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Echolocation calls of rhinolophid and hipposiderid bats inSwazilandAuthor(s): Ara Monadjem, April Reside, Lindy LumsdenSource: South African Journal of Wildlife Research, 37(1):9-15. 2007.Published By: Southern African Wildlife Management AssociationDOI: http://dx.doi.org/10.3957/0379-4369-37.1.9URL: http://www.bioone.org/doi/full/10.3957/0379-4369-37.1.9

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Echolocation calls of rhinolophid andhipposiderid bats in Swaziland

Ara Monadjem1*, April Reside2 & Lindy Lumsden3

1All Out Africa Research Unit, Department of Biological Sciences, University of Swaziland, Private Bag 4, Kwaluseni, Swaziland2All Out Africa Research Unit, All Out, P.O. Box 132, Mahlanya, Swaziland

3Arthur Rylah Institute, Department of Sustainability and Environment, P.O. Box 137, Heidelberg, Victoria 3084, AustraliaReceived 16 September 2006. Accepted 14 November 2006

Echolocation call parameters of six species of rhinolophid and hipposiderid bat speciesoccurring in Swaziland are presented. All calls were obtained with the frequency-divisionANABAT bat detector, and mostly from hand-held individuals. There did not appear to be anydifferences in calls between hand-held and free-flying bats. However, there were significantinter-specific differences with respect to the constant frequency component of the call(equivalent to maximum frequency) and call duration. Minimum frequency was found to behighly variable, and considered not useful for species identification of free-flyingindividuals. Call parameters obtained in this study are very similar to those obtained with thetime-expansion Pettersson detector, suggesting that for this group, choice of detectormakes little difference. It is suggested that bat detectors provide an important method toinventory southern African bats, and supplement traditional, capture-based techniques,notably mist nets and harp traps.

Key words: echolocation, bat detector, ANABAT, Rhinolophidae, Hipposideridae, Swaziland.

INTRODUCTIONBats are notoriously difficult to capture, andchallenging to survey by conventional means.As aresult, bat distributions remain poorly known insouthern Africa compared to other small mammals(Monadjem 1998; Taylor 1998). However, with theadvent of affordable ultrasonic bat detectors, it hasbecome possible to describe the echolocationcalls of bats which have then been used to identifyfree-flying individuals (O’Farrell & Miller 1999;Russo & Jones 2002; Rydell et al. 2002).

Identification of bats to species level basedsolely on echolocation calls is complicated becausebats primarily utilize acoustic signals to perceivetheir environment, rather than as a species-specificmeans of communicating with mates as, for exam-ple, in birds (Barclay 1999). Acoustic signaturesoften vary intra-specifically (O’Farrell et al. 2000),leading to considerable overlap between species(Kingston et al. 1999). Despite this, echolocationcalls have successfully been used to identifyfree-flying bats in various studies conductedaround the world (O’Farrell 1997; O’Farrell et al.1999a; Duffy et al. 2000; Parsons 2001).

Acoustic signatures have been recorded anddescribed for a number of African bat species(Fenton et al. 1980; O’Shea & Vaughan 1980;

Fenton & Bell 1981; Fenton 1986; Aldridge &Rautenbach 1987; Taylor 1999). In a review ofsouthern African species, Taylor (1999) presentedecholocation call parameters for 36 species, rep-resenting just over half of the microchiropteransoccurring in the region. These calls were predomi-nantly recorded with a time-expansion Petters-son D980 bat detector, and its sonograms differsignificantly from those generated by frequency-division ANABAT bat detectors (Fenton et al.2001). Nonetheless, the ANABAT bat detector is auseful tool in the identification of free-flying bats(O’Farrell et al. 1999b; Duffy et al. 2000) and hasthe added advantage of being able to passivelyrecord calls in the absence of a human observer.This permits, inter alia, identification of speciespresent, monitoring of bat activity and observa-tions on community structure (Erickson & West2002). African bats that have been recorded withthe ANABAT bat detector include Chaerephonpumilus (Aspetsberger et al. 2003) and Miniopterusschreibersii (Jacobs 1999) in the families Molo-ssidae and Vespertilionidae, respectively.

Bats in the families Rhinolophidae and Hippo-sideridae typically emit calls with a constant fre-quency (CF) component, which tend to be of longduration (15–35 ms in southern African species;Taylor 2000) in the former group.CF bats also havea frequency modulated component which typically

South African Journal of Wildlife Research 37(1): 9–15 (April 2007)

*To whom correspondence should be addressed.E-mail: ara@uniswacc.uniswa.sz

involves a downward frequency sweep at the endof the CF component and a smaller upward sweepprior to it. Taylor (1999) provided echolocationcall parameters for seven rhinolophid and threehipposiderid species, of which only one (Rhinol-ophus darlingi) was recorded in Swaziland. Fourspecies of rhinolophids and two species ofhipposiderids have been recorded from Swaziland(Monadjem 1998; Monadjem 2005; Monadjemet al. 2005). The primary objective of this paper isto describe and compare ANABAT recordings ofthese six species for Swaziland populations.

METHODSBats were captured at a number of different loca-tions in Swaziland using standard mist nets and aharp trap (designed and manufactured by Austbat,Bairnsdale, Australia). The sex, mass and forearmlength (FL) were taken for all the individuals recordedin this study. Complete ossification of the fingerjoints in all subjects confirmed that they wereadults.Mensural data for voucher specimens of sixspecies of rhinolophids and hipposiderids, whichform the basis of this study, are presented withmuseum accession details (Table 1).

Echolocation calls were recorded from each indi-vidual. The majority of individuals were recorded

while being held by an observer. Hand-heldrecordings are generally not acceptable for lowduty cycle bats (Barclay 1999), but rhinolophidsand hipposiderids are high duty cycle species forwhich there is little difference in call structurebetween hand-held or free-flying situations,although free-flying bats do respond to Dopplershift by adjusting emitted frequencies to keepechoes at a fixed frequency (Pye 1972). Corrobo-rating this is the fact that there was little differencein call parameters between individuals of aspecies, even though for Rhinolophus clivosus, R.darlingi, R. simulator and Hipposideros caffer,some individuals were recorded on release orwhile flying in a room.

All recordings were made using an ANABAT IIbat detector (Titley Electronics, Ballina, Australia).Calls were analysed using ANALOOK software(Chris Corben, version 4.8, http://www.hoarybat.com). Only calls that were clearly defined wereanalysed.Parameters that were recorded includedthe frequency of the constant frequency (CF) com-ponent of the call, that equates to the maximumfrequency F(max), and duration. The minimumfrequency of the frequency modulated portion ofthe call F(min) in high duty cycle bats is highlyvariable and therefore not useful for identification

10 South African Journal of Wildlife Research Vol. 37, No. 1, April 2007

Table 1.Specimen details and body measurements of the rhinolophid and hipposiderid bats from which echolocationcalls were taken. DM: Durban Natural Science Museum; TM: Transvaal Museum.

Species Museum no. Sex Mass (g) FL (mm) Method

RhinolophidaeRhinolophus blasii DM7897 F 8.5 47.4 Hand-heldRhinolophus clivosus DM7894 M 12.4 53.0 Hand-heldR. clivosus DM8037 M 11.9 53.4 Hand-heldR.clivosus DM8047 M 12.7 53.6 Room-flownR. clivosus – M 18.0 53.5 Hand-heldR. clivosus – F 14.5 53.9 Hand-heldRhinolophus darlingi TM47742 M 8.3 46.3 Hand-heldR.darlingi TM47744 M 7.1 43.1 Hand-heldR.darlingi – M 8.9 46.0 ReleaseRhinolophus simulator DM7898 M 6.9 43.4 Hand-heldR. simulator DM7899 F 6.9 43.6 Hand-heldR. simulator DM8435 F 7.5 45.6 Room-flownHipposideridaeCloeotis percivali DM8026 M 4.0 33.8 Hand-heldC. percivali DM8027 F 4.0 34.2 Hand-heldHipposideros caffer DM7918 F 10.6 47.6 Hand-heldH. caffer DM7920 F 7.9 47.9 Hand-heldH. caffer DM8431 F 11.0 48.3 Hand-heldH. caffer – F 8.5 47.7 Hand-heldH. caffer – F 8.0 46.7 ReleaseH. caffer – F 11.0 47.5 ReleaseH. caffer – M 8.5 48.8 Release

purposes. Furthermore, there can be differentinterpretations as to the end point of the frequencymodulated component of the call, as the figurescalculated by ANALOOK and the minimumfrequencies as read from the sonogram, wereoften different (pers. obs.). For this reason, F(min)is not reported here.

RESULTSThe call parameters of rhinolophid and hipposideridbats from Swaziland are presented in Table 2, andan example of each is presented in Figs 1 & 2.There were significant differences between F(max)of the four Rhinolophus species (F = 17656.24,d.f. = 3,1045, P < 0.001; Tukey test, P < 0.05 for allpair-wise comparisons). Rhinolophus clivosuscalled at the highest F(max), whereas R. simulatorhad the lowest F(max). The calls of these twospecies did not overlap with any other species.Although R. darlingi and R. blasii called at signifi-cantly different frequencies this difference wasvery small; mean F(max) differed by just 0.6 kHz,and the range of F(max) overlapped. All theseRhinolophus species had medium to long callduration (20–38 ms) which differed significantly

between species (F = 538.95, d.f. = 3,1045, P <0.001; Tukey test, P < 0.05 for all pair-wise com-parisons). As found for F(max), the duration ofcalls of R. clivosus and R. simulator were distinct,but those of R. blasii and R. darlingi were moresimilar.

The F(max) for calls of Hipposideros caffer wasbetween about 140–146 kHz, while the mean forCloeotis percivali was 103 kHz. Call duration wasshort compared to the Rhinolophus: C. percivali(1.9 ms) and H. caffer (4.7 ms).

There were sufficient calls of males and femalesto allow a comparison between sexes for threespecies. Females of Rhinolophus clivosus, emitteda higher frequency call than males (t = 17.95, d.f. =430, P < 0.001) (Table 3). By contrast, males ofCloeotis percivali and Hipposideros caffer gavehigher frequency calls than females (t = 5.97 and2.59, d.f. = 122 and 86, P < 0.001 and P < 0.02 forC. percivali and H. caffer, respectively) (Table 3).

DISCUSSIONTo the best of our knowledge, these are the firstANABAT recordings of either rhinolophid orhipposiderid bats presented for southern Africa.

Monadjem et al.: Echolocation calls of rhinolophid and hipposiderid bats in Swaziland 11

Table 2. Echolocation call parameters (± standard deviation) of rhinolophid and hipposiderid bats from Swaziland.Frequencies (F) are quoted in kHz and duration in ms. The number of calls used in the analysis is presented as ‘N’.Numbers of individuals from which calls were extracted are presented in Table 1.

Species N F(max) Range of F(max) Duration

RhinolophidaeRhinolophus blasii 115 86.6 (± 0.23) 86.0–87.0 26.6 (± 3.9)R. clivosus 432 91.9 (± 0.65) 89.9–93.0 37.5 (± 8.0)R. darlingi 142 85.8 (± 0.36) 84.7–86.5 27.7 (± 4.4)R. simulator 360 84.1 (± 0.36) 82.1–84.7 20.8 (± 3.6)

HipposideridaeCloeotis percivali 124 103.4 (± 0.74) 101.6–105.3 1.9 (± 0.4)Hipposideros caffer 88 143.0 (± 1.43) 140.4–145.5 4.7 (± 1.1)

Table 3. Echolocation call parameters (± standard deviation) of male and female rhinolophid/hipposiderid bats fromSwaziland. Frequencies (F) are quoted in kHz. The number of calls used in the analysis is presented as ‘N’. Numbersof individuals from which calls were extracted are presented in Table 1.

Species N Sex F(max) Range of F(max) Duration

RhinolophidaeRhinolophus clivosus 147 F 92.5 (± 0.04) 92.5–93.0 37.5 (± 8.0)R. clivosus 285 M 91.6 (± 0.61) 89.9–93.0 35.7 (± 7.7)

HipposideridaeCloeotis percivali 34 F 102.9 (± 0.52) 102.2–104.2 1.9 (± 0.4)C. percivali 90 M 103.7 (± 0.71) 101.6–105.3 2.0 (± 0.5)Hipposideros caffer 85 F 142.9 (± 1.39) 140.4–145.5 4.7 (± 1.1)H. caffer 3 M 145.0 (± 0.76) 144.1–145.5 5.2 (± 0.4)

12 South African Journal of Wildlife Research Vol. 37, No. 1, April 2007

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The results of this study indicate that it is possibleto distinguish between the echolocation calls ofrhinolophid and hipposiderid species occurring inSwaziland. Rhinolophus clivosus, with F(max)about 92 kHz, called well above the frequency ofthe other three of the Rhinolophus species, whichranged between 82–87 kHz. R. simulator had thelowest F(max), which did not overlap with R. blasiior R.darlingi.The last two species had very similarF(max) that differed significantly by merely0.6 kHz. R. darlingi also had a significantly longercall. The slightly lower F(max), taken together withthe longer call duration should distinguish somefree-flying individuals of R. darlingi from R. blasii.Nevertheless, those represented in the overlapzone between these two species can only berecorded as a species complex. It should be notedthat recordings of only male R. darlingi and femaleR. blasii were obtained in this study. As a generalpattern, subject to available data, female Rhino-lophus typically emit a higher frequency call thanmales (Jones et al. 1992, 1993). Therefore, ahigher level of overlap should be expected in theF(max) of female R.darlingi and male R.blasii, andthese may be indistinguishable. Should this be thecase, it would pose a significant problem to theidentification of free-flying individuals of unknownsex. More calls of these two species are requiredto fully assess these differences.

The ANABAT calls presented here compare wellwith calls obtained from the time-expansionPettersson detector (Taylor 1999). The latter studypresented F(max) for R. clivosus, R. darlingi andR. simulator : 94.3, 86.2 and 82.7 kHz, respec-tively. For the last two species, these values over-lap with those presented in this study, whereas themean frequency of R. clivosus was just outside ofthe range reported in this study (89.9 kHz –93.0 kHz). However, it is important to emphasizethat recordings made with an ANABAT bat detec-tor should only be compared with other calls re-corded using the same make of bat detector. Thisunderscores the point that separate reference calllibraries need to be collected for different batdetectors.

Three Rhinolophus species have potentiallybeen overlooked in Swaziland, as they areknown in neighbouring parts of South Africa(Taylor 2000; Taylor et al. 2004; L. Cohen, pers.

Monadjem et al.: Echolocation calls of rhinolophid and hipposiderid bats in Swaziland 13

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comm.). Pettersson recordings of these threespecies indicate that they call at very differentF(max) to each other and to other Rhinolophusspecies: 40, 110 and 115 kHz for R. hildebrandtii,R. landeri and R. swinnyi, respectively (Aldridge &Rautenbach 1987; Taylor 1999). It is likely thatthese frequencies will be similar to those obtainedwith the ANABAT detector, and the presence ofthese bats in an area could be recorded by under-taking surveys using these detectors.

Hipposideros caffer calls at a frequency wellclear of other CF bats in southern Africa, andtherefore it should be identifiable with the use of abat detector. The F(max) range reported here(140–145 kHz) is identical to that obtained with aPettersson detector (Taylor 1999) and thereforethe choice of detectors should not make a differencefor the identification of this species. In contrast tothe rhinolophids, H. caffer and C. percivali malescalled at higher frequencies than females. Thehigher call frequency of female rhinolophids hasbeen correlated with their larger size in relation tothat of males (Jones et al. 1992). Yet in H. caffer,males tend to be slightly larger than females(Rautenbach 1981; Taylor 1998), possibly explain-ing this pattern. It is important to note that thesample sizes for the two hipposiderid species inthis study are small and may have contributed tothis difference. In the Indian H. speoris there is nosexual size dimorphism but males call at a higherfrequency than females (Jones et al. 1994).

Cloeotis percivali was recorded at a meanF(max) of 103 kHz, representing the fundamentalfrequency (Taylor 2000).This species is thought toprimarily use the first harmonic of 208–212 kHz(Fenton & Bell 1981; Taylor 2000); however, only asmall proportion of the calls in this study wererecorded at this frequency, with the majorityrecorded at the fundamental frequency. Whateverthe primary frequency used may be, this species isrecorded on the ANABAT system by a CF call ofaround 100–105 kHz. The very short call durationof this species should easily separate it fromrhinolophids calling around 110–115 kHz, whichhave call durations at least ten times longer.

The ability to distinguish southern African batsacoustically has significant consequences forthe design of small mammal surveys. Standardtechniques, such as the use of mist nets and harptraps, for inventorying bats is time-consuming andlabour-intensive, and maintenance costs are high(as nets need to be replaced regularly). Moreover,most taxa can be difficult to identify. The use of bat

detectors for surveying bats could at least supple-ment trapping techniques. The current study hasshown that it is possible to confidently identifyrhinolophid and hipposiderid species in Swazilandbased on their echolocation calls as recorded bythe ANABAT detector. It is important to note thatthis should not be interpreted as suggesting thattraditional survey methods be abandoned, nor thatthe collection of voucher specimens is no longernecessary. Many CF bats have high frequencycalls that attenuate over short distances. Hencethese calls do not carry far and the bat may need tobe within a couple of metres of the bat detector forit to be recorded. This reduces the detectability ofCF bats compared with, for example, bats from thefamilies Molossidae and Vespertilionidae that canbe recorded when flying at distances of up to 20metres (or more) from the recording device.Therefore, even at such a time that the calls ofall species have been adequately documented,taking into account geographical and individualvariation, acoustic recording should still go hand-in-hand with capture techniques.

ACKNOWLEDGEMENTSThis is the 6th Communication of the All Out

Africa Research Unit (www.all-out.org).We wish toexpress our sincere gratitude to the Director ofParks, Swaziland National Trust Commission, forgranting us access to Mlawula and MalolotjaNature Reserves. M. Reilly provided support atHlane National Park.

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Corresponding editor: M.I. Cherry