.564.83).


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SYMBOLS

BWsweep : Total bandwidth of FM-sweep as measured with a period meter.BW-6dB : Sweep bandwidth between points of amplitude decay of -6dB from peak value

(period meter).sBW-6dB : -6dB power bandwidth as measured with an FFT-analyser.fmax : instantaneous freqency of amplitude maximum as measured with a period meter,fc : instantaneous frequency at the pulse centre (period plot, centre line between

-6dB amplitude points).fcs : frequency of centre line midway between -6dB points in the power spectrum,mean : statistical mean value of sample.N : total number of samples,sd : statistical standard deviation.T : total pulse duration.T-6dB : pulse duration between points of amplitude decay of -6dB from peak value.

BIBLIOGRAPHY

AELLEN, V., 1961. — Le baguement des chauves-souris au col de Bretolet (Valais). Arch.Sei. Gentve, 14: 365-392.

AELLEN, V., 1966. — Notes sur Tadarida teniotis (Raf.) (Mammalia, Chiroptera). I.Systematique, paleontologie et peuplement, repartition geographique. Rev. suisseZoo/., 73 : 119-159.

CATZEFLIS, F., 1980. — Apergu faunistique des micromammiferes de la vallee de Chamo-nix (Haute-Savoie). Arve-Loman-Savoie-Nature, No. 28 : 13-20.

FATIO, V., 1873. — Sur la presence en Suisse du Dysopes Cestonii (Savi). Act. Soc.helv. Sei. nat., 1872, Fribourg : 38-41.

FATIO, V., 1882. — Faune suisse. Additions aux Mammiföres. Faune des Vertebres dela Suisse, annexe au vol. 4, Geneve : 1 p.

FENTON, M.B., and G.P. BELL, 1981. — Recognition of species of insectivorous batsby their echolocation calls. J. Mamm.t 62 : 233-243.

GRIFFIN, D.R., and D. THOMPSON, 1982. — High altitude echolocation of insects bybats. Behav. Ecol. Sociobiol., 10 : 303-306.

KOCK, D., and I.A. NADER, 1984. — Tadarida teniotis (Rafinesque, 1814) in the W-Palaearctic and a lectotype for Dysopes rupelii Temminck, 1826 (Chiroptera :Molossidae). Z. Säugetierkunde, 49 : 129-135.

LEHMANN, R., H.P. STUTZ, and P. WIEDEMEIER, 1981. — Die Fledermäuse der KantoneZürich und Schwyz. Abschlussbericht der Arbeitsgruppe für Fledermausschutz zuhan-den der Pro Natura Helvetica. Zürich, Januar 1981. Polycopy, 127 pp.

MARTENS, J., 1967. — Plecotus austriacus (Fischer) auf Kreta ; mit Bemerkungen zuweiteren Arten (Mammalia, Chiroptera). Bonn. zool. Beitr., 18 : 253-257.

MILLER, G.S., 1912. — Catalogue of the Mammals of Western Europe (Europe exclusiveof Russia) in the collection of the British Museum. British Museum, London :xvi + 1019 pp.

RIHACZEK, A.W., 1977. — Principles of High-Resolution Radar. Mark Resources Inc.,Marina del Rey, California : 498 pp.

SCHNEIDER, G., 1871. — Dysopes Cestonii in Basel, eine für die Schweiz neue Fleder-maus. Beitrag zur Kenntnis dieser Art. N. Denkschr. Schweiz. Naturf. Ges., Zürich,24 : 1-9.



SIMMONS, J.A., M.B. FENTON, and M.J. OTARRELL, 1979. — Echolocation and thepursuit of prey by bats. Science, 203 : 16-21.

SIMMONS, J.A., W.A. LAVENDER et ai, 1978. — Echolocation by free-tailed bats (Tada-rida). J. Comp. PhysioL, 125 : 291-299.

SIMMONS, J.A., and R.A. STEIN, 1980. — Acoustic imaging in bat sonar : echolocationsignals and the evolution of echolocation. J. Comp. PhysioL, 135 : 61-84.

WILLIAMS, T.C., L.C. IRELAND, and J.M. WILLIAMS, 1973. — High altitude flights ofthe free-tailed bat, Tadarida brasiliensis, observed with radar. J. Mamm., 54 : 807-821.



Documents

Search and hunting signals of echolocating European free-tailed bats, Tadarida teniotis, in southern Switzerland