Aggressive Response of Red-Winged Blackbirds to Mockingbird Song

584 ShortCommunications [Auk, Vol. 99

AggressiveResponse of Red-wingedBlackbirds to MockingbirdSong Imitation

ELIOT A. BRENOWITZ Sectionof Neurobiologyand Behavior,Seeley G. Mudd Building,Cornell University, Ithaca, New York 14853 USA Vocalmimicry by birds haslong received attention wing copywas used.The Red-wing songused in the but is still not well understood.Several hypotheses playbackswas recorded from a territorial blackbird have been advancedto explain its adaptive signifi- nearIthaca using a SennheiserMKH 815Tcondenser cance (Harcus 1977, Rechten 1978, Dobkin 1979, microphoneand a Nagra IV-D recorder. Krebs and Kroodsma 1980). Proposed functions of As can be seen from Fig. 1, the mimic song is of mimicry include: (1) interspecificterritorial defense, excellentquality. Like the true Red-wingsong, it con- (2) increasedsize of songrepertoire for mate attrac- sistsof a sequenceof introductorynotes followed by tion and/or intraspecificterritoriality, (3) facilitation a pulsedtrill. Both songscontain major energyfrom of individual recognition, and (4) increasesin the about 2.8 to 3.7 kHz. The temporal structure of the apparent density of resident predators and/or com- trills in both songsis quite similar. I have shown petitorsthrough deception.Both Dobkin (1979)and previously that the trill is both necessaryand suffi- Rechten(1978) have suggested that, if the copiedsig~ cientfor speciesrecognition in Red-wings(Brenowitz nal is to be used by the mimic in intraspecificinter- 1980, 1982). actions, then extremelyaccurate mimicry shouldnot The playback procedure used in the present ex- be selected for, as it would decrease the chance of periment was the same as described in detail in the songbeing perceivedas belongingto the mimic. Brenowitz(1981). Briefly, Red-wingswere exposed One measureof the fidelity of the mimickedsignal to playbackof Mockingbird imitation both before is whether individuals of the model speciesrespond and after playback of conspecificsong, either in differentially to the presentation of imitation song early morning (0500-0800)or early evening (1900- and of true conspecificsong. 2100).Each signal was presentedat 15-s intervalsfor Morton (1976) observedthat, when he approached 3 min, followed by 1 min of post-playbackobser- the nests of Thick-billed Euphonias(Euphonia lani- vation. The birds' responsesto these signalswere irostris), they gave the alarm calls of other bird quantifiedby five criteria:(1) the number of songs speciesnesting nearby and that these calls evoked given during the 4-min playback period, (2) the mobbingby individualsof the model specieswhile number of songspreads given during the 4 min pe- the euphonia remained still and continued mimick- riod, (3) the number of songspreads judged to be of ing. Lemaire (1975) found that Willow Warblers high intensity, (4) the percentageof songsduring the (Phylloscopustrochilus) and Chaffinches (Fringilla playbackperiod that were accompaniedby a song coeIebs)did not distinguishbetween playbackof spread, and (5) the percentageof song spreads conspecificvocalizations and of isolated imitations judged to be of high intensity. The song spread is by Marsh Warblers (Acrocephaluspalustris). a gradedvisual displaythat often accompaniessong Mockingbirds (Mimus polyglottos)produce excel- and that reflectsa correspondinggradation of ag- lent imitations of severalbird species(Bent 1948). It gressivearousal (Orians and Christman 1968, Peek is unknown, however, whether individuals of the 1972, Yasukawa 1981). Data were tested with a Fried- mimicked speciescan distinguishthese copiesfrom man two-way analysisof varianceby ranks (Siegel true conspecificsignals. Using a previously estab- 1956). lished playbacksystem with Red-wingedBlackbirds Table 1 presentssummary data for 10 Red-wings. (Agelaius phoeniceus)(Brenowitz 1981), I tested For all five responsemeasures, there was no signif- whether Mockingbird imitation of Red-wing song icant differencein strengthof responseto playback was of sufficientquality to deceiveblackbirds. of true Red-wing songand of a Mockingbird imita- From 2-5 July 1981 I conducteda seriesof experi- tion. Most of the blackbirds tested showed robust, ments near Ithaca, New York in which I compared strongly aggressiveresponses immediately upon the strength of responseof 10 territorial Red-wings presentationof the mimic song. to playback of conspecificsong and to playback Theseresults strongly suggest that Red-wingsare of a Mockingbird imitation. These songsare shown unableto distinguishbetween conspecific song and in Fig. 1. The mimic songwas recordedby J. C. Glase isolatedMockingbird imitation. Mockingbirds could, in Reading,Pennsylvania on 19 June 1966at a dis- therefore,potentially use their imitationof Red-wing tance of about 15 m and is archived in the Cornell songin interspecificterritoriality directed at black- Library of Natural Sounds(catalog number 11117). birds. The fact that naturally occurringmimics learn The Mockingbird delivered three successiverendi- Red-wing song indicatesthat these two speciesare tions of Red-wing songin a sequenceof about 5 min sometimes sympatric. Support for this function of of continuoussong that included imitations of sev- Mockingbird song mimicry comesfrom the obser- eralother species.In the playbacks,one isolatedRed- vationsthat they are generalistfeeders that are high- 585 1982] Short Communications

IIIIIIIII

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i i i 2 4 6 8 0.4 0.8 I. 2 Frequency (kHz) Time (sec)

IIIIIIIII (B)

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Fig.1. Red-wingedBlackbird song (A) and Mockingbird imitation ofRed-wing song (B) used in playbacks.Wide-band sound spectrograms in left column, power spectra in rightcolumn. ly aggressivetoward a largenumber of species presentstudy does not, of course,prove that Mock- (Moore1978) and that they imitate the songs of many ingbirdmimicry functions in interspecificterritori- of theircompetitors (J. Bay[is pers. comm. to Krebs ality.Additional research is neededto resolvethis andKroodsma 1980). One additionalpoint thatis of question. related interest is that, while making the original The resultspresented in this reportdemonstrate Mockingbirdrecordings, Glase noted that whena thatMockingbirds are able to produceimitations of CommonFlicker (Colaptesauratus) landed nearby extraordinaryfidelity. Further experiments might be andcalled, the Mockingbirdresponded by mimick- conductedto examinethe responseof Red-wingsto ingit. Thisalso happened when an American Robin mimickedblackbird song presented in thecontext of (Turdusmigratorius) approached and "scolded." The completeMockingbird song. Also, it wouldbe in-

TABLE1. Responses (f --+SD) shown by Red-winged Blackbirds toplaybacks ofMockingbird imitation of Red-wingsong both before and after playback oftrue Red-wing song. x2r values computed with Friedman two-wayanalysis of variance; n = 10for all tests; * indicates P • 0.05. Mockingbird Mockingbird imitation Red-wingsong imitation Numberof songs 16.1_+ 7.0 13.2+ 7.5 13.7_+ 6.2 x•r = 4.85* Numberof song spreads 15.1-+ 8.4 12.6_+ 8.2 12.9+ 7.1 x•r = 3.15' Numberof high-intensity 13.3-+ 9.4 11.9_+ 8.9 10.9_+ 7.6 songspreads x2r= 2.16' Percentagehigh-intensity 60.4-+ 43.5 81.8-+ 32.8 72.6_+ 34.2 songspreads x2r= 1.05' Percentagesongs accompanied 74.9_+ 37.7 88.6_+ 21.3 85.1+ 31.6 bysong spread x•r= 0.35* 586 ShortCommunications [Auk, Vol. 99 teresting to know whether other mimicked species KREBS,J. R., & D. E. KROODSMA.1980. Repertoires are similarly unable to distinguishthe copied from and geographicalvariation in bird song. Pp. the model vocalization. 143-177 in Advances in the study of behavior, My thanks to R. Chariff for bringing the Mocking- vol. 11. (J. S. Rosenblatt, R. A. Hinde, C. Beer, bird imitation of Red-wing songto my attentionand and M.-C. Busnel, Eds.). New York, Academic to J. Gulledgefor providingaccess to recordingsin Press. the Cornell Library of Natural Sounds. D. Koutnik LEMAIRE, F. 1975. Le chant de la Rousserolle ver- and D. D0bkin made helpful comments on the derolle (Acrocephaluspalustris): fid•lit• des imi- manuscript.R. Capranicaallowed me to use facilities tations et relations avec les esp•ces imit•es et supportedby NIH grant NS 09244. This work was avec les cong•n•res. Gerfaut 65: 3-28. partially supportedby a grant-in-aid from the na- MOORE,1•. R. 1978. Interspecificaggression: toward tional division of SigmaXi. whom shoulda Mockingbirdbe aggressive?Be- hav. Ecol. Sociobiol. 3: 173-176. LITERATURE CITED MORTON,E. S. 1976. Vocal mimicry in the Thick- billed Euphonia. Wilson Bull. 88: 485-487. BENT, A. C. 1948. Life histories of North American ORIANS, G. H., • G. M. CHRISTMAN. 1968. A com- nuthatches, wrens, thrashers and their allies. U.S. Natl. Mus. Bull. 195. parative study of the behavior of Red-winged, Tricolored, and Yellow-headed blackbirds. Univ. BRENOWITZ,E. A. 1980. Long-range communication California Publ. Zool. 84: 145. of species identity in the song of the Red- PEE•C,F. W. 1972. An experimentalstudy of the ter- winged Blackbird. Amer. Zool. 20: 789. (Ab- ritorial function of vocal and visual display in stract). the male Red-wingedBlackbird (Agelaius phoe- 1981. The effect of stimulus presentation niceus). Anim. Behav. 20: 112-118. sequenceon the responseof Red-wingedBlack- R•CHT•N, C. 1978. Interspecificmimicry in bird- birds in playbackstudies. Auk 98: 355-360. song: does the Beau Geste hypothesis apply? --. 1982. Long-rangecommunication of species Anim. Behav. 26: 305. identity by song in the Red-winged Blackbird. Behav. Ecol. Sociobiol. 10: 29-38. S•EG•L, S. 1956. Nonparametric statistics. New York, McGraw-Hill Book Co. DOB•C•N,D. S. 1979. Functionaland evolutionaryre- YASUKAWA,K. 1981. Song repertoires in the Red- lationships of vocal copying phenomena in birds. Z. Tierpsychol.50: 348-363. winged Blackbird(Agelaius phoeniceus): a test of the Beau Geste hypothesis. Anim. Behav. 29: •IARcUS,J. L. 1977. The functionsof mimicry in the 114-125. vocal behaviour of the Chorister Robin. Z. Tier- psychol. 44: 178-193.

ReproductiveSynchrony and PredatorSatiation: an AnalogyBetween the Darling Effectin Birds and Mast Fruiting in Plants

MICHAEL GOCHFECD Departmentof Environmentaland Community Medicine, College of Medicineand Dentistry of New Jersey, RutgersMedical School, Piscataway, New Jersey08854 USA Breeding synchrony characterizes many taxa. allowing some to survive as predatorsbecame sa- Some factorsimpose or selectfor synchrony,while tiated. Darling's model is attractivein linking evo- others entrain it on a more immediate, proximate lution and ecology(selection via reducedpredation) basis. Observed synchronyin a population repre- with behavior and physiology(social facilitation in sentsa compromisebetween synchronizingand de- large groups enhancingneuroendocrine stimulation synchronizingfactors. Avian ecologiststrace discus- leadingto increasedsynchrony). Despite this attrac- sion of synchronyto F. FraserDarling (1938), who tiveness, few studies have found support for the proposedthat, in gulls, synchronywas adaptive in model. A relationbetween synchrony and groupsize minimizing predation on young. He assumedthat or improved productivity is demonstrablein some a predator has a finite appetite and that there is no studies (Hall 1970, Collias et al. 1971, Burger 1979, recruitment of predators (Gochfeld 1980: 256). As Gochfeld 1979), while Nisbet (1975) found evidence long as the numberor biomassof youngwas below for timing and predatorsatiation. Some studies have this predation threshold(a term he did not use), all found no evidence for the model (Orians 1961, might be consumed.Synchronous hatching would MacRoberts & MacRoberts 1972). yield a superabundanceof young for a brief period, The complexities of studying these interrelated