DOES BEAK SIZE AFFECT ACOUSTIC FREQUENCIES IN WOODCREEPERS?

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DOES BEAK SIZE AFFECT ACOUSTIC FREQUENCIES INWOODCREEPERSAuthor(s) Maria G Palacios and Pablo L TubaroSource The Condor 102(3)553-560 2000Published By Cooper Ornithological SocietyDOI httpdxdoiorg1016500010-5422(2000)102[0553DBSAAF]20CO2URL httpwwwbiooneorgdoifull1016500010-5422282000291025B05533ADBSAAF5D20CO3B2

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[553]

The Condor 102553ndash560q The Cooper Ornithological Society 2000

DOES BEAK SIZE AFFECT ACOUSTIC FREQUENCIESIN WOODCREEPERS1

MARIA G PALACIOSLaboratorio de Vertebrados Departamento de Ciencias Biologicas Facultad de Ciencias Exactas y

Naturales Universidad de Buenos Aires Buenos Aires Argentina

PABLO L TUBARO2

Division Ornitologıa Museo Argentino de Ciencias Naturales lsquolsquoBernardino Rivadaviarsquorsquo Av Angel Gallardo470 1405mdashBuenos Aires Argentina e-mail ptubaroproteusdnaubaar

Abstract We assessed the effect of beak morphology on the acoustic structure of wood-creeper (subfamily Dendrocolaptinae) songs using a comparative analysis of independentcontrasts For the song of each species we measured the maximum and minimum frequen-cies the bandwidth and the emphasized frequency Residuals of variation in beak lengthand acoustic frequencies after controlling for body size and phylogeny were calculated foreach species and compared We found a negative relationship between the residuals ofacoustic frequencies and the residuals of beak length This relationship was significant foremphasized frequency when we excluded two open-habitat species Scimitar-billed Wood-creeper (Drymornis bridgesii) and Narrow-billed Woodcreeper (Lepidocolaptes angustiros-tris) This result is consistent with the hypothesis that the suprasyringeal vocal tract hasresonating properties that affect the frequency spectrum of the song

Key words beak length body size Dendrocolaptinae resonance song structure wood-creepers

INTRODUCTION

Recent studies have shown that the suprasyrin-geal vocal tract can affect the frequency spec-trum of avian vocalizations Nowicki (1987)showed that some songbird species singing in anhelium-enriched and nitrogen-depleted atmo-sphere had a harmonic structure normally ab-sent suggesting that vocal tract resonances filterout most of the spectral structure of the signalIn the Barnacle Goose (Branta leucopsis) thoseindividuals that vocalize with their bills wideopen emphasize higher frequencies (Hausbergeret al 1991) Westneat et al (1993) in a studyof White-throated Sparrows (Zonotrichia albi-collis) and Swamp Sparrows (Melospiza geor-giana) found that the acoustic frequencies ofnotes in a song have a positive correlation withbeak gape in both species In addition in SongSparrow (Melospiza melodia) changes in beakgape during vocal ontogeny appear to corre-spond with the development of tonal quality ofsong (Podos et al 1995) One possible expla-nation for these observations is that changes inbeak gape influence the tonal quality of song bydynamically modifying the vocal tractrsquos reso-

1 Received 17 June 1999 Accepted 29 February2000

2 Corresponding author

nance properties (Nowicki 1987 Nowicki andMarler 1988 Gaunt and Nowicki 1998)

Based on this evidence that the resonance ofthe vocal tract affects the spectral structure ofsong we predicted that the acoustic frequenciescontained in avian song will be negatively re-lated to beak length across species all other fac-tors being equal We tested this prediction usinga comparative analysis of the spectral structureof the song in woodcreepers (Dendrocolaptinae)We chose to use this monophyletic group en-demic to the Neotropics because bill lengthvaries enormously ranging from 12 mm in thegenus Glyphorhinchus to 76 mm in the genusNasica In addition there is a cladistic phylog-eny for the group (Raikow 1994) and song re-cordings of almost all the species (Hardy et al1995) Several studies have demonstrated a neg-ative relationship between acoustic frequenciesand body size (Wallschlager 1980 Ryan andBrenowitz 1985 Tubaro and Mahler 1998) it isreasonable to assume that beak size correlateswith body size and phylogeny as well To studythe relationship between beak morphology andthe acoustic frequencies of song it is importantto remove the confounding effect of body sizeand phylogeny Thus we present the results ofthe analyses between the residuals of variationin bill length and acoustic frequencies after con-

554 MARIA G PALACIOS AND PABLO L TUBARO

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BEAK SIZE AND SONG STRUCTURE 555

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trolling for the effect of body size and phylog-eny

METHODS

The present analyses of woodcreeper song werebased on recordings published by Hardy et al(1995) representing songs of 46 out of 50 spe-cies Sonograms for the song of each recordedspecies were made with a Proaudio Spectrum 16Sound Blaster (Media Vision Freemont Cali-fornia) and Canary v12 software (Charif et al1995) On each sonogram we measured the fol-lowing variables maximum and minimum fre-quencies (MAX and MIN respectively) band-width (BAND 5 MAX 2 MIN) and empha-sized frequency (frequency with the highest am-plitude in the song ENF see Table 1) Allmeasurements were made by an assistant whoknew neither the beak length nor the body massof the species under study Body mass data wereobtained from Dunning (1993) Sources con-sulted for speciesrsquo bill lengths were von Ihering(1899) Dabbene (1912) Sneathlage (1914)Chapman (1917) Cory and Hellmayr (1925)Gyldenstolpe (1945a 1945b) Esteban (1948)Wetmore (1972) Phelps and Meyer de Schauen-see (1978) Fjeldsa and Krabbe (1990) Dubs(1992) and Ridgely and Tudor (1994) Beaklengths of Drymornis bridgesii and Lepidoco-laptes squamatus males were measured on studyskins deposited at the Museo Argentino de Cien-cias Naturales Bernardino Rivadavia We couldnot find information about the bill lengths ofLepidocolaptes leucogaster Xiphorhynchus er-ythropygius and X flavigaster therefore thesespecies were deleted from some comparativetests but still considered in the estimation of therelationship between body mass and acousticfrequencies of the song Common names of spe-cies are given in Table 1

We based our phylogenetic analysis on thecladistic hypothesis of Raikow (1994) This hy-pothesis is not based on the acoustic structure ofthe song but on the morphological characters of39 species of woodcreepers We estimated theancestral states of the characters using the punc-tuated model (Harvey and Purvis 1991) that as-sumes that changes occur only at the nodes of atree Details of the general procedure for esti-mating the ancestral character values are out-lined in Felsenstein (1985) Finally we made thenondirectional comparative tests using the in-dependent contrasts method (Felsenstein 1985)

and the CAIC software v20 (Purvis and Ram-baut 1995)

Briefly the independent contrasts method isbased on the comparison between pairs of sisterspecies Each comparison produces a new vari-able termed a lsquolsquocontrastrsquorsquo which results from thedifference between the values of the variablemeasured on the species within the pair Con-trasts may be standardized if divided by thesquare root of the length of the branches undercomparison These contrasts are considered in-dependent among pairs of sister species becausethey result from the evolutionary divergence thatoccurred after the origin of each pair Homoge-neity of variance of standardized contrasts wasconfirmed using the method proposed by Purvisand Rambaut (1995) Thus any association be-tween standardized contrasts belonging to dif-ferent variables may be detected using a stan-dard linear regression model adjusted to passthrough zero (Grafen 1989 Garland et al 1992)This is because the expected value in the depen-dent variable contrast must be zero when the in-dependent variable contrast is zero In comput-ing comparative analyses polytomies (iepoints in the phylogeny with more than two de-rived branches simultaneously) were resolved bythe method of Pagel (1992)

To assess the effect of beak length on acousticfrequencies of the song it is important to controlfor all other sources of variation in the signalIn addition to body size the habitat used by thespecies may affect the spectral structure of thesong employed for long-range communication(Morton 1975 Wiley 1991) Although wood-creepers comprise a uniform group of mainlyhumid and montane forest species that forage ontree trunks well above the ground two excep-tions to this pattern are Drymornis bridgesii andLepidocolaptes angustirostris which live in aridlowland scrub and chaco-cerrado habitats (Rid-gely and Tudor 1994 Parker et al 1996) Forthis reason we repeated the comparative analy-ses with and without these species included inthe data matrix All statistical tests were per-formed on the log-transformed values of theoriginal variables

RESULTS

Independent contrast analysis revealed that beaklength correlates positively with body mass (b5 045 F120 5 52 P 003) In additionacoustic frequencies varied negatively with body


TABLE 2 Regressions of phylogenetically indepen-dent contrasts in acoustic frequencies with contrasts inbody mass All original variables were log-trans-formed For acronyms see Methods

Comparisons ba F P

Excluding D bridgesii and L angustirostris (df 5 122)

MAX with body mass 2041 45 005MIN with body mass 2040 43 005BAND with body mass 2035 30 010ENF with body mass 2054 89 001

Including D bridgesii and L angustirostris (df 5 124)


a Slope of the regression forced to pass through zero

TABLE 3 Regressions of phylogenetically indepen-dent contrasts in residuals of acoustic frequencies withcontrasts in residuals of beak length For acronyms seeMethods

Comparisons ba F P


MAX with beak length 2023 11 030MIN with beak length 2030 20 017BAND with beak length 2014 04 053ENF with beak length 2042 44 005




mass although this relationship was significantfor MAX MIN and ENF but not for BAND(Table 2) The inclusion of both D bridgesii andL angustirostris in the analysis reduced the sta-tistical significance of the regression slopes ofMAX and MIN in relation to body mass al-though the relationship between ENF and bodymass was still significant (Table 2) To avoid theconfounding effect of body mass differences incomparisons involving other variables we cal-culated residuals of variation using the slope ofthe regression (forced to pass through zero)among their respective contrasts and body masscontrasts (Garland et al 1992) Thus residualsof variation in acoustic frequencies were com-pared with residuals in beak length but control-ling again for phylogeny We found a negativerelationship between both sets of residuals No-tably the slope of the regression between con-trasts in ENF and beak length was negative andsignificant (Table 3) In other words within eachcompared pair of forest species the species withthe longest beak had the lowest emphasized fre-quencies in its song However this relationshipwas not significant when D bridgesii and L an-gustirostris were included in the analysis (Table3)

DISCUSSION

These data represent the first comparative studyof the relationship between bill length and thespectrum of frequencies contained in the song ofa diverse group of Neotropical passerines Re-siduals of acoustic frequencies and beak length

were negatively correlated indicating that thelonger the beak the lower the acoustic frequen-cies of the song This pattern is present withinthe group of woodcreepers living in humid for-ests even after accounting for the effect of in-terspecific differences in body mass and phylog-eny When the species living in more xeric andopen-country habitats were included in the anal-yses the statistical significance of the relation-ship was lost This lack of significance is mainlybecause the song of D bridgesii contained high-er frequencies than expected based on its bodysize and beak length We think that such a pat-tern could be related to the specialized open-country and ground foraging habits of this prim-itive species In general studies of passerinespecies living in open habitats have shown thatthey have higher frequencies and wider band-widths than their counterparts from more closedhabitats (Morton 1975 Wiley 1991)

The existence of a negative relationship be-tween residuals of beak length and emphasizedfrequency is compatible with the idea that thesuprasyringeal vocal tract has resonating prop-erties that affect the frequency spectrum of thesong (Nowicki 1987 Nowicki and Marler 1988Gaunt and Nowicki 1998) Length of the tubeformed by the trachea and buccal cavities chang-es with beak aperture If species use a similarbill gape at the tip this implies that the anglebetween upper and lower mandibles is propor-tionally smaller for the species with a longerbeak In this way a longer beak adds propor-tionately more to the length of the orotracheal


cavity compared to a short beak reducing itsresonating frequency

It is interesting to note that if species werenot constrained in their angle of beak aperturespecies with longer beaks could produce maxi-mum frequencies as high as shorter-beak spe-cies Moreover they could produce wider band-width songs depending on the degree of changein beak aperture during singing This is becausefor the same range of angular apertures of thebeak at the base longer-beaked species producea wider variation in the length of the resonatingtube We found no evidence of longer-beakedspecies singing wider bandwidth songs thantheir shorter-beaked counterparts In contrast re-siduals of beak length correlated negatively withresiduals of BAND although this relationshipwas not significant However a correct test ofthis prediction requires the comparison of songbandwidth of video-recorded birds during sing-ing so as to assess their degree of beak aperture

There are strong differences in beak curvatureamong woodcreepers ranging from the genusCampylorhamphus with its strongly decurvedbeak to the genera Sittasomus or Dendrocinclawith their straight beaks Curvature of the beakcould affect the relationships between songstructure and beak length in at least two differentways First beak length usually is measured dor-sally as the chord from the tip to the base (Bald-win et al 1931) However the acoustically ef-fective length of a beak is the one which deter-mines its resonance properties when modeled asa hollow tube For a curved beak this effectivelength is better estimated as a geometric arc be-cause the use of chord length instead of its arcsystematically underestimates the effectivelength of a curved beak relative to a straight oneSecond strongly curved beaks exhibit a reducedand more uniform gape rostral to the bend whenthe jaws are open (Olson and Feduccia 1980)thus affecting the effective length of the reso-nating tube as well as its properties as an im-pedance matching device

Greenewalt (1968) compared the tracheallength of several bird species and their songsand concluded that there was no relationship be-tween them Furthermore he found no evidencefor resonances and antiresonances in continuousmodulated notes covering a wide range of fre-quencies These observations indicate why clas-sical models of sound production proposed thatspectral properties were determined at the source

(ie oscillating membranes of the syrinx) withno appreciable effect of suprasyringeal tract(Brackenbury 1982 Gaunt and Gaunt 1985Gaunt and Nowicki 1998)

More recent studies of birds singing in a lessdense atmospheric condition largely composedof helium instead of nitrogen (ie lsquolsquohelioxrsquorsquo at-mosphere) indicated that the suprasyringeal vo-cal tract could indeed affect the acoustic spec-trum of the sound (Nowicki 1987) Becauseacoustic resonance depends on sound wave-length which increases in a heliox atmospherethe frequency of resonance of the vocal tract isshifted upwards This change should be reflectedin a concomitant drop in the amplitude of thefundamental frequency because it will now lieoutside of the resonance peak of the vocal tractIn addition the finding of the presence of anyovertone could indicate that the vocal tract hasfiltered that band in the normal song Nowicki(1987) found evidence for both phenomena in atleast 10 species of songbirds Another study inBudgerigars (Melopsittacus undulatus) showedno evidence of suprasyringeal tract resonance(Brittan-Powell et al 1997) demonstrating thatdifferent species could use different mechanismsof sound production Even within the same spe-cies steady and modulated frequency notes maydiffer as to whether or not vocal tract resonancesare involved in the sound production mechanism(Ballintijn and Ten Cate 1998)

Finally it is important to note that informationabout within-individual inter-individual andgeographical variation of songs also are requiredto assess whether song samples included in thisstudy are representative of the species HoweverMarantz (1992) suggests that variation in wood-creeper vocalizations parallels that of membersof the related families Tyrannidae and Formi-cariidae in that advertising song varies little overlarge geographic distances and generally lacksboth dialects and repertoires He also found ahigh degree of conservatism in the temporalstructure of song among genera as well as withinthe genus Dendrocolaptes Even for Dendroco-laptes certhia a species showing geographicalvariation in song differences are reflected intiming and note shape rather than overall fre-quency

ACKNOWLEDGMENTS

We thank J Hardy T Parker and B Coffey for thepublished recordings of the voices of the woodcree-


pers as well as to the persons that contributed to thatwork We also thank J Navas who made available thecollections of the Museo Argentino de Ciencias Na-turales Curtis Marantz for sharing with us his knowl-edge about woodcreepers S Lougheed for improvingthe English of the manuscript and two anonymous re-viewers for their interesting comments and sugges-tions This work was supported by the Consejo Na-cional de Investigaciones Cientıficas y Tecnicas theAgencia Nacional de Promocion Cientıfica y Tecnol-ogica (PICT 97mdashBID OCAR 00322) and the Uni-versity of Buenos Aires Argentina (UBACyT PS-021T)

LITERATURE CITED

BALDWIN S P H C OBERHOLSER AND L G WORLEY1931 Measurements of birds Sci Publ Cleve-land Mus Nat Hist 21ndash165

BALLINTIJN M R AND C TEN CATE 1998 Soundproduction in the collared dove a test of thelsquowhistlersquo hypothesis J Exp Biol 2011637ndash1649

BRACKENBURY J H 1982 The structural basis of voiceproduction and its relation to sound characteris-tics p 53ndash73 In D E Kroodsma E H Millerand H Ouellet [EDS] Acoustic communication inbirds Vol 1 Academic Press New York

BRITTAN-POWEL E F R F DOOLING O N LARSENAND J T HEATON 1997 Mechanisms of vocalproduction in budgerigars (Melopsittacus undula-tus) J Acoust Soc Am 101578ndash589

CHAPMAN F M 1917 Distribution of bird-life in Co-lombia Bull Am Mus Nat Hist 361ndash729

CHARIF R A S MITCHELL AND C W CLARK 1995Canary 12 userrsquos manual Cornell Laboratory ofOrnithology Ithaca NY

CORY C B AND E HELLMAYR 1925 Catalogue ofthe birds of the Americas Part IV FurnariidaemdashDendrocolaptidae Field Mus Nat Hist (Zoolog-ical Series) 131ndash390

DABBENE R 1912 Contribucion a la ornitologıa delParaguay Anales del Museo Nacional de HistoriaNatural de Buenos Aires 23283ndash390

DUBS B 1992 Birds of southwestern Brazil catalogueand guide to the birds of the Pantanal and MatoGrosso and its border areas Betrona-Verlag Kus-nacht Switzerland

DUNNING J B JR 1993 CRC handbook of avianbody masses CRC Press Boca Raton FL

ESTEBAN J G 1948 Contribucion al conocimiento delos Dendrocolaptidos argentinos Acta ZoologicaLilloana 5325ndash436

FELSENSTEIN J 1985 Phylogenies and the comparativemethod Am Nat 1251ndash15

FJELDSA J AND N KRABBE 1990 Birds of the HighAndes Zoological Mus Univ CopenhagenSvendborg Denmark

GARLAND T P H HARVEY AND A R IVES 1992Procedures for the analysis of comparative datausing phylogenetically independent contrastsSyst Biol 4118ndash32

GAUNT A S AND S L L GAUNT 1985 Syringealstructure and avian phonation Current Ornithol2213ndash245

GAUNT A S AND S NOWICKI 1998 Sound produc-tion in birds acoustics and physiology revisitedp 291ndash321 In S L Hopp M J Owren and CS Evans [EDS] Animal acoustic communicationSpringer Berlin

GRAFEN A 1989 The phylogenetic regression PhilTrans R Soc Lond 326119ndash156

GREENEWALT C H 1968 Bird song acoustics andphysiology Smithson Inst Press WashingtonDC

GYLDENSTOLPE N 1945a A contribution to the orni-thology of northern Bolivia K Sven Vetenskap-sakad Handl Ser 3 231ndash300

GYLDENSTOLPE N 1945b The bird fauna of Rio Juruain western Brazil K Sven VetenskapsakadHandl Ser 3 221ndash338

HARDY J W T A PARKER AND B B COFFEY 1995Voices of the woodcreepers 2nd ed Ara RecordsGainesville FL

HARVEY P H AND A PURVIS 1991 Comparativemethods for explaining adaptations Nature 351619ndash624

HAUSBERGER M J M BLACK AND J P RICHARD1991 Bill opening and sound spectrum in barna-cle goose loud calls individuals with lsquowidemouthsrsquo have higher pitched voices Anim Behav42319ndash322

MARANTZ C A 1992 Evolutionary implications ofvocal and morphological variation in the wood-creeper genus Dendrocolaptes (Aves Dendroco-laptidae) MSc thesis Louisiana State Univ Ba-ton Rouge LA

MORTON E S 1975 Ecological sources of selectionon avian sounds Am Nat 10917ndash34

NOWICKI S 1987 Vocal tract resonances in oscine birdsound production evidence from bird songs in ahelium atmosphere Nature 32553ndash55

NOWICKI S AND P MARLER 1988 How do birds singMusic Percep 5391ndash426

OLSON S L AND A FEDUCCIA 1980 Relationshipsand evolution of flamingos (Aves Phoenicopteri-dae) Smithson Contrib Zool 3161ndash73

PAGEL M D 1992 A method for the analysis of com-parative data J theor Biol 156431ndash442

PARKER T A III D F STOTZ AND J W FITZPATRICK1996 Ecological and distributional databases p131ndash291 In D F Stotz J W Fitzpatrick T AParker III and D K Moskovits [EDS] Neotropi-cal birds ecology and conservation Univ Chi-cago Press Chicago

PHELPS W H AND R MEYER DE SCHAUENSEE 1978A guide to the birds of Venezuela Princeton UnivPress Princeton NJ

PODOS J J K SHERER S PETERS AND S NOWICKI1995 Ontogeny of vocal tract movements duringsong production in song sparrows Anim Behav501287ndash1296

PURVIS A AND A RAMBAUT 1995 Comparative anal-ysis by independent contrasts (CAIC) an AppleMacintosh application for analyzing comparativedata Computer Appl Biosciences 11247ndash251

RAIKOW R J 1994 A phylogeny of the woodcreepers(Dendrocolaptinae) Condor 111104ndash114

RIDGELY R S AND G TUDOR 1994 The birds of


South America Vol II Univ Texas Press AustinTX

RYAN M J AND E A BRENOWITZ 1985 The role ofbody size phylogeny and ambient noise in theevolution of bird song Am Nat 12687ndash100

SNEATHLAGE E 1914 Catalogo das aves amazonicasBoletim do Museu Goerdi 81ndash530

TUBARO P L AND B MAHLER 1998 Acoustic fre-quencies and body mass in New World dovesCondor 10054ndash61

VON IHERING H 1899 As aves do estado de S PauloDa revista do Museu Paulista 3113ndash476

WALLSCHLAGER D 1980 Correlation of song frequen-

cy and body weight in passerine birds Experientia36412

WESTNEAT M W J H LONG W HOESE AND S NOW-ICKI 1993 Kinematics of birdsong functionalcorrelation of cranial movements and acoustic fea-tures in sparrows J Exp Biol 182147ndash171

WETMORE A 1972 The birds of the Republic of Pan-ama Part 3 Passeriformes Dendrocolaptidae toOxyruncidae Smithson Inst Press WashingtonDC

WILEY R H 1991 Associations of song propertieswith habitats for territorial oscine birds of easternNorth America Am Nat 138973ndash993

[553]

The Condor 102553ndash560q The Cooper Ornithological Society 2000

DOES BEAK SIZE AFFECT ACOUSTIC FREQUENCIESIN WOODCREEPERS1

MARIA G PALACIOSLaboratorio de Vertebrados Departamento de Ciencias Biologicas Facultad de Ciencias Exactas y

Naturales Universidad de Buenos Aires Buenos Aires Argentina

PABLO L TUBARO2

Division Ornitologıa Museo Argentino de Ciencias Naturales lsquolsquoBernardino Rivadaviarsquorsquo Av Angel Gallardo470 1405mdashBuenos Aires Argentina e-mail ptubaroproteusdnaubaar

Abstract We assessed the effect of beak morphology on the acoustic structure of wood-creeper (subfamily Dendrocolaptinae) songs using a comparative analysis of independentcontrasts For the song of each species we measured the maximum and minimum frequen-cies the bandwidth and the emphasized frequency Residuals of variation in beak lengthand acoustic frequencies after controlling for body size and phylogeny were calculated foreach species and compared We found a negative relationship between the residuals ofacoustic frequencies and the residuals of beak length This relationship was significant foremphasized frequency when we excluded two open-habitat species Scimitar-billed Wood-creeper (Drymornis bridgesii) and Narrow-billed Woodcreeper (Lepidocolaptes angustiros-tris) This result is consistent with the hypothesis that the suprasyringeal vocal tract hasresonating properties that affect the frequency spectrum of the song

Key words beak length body size Dendrocolaptinae resonance song structure wood-creepers

INTRODUCTION

Recent studies have shown that the suprasyrin-geal vocal tract can affect the frequency spec-trum of avian vocalizations Nowicki (1987)showed that some songbird species singing in anhelium-enriched and nitrogen-depleted atmo-sphere had a harmonic structure normally ab-sent suggesting that vocal tract resonances filterout most of the spectral structure of the signalIn the Barnacle Goose (Branta leucopsis) thoseindividuals that vocalize with their bills wideopen emphasize higher frequencies (Hausbergeret al 1991) Westneat et al (1993) in a studyof White-throated Sparrows (Zonotrichia albi-collis) and Swamp Sparrows (Melospiza geor-giana) found that the acoustic frequencies ofnotes in a song have a positive correlation withbeak gape in both species In addition in SongSparrow (Melospiza melodia) changes in beakgape during vocal ontogeny appear to corre-spond with the development of tonal quality ofsong (Podos et al 1995) One possible expla-nation for these observations is that changes inbeak gape influence the tonal quality of song bydynamically modifying the vocal tractrsquos reso-

1 Received 17 June 1999 Accepted 29 February2000

2 Corresponding author

nance properties (Nowicki 1987 Nowicki andMarler 1988 Gaunt and Nowicki 1998)

Based on this evidence that the resonance ofthe vocal tract affects the spectral structure ofsong we predicted that the acoustic frequenciescontained in avian song will be negatively re-lated to beak length across species all other fac-tors being equal We tested this prediction usinga comparative analysis of the spectral structureof the song in woodcreepers (Dendrocolaptinae)We chose to use this monophyletic group en-demic to the Neotropics because bill lengthvaries enormously ranging from 12 mm in thegenus Glyphorhinchus to 76 mm in the genusNasica In addition there is a cladistic phylog-eny for the group (Raikow 1994) and song re-cordings of almost all the species (Hardy et al1995) Several studies have demonstrated a neg-ative relationship between acoustic frequenciesand body size (Wallschlager 1980 Ryan andBrenowitz 1985 Tubaro and Mahler 1998) it isreasonable to assume that beak size correlateswith body size and phylogeny as well To studythe relationship between beak morphology andthe acoustic frequencies of song it is importantto remove the confounding effect of body sizeand phylogeny Thus we present the results ofthe analyses between the residuals of variationin bill length and acoustic frequencies after con-


TA

BL

E1

Dat

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edin

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tive

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ysis

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For

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ds

Spe

cies

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Spe

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Thi

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(las

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onan

cest

orof

all

the

spec

ies)



METHODS






RESULTS




Comparisons ba F P







Comparisons ba F P







DISCUSSION












ACKNOWLEDGMENTS




LITERATURE CITED
















































TA

BL

E1

Dat

abas

eus

edin

the

com

para

tive

anal

ysis

ofth

ere

lati

onsh

ipbe

twee

nbo

dym

ass

and

song

freq

uenc

ies

For

acro

nym

sse

eM

etho

ds

Spe

cies

MA

X(H

z)M

IN(H

z)E

NF

(Hz)

BA

ND

(Hz)

Bod

ym

assa

(g)

Bea

kle

ngth

b

(mm

)P

hylo

gene

tic

posi

tion

c

Cur

ve-b

ille

dS

cyth

ebil

lC

ampy

lorh

amph

uspr

ocur

void

es2

610

147

02

417

114

033

058

0B

BB

BB

BB

BJB

CB

row

n-bi

lled

Scy

theb

ill

Cam

pylo

rham

phus

pusi

llus

305

01

100

226

51

950

396

500

BB

BB

BB

BB

JBB

Red

-bil

led

Scy

theb

ill

Cam

pylo

rham

phus

troc

hili

rost

ris

309

01

670

256

91

420

391

570

BB

BB

BB

BB

JBA

Lon

g-ta

iled

Woo

dcre

eper

Dec

onyc

hura

long

icau

da4

680

199

03

839

269

023

823

0B

BB

BB

AS

pot-

thro

ated

Woo

dcre

eper

Dec

onyc

hura

stic

tola

ema

407

02

160

382

61

910

181

200

BB

BB

AC

inna

mon

-thr

oate

dW

oodc

reep

erD

endr

exet

aste

sru

figul

a2

690

114

02

100

155

070

032

0B

BB

BB

BB

BJA

Taw

ny-w

inge

dW

oodc

reep

erD

endr

ocin

cla

anab

atin

a3

700

147

02

735

223

037

425

3B

BB

AB

BT

yran

nine

Woo

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eper

Den

droc

incl

aty

rann

ina

309

01

710

218

21

380

602

315

BB

BA

BA

Bar

red

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dcre

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Den

droc

olap

tes

cert

hia

278

01

340

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81

440

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BB

BB

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tes

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806

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062

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BB

BC

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fman

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hoff

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237

01

510

194

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213

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edge

-bil

led

Woo

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Gly

phor

hync

hus

spir

urus

521

02

520

406

03

690

146

120

BB

BB

BB

BA

Red

-bil

led

Woo

dcre

eper

Hyl

exet

aste

spe

rrot

ii2

560

140

02

030

116

011

40

370

BB

BB

BB

BB

LB

AA

Spo

t-cr

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epid

ocol

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saf

finis

883

02

400

600

86

430

354

150

BB

BB

BB

BB

KA

Lin

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dW

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epid

ocol

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sal

boli

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us3

910

228

03

666

163

033

328

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BK

BB

AN

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ocol

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338

01

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280

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BB

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esse

rW

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ocol

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399

01

420

305

22

570

218

215

BB

BB

BB

BB

H


TA

BL

E1

Con

tinu

ed

Spe

cies

MA

X(H

z)M

IN(H

z)E

NF

(Hz)

BA

ND

(Hz)

Bod

ym

assa

(g)

Bea

kle

ngth

b

(mm

)P

hylo

gene

tic

posi

tion

c

Whi

te-s

trip

edW

oodc

reep

erL

epid

ocol

apte

sle

ucog

aste

r6

390

224

04

750

415

036

0N

DB

BB

BB

BB

BK

BB

BA

Sca

led

Woo

dcre

eper

Lep

idoc

olap

tes

squa

mat

us3

460

232

03

356

114

027

026

7B

BB

BB

BB

BK

BA

Lon

g-bi

lled

Woo

dcre

eper

Nas

ica

long

iros

tris

183

01

340

171

349

092

076

0B

BA

Oli

vace

ous

Woo

dcre

eper

Sitt

asom

usgr

isei

capi

llus

497

01

670

350

83

300

143

170

BB

BB

BB

AW

hite

-thr

oate

dW

oodc

reep

erX

ipho

cola

ptes

albi

coll

is2

510

173

02

407

780

116

041

0B

BB

BB

BB

BL

BA

BB

BG

reat

Ruf

ous

Woo

dcre

eper

Xip

hoco

lapt

esm

ajor

350

01

100

241

72

400

155

058

0B

BB

BB

BB

BL

BA

BB

AS

tron

g-bi

lled

Woo

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eper

Xip

hoco

lapt

espr

omer

opir

hync

hus

522

02

000

305

23

220

136

052

0B

BB

BB

BB

BL

BA

BA

Ele

gant

Woo

dcre

eper

Xip

horh

ynch

usel

egan

s4

070

155

01

970

252

034

130

0B

BB

BB

BB

BB

Spo

tted

Woo

dcre

eper

Xip

horh

ynch

user

ythr

opyg

ius

293

01

710

258

31

220

468

ND

BB

BB

BB

BB

LA

Dus

ky-b

ille

dW

oodc

reep

erX

ipho

rhyn

chus

eyto

ni2

560

126

01

947

130

058

840

0B

BB

BB

BB

BC

Ivor

y-bi

lled

Woo

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eper

Xip

horh

ynch

usfla

viga

ster

330

01

630

258

31

670

472

ND

BB

BB

BB

BB

DB

uff-

thro

ated

Woo

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eper

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horh

ynch

usgu

ttat

us2

850

142

02

417

143

049

542

0B

BB

BB

BB

BG

Bla

ck-s

trip

edW

oodc

reep

erX

ipho

rhyn

chus

lach

rym

osus

232

01

260

164

31

060

564

397

BB

BB

BB

BB

IAB

Str

iped

Woo

dcre

eper

Xip

horh

ynch

usob

sole

tus

533

01

590

350

83

740

390

250

BB

BB

BB

BB

IAA

Oce

llat

edW

oodc

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erX

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chus

ocel

latu

s6

310

114

04

682

517

035

131

0B

BB

BB

BB

BIC

Che

stnu

t-ru

mpe

dW

oodc

reep

erX

ipho

rhyn

chus

pard

alot

us5

330

183

03

660

350

040

433

0B

BB

BB

BB

BF

Str

aigh

t-bi

lled

Woo

dcre

eper

Xip

horh

ynch

uspi

cus

252

085

02

251

167

041

629

0B

BB

BB

BB

BA

Spi

xrsquos

Woo

dcre

eper

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horh

ynch

ussp

ixii

431

01

380

203

02

930

312

325

BB

BB

BB

BB

IBO

live

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ked

Woo

dcre

eper

Xip

horh

ynch

ustr

iang

ular

is3

460

155

03

273

191

048

430

0B

BB

BB

BB

BE

aB

ased

onD

unni

ng19

93

bN

D

noda

ta

cA

fter

Rai

kow

(199

4)

and

acco

rdin

gto

the

conv

enti

onof

Pur

vis

and

Ram

baut

(199

5)

Thi

sco

nven

tion

cons

ists

inlo

okin

gat

each

node

ofth

eph

ylog

eny

and

lett

erof

its

daug

hter

bran

ches

W

hen

this

isdo

nefo

rea

chno

dein

turn

ea

chsp

ecie

sha

sa

uniq

ueco

defo

rmed

byth

ese

quen

ceof

lett

ers

onth

ebr

anch

esle

adin

gto

it

star

ting

from

the

root

(las

tco

mm

onan

cest

orof

all

the

spec

ies)



METHODS






RESULTS




Comparisons ba F P







Comparisons ba F P







DISCUSSION












ACKNOWLEDGMENTS




LITERATURE CITED
















































TA

BL

E1

Con

tinu

ed

Spe

cies

MA

X(H

z)M

IN(H

z)E

NF

(Hz)

BA

ND

(Hz)

Bod

ym

assa

(g)

Bea

kle

ngth

b

(mm

)P

hylo

gene

tic

posi

tion

c

Whi

te-s

trip

edW

oodc

reep

erL

epid

ocol

apte

sle

ucog

aste

r6

390

224

04

750

415

036

0N

DB

BB

BB

BB

BK

BB

BA

Sca

led

Woo

dcre

eper

Lep

idoc

olap

tes

squa

mat

us3

460

232

03

356

114

027

026

7B

BB

BB

BB

BK

BA

Lon

g-bi

lled

Woo

dcre

eper

Nas

ica

long

iros

tris

183

01

340

171

349

092

076

0B

BA

Oli

vace

ous

Woo

dcre

eper

Sitt

asom

usgr

isei

capi

llus

497

01

670

350

83

300

143

170

BB

BB

BB

AW

hite

-thr

oate

dW

oodc

reep

erX

ipho

cola

ptes

albi

coll

is2

510

173

02

407

780

116

041

0B

BB

BB

BB

BL

BA

BB

BG

reat

Ruf

ous

Woo

dcre

eper

Xip

hoco

lapt

esm

ajor

350

01

100

241

72

400

155

058

0B

BB

BB

BB

BL

BA

BB

AS

tron

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lled

Woo

dcre

eper

Xip

hoco

lapt

espr

omer

opir

hync

hus

522

02

000

305

23

220

136

052

0B

BB

BB

BB

BL

BA

BA

Ele

gant

Woo

dcre

eper

Xip

horh

ynch

usel

egan

s4

070

155

01

970

252

034

130

0B

BB

BB

BB

BB

Spo

tted

Woo

dcre

eper

Xip

horh

ynch

user

ythr

opyg

ius

293

01

710

258

31

220

468

ND

BB

BB

BB

BB

LA

Dus

ky-b

ille

dW

oodc

reep

erX

ipho

rhyn

chus

eyto

ni2

560

126

01

947

130

058

840

0B

BB

BB

BB

BC

Ivor

y-bi

lled

Woo

dcre

eper

Xip

horh

ynch

usfla

viga

ster

330

01

630

258

31

670

472

ND

BB

BB

BB

BB

DB

uff-

thro

ated

Woo

dcre

eper

Xip

horh

ynch

usgu

ttat

us2

850

142

02

417

143

049

542

0B

BB

BB

BB

BG

Bla

ck-s

trip

edW

oodc

reep

erX

ipho

rhyn

chus

lach

rym

osus

232

01

260

164

31

060

564

397

BB

BB

BB

BB

IAB

Str

iped

Woo

dcre

eper

Xip

horh

ynch

usob

sole

tus

533

01

590

350

83

740

390

250

BB

BB

BB

BB

IAA

Oce

llat

edW

oodc

reep

erX

ipho

rhyn

chus

ocel

latu

s6

310

114

04

682

517

035

131

0B

BB

BB

BB

BIC

Che

stnu

t-ru

mpe

dW

oodc

reep

erX

ipho

rhyn

chus

pard

alot

us5

330

183

03

660

350

040

433

0B

BB

BB

BB

BF

Str

aigh

t-bi

lled

Woo

dcre

eper

Xip

horh

ynch

uspi

cus

252

085

02

251

167

041

629

0B

BB

BB

BB

BA

Spi

xrsquos

Woo

dcre

eper

Xip

horh

ynch

ussp

ixii

431

01

380

203

02

930

312

325

BB

BB

BB

BB

IBO

live

-bac

ked

Woo

dcre

eper

Xip

horh

ynch

ustr

iang

ular

is3

460

155

03

273

191

048

430

0B

BB

BB

BB

BE

aB

ased

onD

unni

ng19

93

bN

D

noda

ta

cA

fter

Rai

kow

(199

4)

and

acco

rdin

gto

the

conv

enti

onof

Pur

vis

and

Ram

baut

(199

5)

Thi

sco

nven

tion

cons

ists

inlo

okin

gat

each

node

ofth

eph

ylog

eny

and

lett

erof

its

daug

hter

bran

ches

W

hen

this

isdo

nefo

rea

chno

dein

turn

ea

chsp

ecie

sha

sa

uniq

ueco

defo

rmed

byth

ese

quen

ceof

lett

ers

onth

ebr

anch

esle

adin

gto

it

star

ting

from

the

root

(las

tco

mm

onan

cest

orof

all

the

spec

ies)



METHODS






RESULTS




Comparisons ba F P







Comparisons ba F P







DISCUSSION












ACKNOWLEDGMENTS




LITERATURE CITED

















































METHODS






RESULTS




Comparisons ba F P







Comparisons ba F P







DISCUSSION












ACKNOWLEDGMENTS




LITERATURE CITED

















































Comparisons ba F P







Comparisons ba F P







DISCUSSION












ACKNOWLEDGMENTS




LITERATURE CITED























































ACKNOWLEDGMENTS




LITERATURE CITED

















































LITERATURE CITED


























































Documents

DOES BEAK SIZE AFFECT ACOUSTIC FREQUENCIES IN WOODCREEPERS?