ONTOGENY OF VOCALIZATION IN THE GREATER RHEA PAUL W. BEAVER Department of Psychology,University of Washington,Seattle, Washington98195 USA ABST•CT.--The call-notesof the Greater Rhea chick were classifiedaccording to their acous- tical structureand behavioralcontext. Both rate of vocalizationand tonal quality of call-noteswere found to deteriorateas a function of maturation. Call-note productionwas completelyeliminated by 7 weeksof age. Greater Rhea adultsare silentexcept for suchrelatively infrequent vocalizations as "hissing"that sometimesaccompanies agonistic behavior and a disyllabic"grunt" that only the male producesas part of a courtship display. Tracheal growth and a marked reduction in the intrusion of the internal tympanic membranes into the bronchial passagescould contribute to the deteriorationof vocalization.The use of vocalizationas the primary channel of communicationis replaced by visual display in the adults. These modalities are best suited to the ecologicalcon- tingencies facing the chick and adult, respectively. Received 17 March 1977, accepted24 Sep- tember 1977. A greatdeal of ornithologicalliterature has focusedon the vocal displaysof birds (e.g. Thorpe 1961, Hinde 1969, Armstrong 1973). The attention accordedto bird vocalization is no doubt largely due to its central importance in avian social interac- tion. The suborderoscines of the passerinebirds have been the most popular species for research in bird vocalization. There has been little interest in the vocalizations of nonoscinesin general and ratite birds in particular. This is probably becausethe vocal repertoire of adult ratites is not very impressive. The Greater Rhea (Rhea americana), a large, flightlessratite native to the pampasof Argentina, is especially unimpressive.In the adult, vocal productionis restrictedto "hissing"during agonis- tic encountersand the disyllabic "grunt" of a sexually arousedmale. In contrast to adults, Greater Rhea chicks are highly vocal. This is unlike most other speciesof birds whosevocal repertoiresincrease in complexityas a function of development. The ontogenyof vocalizationin the Greater Rhea is a curiousexample of behavioral regressionand may posequestions for theoretical treatments of behavioral ontogeny that treat it as a cumulative and progressiveprocess. METHODS Eggs were laid by the Greater Rheas maintained at the Chicago Zoological Park, Brookfield, Illinois and incubated at the University of Chicago. A total of 33 chicks was hatched over 2 years, of which 20 survived past 2 months of age. Chicks were housedat the University of Chicago in a 0.9 x 1.2 m pen until 4 weeksof age, at which time they were transferredto a 90 m2 outdoorenclosure at the ChicagoZoological Park. Vocal behavior was recorded on a SONY tape recorder model TC-92. Over 20 h of vocalizationswere recorded and are available upon request to the author. Sonagramswere made on a Kay Elemetrics, Co. audio spectrumanalyzer model 6061 B. Vocal amplitude was determinedby a linear scalesound level meter placed at a distanceof approximately 1 m from the chick. Recordingswere made daily at random times for the first 4 weeks of life. Additional recordingswere also made on an intermittent basisbetween ages 4-8 weeks. CALL-NOTE CATALOGUE Several authors, from Hudson (1903) to Bruning (1973a), have used the phrase "plaintive cry" to describea frequentlyheard ca]] of the Greater Rhea chick. Bruning 382 The Auk 95: 382-388. April 1978 April 1978] RheaVocalization Ontogeny 383 kliz kliz B 8 8 2- ; 0.5 1'.0 œ5 i.o kllz c kHz O 2 ) •5 0.5 1.0 15 kllz E 8- 6- 4- 2- 0.5 1.0 ]'.5 l'.O Sec. Sec. Fig. 1. Type B/65 wide-bandsonagrams of GreaterRhea chick call-notes: (a) contact-whistle,(b) separation-whistle,(c) alarm-trill,(d) feeding-peep,(e) contentment-chirp,(f) separation-whistleof an older chick illustrating tonal deterioration. also makesreference to an infrequentlyheard alarm cry producedwhen the chick was in immediatedanger. Beyond these observations no one has madea detailed catalogueof GreaterRhea chick call-notes. Basedon observationsof captivechicks in a variety of experimentalconditions, five call-notes(Fig. 1) weredetected and investigated. The call-noteswere supplied with terms that reflect both their function and sound: (1) contact-whistle; (2) separation-whistle;(3) alarm-trill;(4) feeding-peep;and (5) contentment-chirp. Contact-whistle.-•The contact-whistle call-note sounds much like a soft, short whistle.It is a brief, monosyllabiccall-note, with a durationof 0.20-0.50 s. It is also of relativelylow amplitude,rarely exceeding 75 db. The fundamentalfrequency is generallyaround 1.5-2.0 kHz. There are severalharmonics, at about2.0 kHz inter- vals, whichreflect the brillianceof the tone.Some chicks have a sharpdecrease in pitchat the endof the note,while othersexhibit a sharpdecrease at the beginningof the note;with othersthere are no suddenchanges in pitch. Thesevariations appear to be specific to individuals. The contact-whistlecall-note was initially heard after the GreaterRhea embryo 384 PAUL W. BEAVER [Auk, Vol. 95 enteredthe air space(determined by candling),generally 2-5 days prior to hatching. The contact-whistlewas emitted spontaneouslyby the embryo. It was alsoelicited on several occasionsin responseto the tape recorded playback of this call as well as to such mild stimulation as the slow turning of the egg. Such in-egg vocal production may act to synchronizethe hatchingof GreaterRhea eggsthat are incubatedtogether in a clutch. Pilot researchby Bruning (1973b) indicated spectacularhatching syn- chrony, acceleratingthe time to hatchingof late set eggsby as much as 7 days. In-egg vocal behavior in other speciesmay be a potential variable in hatching synchrony (Orcutt 1974). The contact-whistleremains very prominent in the repertoireof the Greater Rhea chick after hatching. It was frequently emitted in the presenceof a human surrogate parent, especiallywhen the chick was following or approaching.It was also fre- quently emitted in the presenceof conspecificswith which the chick was reared. Since the call-noteis heard only in thesesituations I suggestthat it servesa social contact function. Separation-whistle.--The separation-whistlecall-note soundsmuch like a loud, long whistle. This call-note is the "plaintive cry" documentedby Hudson (1903) and Bruning (1973a). It is a long, monosyllabiccall-note, generallylasting 1.0-3.0s. The longest separation-whistlerecorded was 4.48 s. The separation-whistleis a high amplitude call-note, reaching 75-100 db. The fundamental frequency is generally around 2.0 kHz. There are several harmonics, at about 2.0 kHz intervals, which reflect the brilliant tonal quality of the call-note. There are severalindividual-specific variations in pitch changesduring separation-whistles.Some variations involve a sudden or gradual frequency decrease,which intensifiesthe sad or lonely quality of the call-note to the human ear. The fundamental remains level for some chicks while for othersit gradually decreases,by 0.1-1.0 kHz, over 1-3 s. Some chicksshow a sudden decreasein frequency at the onset of the call-note, while others show a sudden increase, but most chicks have neither. Some chicks show a sudden decrease in frequency at the tail of the call-note while others do not. The separation-whistleis first heard within a few hours after hatching. The separation-whistleappears to be functionally related to the contact-whistle.Whereas the contact-whistleis emitted when the surrogateparent or familiar conspecificsare nearby, the separation-whistle is emitted in a condition of social isolation or when with unfamiliar conspecifics.The separation-whistlealso appearsto be acoustically related to the contact-whistle;its distinctionis that it is longerand louder. There is no clear border between the two call-notes.If the surrogateparent is gradually displaced to some distance but the chick retains visual contact, the contact-whistle escalatesin both duration and amplitude, gradually assumingthe character of a separation- whistle. The inter-individual variations in pitch at the termination of the contact- whistle reflect thoseof the separation-whistle,again suggestinga closerelationship between the two call-notes. Alarm-trill.--The alarm-trill call-note has many acoustical features in common with the separation-whistle.It is a long, loud monosyllabiccall-note. The durationis generally somewhat shorter than that of the separation-whistle,lasting 0.5-2.0 s. The amplitude measures80-90 db. The fundamental frequencyis generallyaround 2.0 kHz. There are severalharmonics, at about2.0 kHz intervals.The distinguishing feature of the alarm-trill is a modulationof pitch throughoutthe call-note. The alarm-trill is elicited by stressingthe chick with suchprocedures as suddenly lifting it off the ground or by administeringintra-muscular injections of medicine or April 1978] RheaVocalization Ontogeny 385 vitamin supplement.The alarm-trill is not heard from all chicksas someconsistently remain silent throughout these procedures. The alarm-trill is acousticallysimilar and seemsto be functionally related to the separation-whistle.Both probably function to attract the parent to the chick. But the modulationof pitch in the alarm-trill may serveto give it somewhatgreater emphasis or urgency than the separation-whistle. Feeding-peep.---Thefeeding-peep is a very quiet, short, monosyllabiccall-note. From one to four feeding-peepsare generallyemitted in rapid succession.The dura- tion of a singlefeeding-peep is usually0.15-0.20 s. The amplitude was not