Vol.1938 55]J BRAND,Vibration Frequencies ofPassefine Song 263

VIBRATION FREQUENCIES OF SONG•

BY ALBERT R. BRAND

T•E recordingof bird songson film producesa medium from which soundscan be studiedobjectively; hence we needno longerrely entirely on aural impressions.There, on the film, is printedin black and white, on a soundtrack of varyingdensity or varyingarea, dependingon whichof two methodsof recordinghas been used, the picturethat the physicalvibrations have madeupon the sensitizedfilm. The numberof thesevibrations per seconddetermines the pitch of a sound. •Forexample: a soundof 4096 vibrationsper secondis pitchedat the highestnote of the pianokeyboard (C?) and is said to have a frequencyof 4096. Bird songsmay alsobe re- cordeddirectly on wax, from whencephonograph records can be manu- factured. This method,while satisfactoryfor purposesof reproduction,is not so accurateas film for objectivestudy. In 1934 in Germany,and in 1935-37 in England, Ludwig Koch recordedbird songsdirectly on wax. He reportson the pitchof someten passerincbird songs(Nicholson, E. M., andKoch, Ludwig, 'Songs of Wild ,'London, p. xxviii, 1936).The data are, however,fragmentary; he givesonly the highestand lowestfrequencies found. Thosehe reportson are lower,so far as the highestnotes are con- cerned,than the resultsof my studieswould indicatefor Americanbirds. The highestfrequency he mentionsis 5500 for the Yellow-hammer(ibid., p. 3). But one gathersfrom what he writes that it is unlikely that he is getting all the highspresent in bird song;probably somewhere in his ap- paratushe losesor partially suppressesthem. Thereare a numberof places wherethis lossis likely to occur. Unlessmicrophone, amplifiers and re- corderare very carefullycoordinated and speciallyconstructed, this is in- evitable; in addition, it is doubtful whetherit is practicalto constructa disk recordersuch as Koch uses,that will reproducemuch over 5000 vibra- tions per second. In other words,songs containing frequencies over 5000 vibrationswould probablybe reproducedonly in part in disk recording. On film, however,we have recordedin Nature, bird and insectsounds of a frequencyof over 10,000vibrations, and we havemade laboratory tests up to 17,000. It is thereforeunsafe to includethese European recordings in our calculations,at leastuntil numericallyfar more studieshave beenmade than are yet reported,and until we have definiteproof that theserecordings includethe higherfrequencies. In almostevery casemy studieswere madefrom originalnegative film, producedby either the variable-densityor the variable-area recording

• Read at the Fifty-fifth Stated Meeting of the American Ornithologists' Union, Charleston, November 17, 1937. 264 BR•N.,Vibration Frequencies ofPassefine Song [April[Auk method. Perhapshalf a dozen studieswere made from positive prints. Variable-area and variable-densityfilms give essentiallysimilar results, with the main differencethat varying-area track producesmore visual detail than oneof varyingdensity. As at presentwe are concernedwith the pitch-giving frequencyof the songsof birds, either type of recordingis satisfactoryfor study. Were we discussingthe important factor of bird song,quality, or what musicianscall timbre, we shouldfind variable-area film more valuable for study. But thus far, in most of the studies,I have not attempted to analyze the sound further than to discoverthe main or pitch-giving frequency; and these remarks are restricted to pitch. The study of quality is highly involved,requiring in most easesa study of com- plicated wave shapes in order to determine the overtones or harmonies. This necessitatesintricate mathematical calculations. It is agreed that quality--that whichenables us to recognizea Meadowlark'snote immedi- ately, and not to confuseit with, let us say, a warbler'snote given on the samepitch--is of fundamentalimportance. At somefuture time I hopeto have sufficientmaterial to offer the resultsof investigationson that phase. For the present,let us restrict our considerationsto the main pitch-giving frequency. In the past few years, in the Laboratory of Ornithologyat Cornell Uni- versity, we have studied intensivelyunder a low power of magnification (25 diameters),several hundred pieces of film comprisingthe songsand calls of about one hundredspecies of birds. In orderto simplifymatters, I am in this paper, consideringsongs only. That is, I have taken what is generallyaccepted as song,and giventhe results;and in order to simplify further, I shall consideronly passefinesong. Thus I have reducedthe results so that we have studiesof fifty-nine passefinebird songs. The familiesand the numberof speciesincluded are as follows:Tyrannidae, six; Corvidae,one; Paridae, one; Troglodytidae, three; Mimidae, one; Turdidae, six; Bombyeillidae,one; Sturnidae,one; Vireonidae,three; Compsothlypi- dae, sixteen;Ieteridae, six; Thraupidae, one; Fringillldae, thirteen. These specieswere selected at randomand give a fair generalsample of passerine song. Almost no bird notesremain on the samepitch from instant to instant. That is, birds almostinvariably slur either upwardor downward,and often in both directions. I have attempted to estimatethe bird songson what appearsto be the approximatemean of all frequenciesin a note, and also the mean of the song. Though a note may contain a very short portion (sometimes0.002 secondsin duration) of either excessivelyhigh or rather low frequency,I have attemptedto approximatethe main pitch of the note, which in many eases,is the pitch of longestduration and sometimesthe pitch which is Vol.1938 55]J BRAND,Vibration Frequencies ofPasserinc Song 265 loudest. In many notesthe pitch is changingconstantly, and in thesecases I have, as nearly as possible,estimated the average. While it is possibleto count accuratelythe frequencies,these estimatesare merely approxima- tions. However, they are correctwithin, let us say, two or three per cent. Thus a note which I have called a frequencyof 5000 vibrationsmight be 4850 or 5150, but the error will rarely be greater than that, and in most easesis considerablyless. Thesedifferences are so slight as to be negligible, being lessthan one-quarterof a note. Errors may occur,in the following ways. In making a recording,the motor that drives the film through the recordermay occasionallybe slightly slow or fast. However, this is very carefullywatched, and it rarely happensthat the film speedis not accurate; and when it is not, the differenceis so slight as to be negligible. In esti- matingfrequencies by inspeetlonno attempt is made at absoluteaccuracy. Here again the introducederror is very slight. This has been proved a number of times by estimatingindependently, on separatedays, the re- sults of the studiesof successivesongs of the same bird. The results of these cheeksare always the same. The introducederror of estimationis very small; often two separatelymade countsgive absolutelyidentical results. We thus have assurance that the method used is accurate for all practical purposes. Of the fifty-nine songsincluded in this study we find, by the method described,that the averagepitch of passerincbirds' songis 4280 vibrations, or a quarter note higher than C7, the highestnote of the piano keyboard. This is about an octaveand a half higher than the highestnote that an operatleeoloratura soprano can reach. The averageof 4280 for fifty-nine speciesgives, I believe, a fairly correct estimationof all passerincsong. However, there is great variation within the group. The averageof Wood Warbler songsis considerablyhigher: for the sixteenspecies included in thesestudies, it was found to be 5350, or a shadehigher than the E above the highestnote on the piano keyboard. This is two noteshigher than the averageof passerincsong. In the thrush group, of which the songsof six specieswere studied, the averagewas about 2890, which is a shadeunder the highestF sharpon the piano,or F sharp6, approximatelythree notes lower than the average. Ieterine songalso is comparativelylow, and we foundin the six speciesstudied, exactly the same, i.e., 2890, as in the Turdidae. Fringillinebird songon the wholeis high, althoughit includesthe Cardinal whoseclear, whistling tune averageslower than one would presume. The Cardinal songis 2800, or a shadeabove the highestF (F6) of the keyboard. The songsof thirteenfringilline species studied, showed an averageof 4800 or just underD sharp7, the D sharpabove the highestnote (C?)of the key- board. The highestsong studied was the Black-pollWarbler's. Its averagenote 266 BRANV,Vibration Frequencies ofPasserins Song œArril]'Auk was8900 or overan octaveabove the highestnote on the piano. It is mid- way betweenC sharps and Ds. The Blackpoll also producedthe highest avian frequencystudied, 10,225, a note about a quarter under Es. Other high averageswere countedfor birds in the followingorder: Grasshopper Sparrow,8600; CedarWaxwing, 8400; Blue-wingedWarbler, 7675; Black- burnJanWarbler, 7300; Black and White Warbler, 6900. The differencein frequencybetween the first three, Blackpoll, GrasshopperSparrow and CedarWaxwing, is only about a half a note, and is so smalland the pitch so high, that an ear would have to be remarkably accurateto recognizethe pitch difference.

COUNT OF PITClt OF PASSERn•IE BIRD SONGS For further referencefor thoseinterested in the subject,the following table givesfigures for all songsreported on in this paper. The birds are listed under their common names as given in the fourth edition of the A. O. U. 'Check-list,'grouped by familiesin systematicorder.

A pproxi- Highest Lowest No. of songs mate note note studied mean (about) (about) TYRAN'NIDAE Eastern Kingbird ...... 1 6225 6225 5850 Eastern Phoebe ...... 2 4300 5200 3300 Alder Flycatcher ...... 3 3300 4750 1925 Little Flycatcher ...... 1 3500 5125 2375 Eastern Wood Pewee ...... 1 4125 4375 3650 Olive-sidedFlycatcher ...... 1 3100 3850 2375 CORVIDAE Eastern Crow ...... 1 1500(?) 1650 1450 PARIDAE Black-cappedChickadee ...... I 3300 3700 3025 TROGLODYTIDAE Eastern House Wren ...... 1 4100 7125 2050 Eastern Winter Wren ...... 1 5000 8775 3300 Long-billedMarsh Wren ...... 1 4400 5475 1925 MIMIDAE Catbird ...... 1 3000 4375 1100 TURDIDAE Eastern Robin ...... 1 2800 3300 2200 Wood Thrush ...... 1 2750 4025 1825 Eastern Hermit Thrush ...... 1 3000 4375 1475 Olive-backed Thrush ...... 1 2925 3850 2000 Veery ...... i 3300 4750 2375 Eastern Bluebird ...... 1 2550 3100 2200 BOMBYCILLIDAE ...... 1 8400 8950 7675 ¾ol.1938 55]J BRAND,Vibration Frequencies ofPasserine Song 267

A pproxi- Highest Lowest No. of songs mate note note studied mean (about) (about) STURNIDA•E Starling...... 1 3475 8225 11oo VIREONIDAE White-eyed Vireo ...... 1 2800 3825 1925 Yellow-throated Vireo ...... 1 2750 3825 2325 Red-eyed Vireo ...... I 3600 5850 2375 COMPSOTHLYPIDAE Black and White Warbler ...... 1 6900 8050 5300 Blue-wingedWarbler ...... 1 7675 8050 7125 Tennessee Warbler ...... 1 6600 9150 4025 Eastern Yellow Warbler ...... 1 5900 8775 3475 Black-throated Green Warbler ...... 2 6025 6750 5125 BlackburnJan Warbler ...... 1 7300 8775 5475 Chestnut-sided Warbler ...... 1 5125 8775 3100 Black-poll Warbler...... 4 8900 10225 8050 Northern Warbler ...... 1 4150 5125 3300 Oven-bird ...... 2 4000 5850 3300 Northern Water-Thrush...' ...... 1 2925 3850 2000 Louisiana Water-Thrush ...... 1 4000 6600 2475 Mourning Warbler ...... I 3300 5125 2375 Yellow-breasted Chat ...... I 2600 4400 1275 Hooded Warbler ...... 1 4000 5850 2925 American Redstart ...... 1 6200 7300 4400 ICTERmAE Bobolink ...... 1 3000 6950 ? Eastern Meadowlark ...... 1 4400 6025 3150 Western Meadowlark ...... 1 2500 3475 1475 Yellow-headed Blackbird ...... 3 2000 ? ? Eastern Red-wing...... 1 2925 4375 1450 Baltimore Oriole ...... 1 2500 3825 2O5O THRAUPIDAE ScarletTanager ...... 1 2925 5625 2200 FRINGILLIDAE Eastern Cardinal ...... 1 2800 4375 2200 Indigo Bunting ...... 1 5700 8875 3250 Eastern Goldfinch ...... 1 4100 7400 2750 EasternSavannah Sparrow ...... 1 5000 8775 3300 EasternGrasshopper Sparrow ...... 2 8600 9500 7675 Eastern Henslow'sSparrow ...... 3 4200 6200 3425 EasternVesper Sparrow ...... 2 4800 6600 2750 Slate-colored Junco ...... 1 4750 5500 3850 Eastern Chipping Sparrow...... 3 5000 8400 3475 Western Chipping Sparrow...... 1 4000 5500 3300 Eastern Field Sparrow...... 1 4100 5100 3650 SwampSparrow ...... 2 5250 7500 2925 EasternSong Sparrow ...... 4 4700 7700 1900 268 BRAND,Vibration Frequencies ofPasserinc Song [April[Auk

To summarize:I believethat thesestudies are sufficientlycomprehen- sive to warrant the conclusionthat passerincsong averagesabove 4000 vibrationsper secondor aroundthe highestnote of the pianokeyboard. Laboratoryof Ornithology CornellUniversity, Ithaca, New York