The Auk 111(2):300-313, 1994 VOCAL LEARNING IN GREY PARROTS (PSITTACUS ERITHACUS): EFFECTS OF SOCIAL INTERACTION, REFERENCE, AND CONTEXT IRENE M. PEPPERBERG Departmentof Ecologyand EvolutionaryBiology, University of Arizona, Tucson,Arizona 85721, USA ABSTR•cr.--Formany passerines,the extent,timing, and even presenceof allospecificvocal learning can be influencedby the form of input that is received.Little data exist,however, on vocal learning in parrots (Psittacidae). I have previously proposed that such vocallearning proceeds most readily when input is (1) referential,(2) contextuallyapplicable, and (3) interactive.The referentialaspect demonstrates the meaningof the codeto be taught, the contextualaspect demonstrates the use that can be made of the information contained in the code, and the interactive aspectprovides explicit training that is constantlyadjusted to the level of the learner. To obtain information on the relative importanceof thesethree aspectsof input on learning in a mimetic species,I used three different conditionsto train two juvenile Grey Parrots(Psittacus erithacus) to produceEnglish labelsto identify various commonobjects. Each bird experienced:(1) audiotapedtutoring, which was nonreferential, noninteractive,and did not demonstratecontextual applicability; (2) videotapes,which pro- vided reference and limited information about context, but which were noninteractive; and (3) live human tutors, who interactivelymodeled the meaning and use of the labelsto be learned.The birdslearned only from the live tutors.A third parrot,trained on a separateset of labelsby tutorswho provided only limited referenceand contextfor thosevocalizations, learnedto producethat setof labelswithout comprehension.The data suggestthat, even for birds known for their mimetic abilities, social interaction, reference, and full contextual experienceare important factorsin learning to produceand comprehendan allospecificcode. Received22 April 1993,accepted 10 October1993. IN THE LASTDECADE, studies have shown how rot (Amazonaochrocephala), and a Grey Parrot input affectsallospecific avian vocal learning (Psittacuserithacus) that experiencedlimited so- (review in Pepperberg 1991, 1993). For birds cial input (Mowrer 1952, 1954, 1958). In con- that favorconspecific learning (i.e. typicallydo trast, Grey Parrots that received modeled, in- not mimic otherspecies in the field), allospecific teractivehuman tutoring (Todt 1975,Pepperberg learning is often affectedby variationin social 1981, 1990a)acquired the targetedspeech pat- and environmental input. Such species(e.g. terns. Given the reputed easewith which these White-crowned Sparrows [Zonotrichialeuco- mimeticbirds are assumedto acquireany type phrys],Baptista and Morton 1981, Baptistaand of sound (see Amsler 1947), data on the effects Petrinovich 1984, 1986; Song Sparrows[Melo- of differentialinput were surprising.However, spizamelodia], Marler and Peters1977, 1987, Bap- becausedifferent laboratories tested separate sets tista 1988) may require visual and vocal inter- of conditions,the findings could have been a actionwith a live tutor for completeallospecific consequenceof interlaboratoryvariation, as well songlearning to occur.Less is known, however, as of the different learning conditions (Slater aboutthe effectof input on vocallearning in 1991). birds that are frequent mimics. The possibleconfounding factor of interlabo- Data on vocallearning in somemimetic birds ratory variation was counteredin a single study comefrom experimentson training thesebirds on mimetic EuropeanStarlings (Sturnus vulgaris) to reproducehuman speechin the laboratory that examined how competing forms of differ- (reviewin Pepperberg1988a). Little or nothing ential input affectedlearning (West et al. 1983). was learned by Indian Hill Mynahs (Gracula Sevenbirds, placedin three different groups, religiosa)exposed to tapes in social isolation did or did not experience, in various combi- (Grosslightet al. 1964,Grosslight and Zaynor nations:human care and vocal interaction; tapes 1967,Gossette 1969) or by an Indian Hill My- of humanspeech and whistles;and living quar- nah,Budgerigars (Melopsittacus undulatus), Black- ters sharedwith Brown-headed Cowbirds (Mol- billed Magpies(Pica pica), a Yellow-headedPar- othrusater) or other juvenile starlings.All birds 3OO April 1994] GreyParrot Vocal Learning 301 learnedvocalizations only from organismswith plicable, and noninteractive input; (2) refer- which they could interact (either human or ential, minimally contextuallyapplicable, and cowbird) or learned soundsclosely associated noninteractive input; and (3) referential, con- with the presenceof such organisms(e.g. the textually applicable,and interactive input. In opening of a door that preceded a morning the experimentwith the adult parrot, I studied greeting)and learned nothing from any non- the effect of input that was sociallyinteractive interactive source. Such data demonstrated the but that minimized reference and contextual effectof differentialinput on learning,but did applicability.At the time, I chosenot to study not isolatewhich aspectsof the input were crit- the effect of input that was referential, fully ical for learning. contextuallyapplicable, and noninteractivebe- To demonstratethe relative importance of causestudies on other speciessuggested that variousaspects of input for learning, one must suchconditions lead at bestto productionwith- first identify the relevant aspects.According to out comprehension(see Savage-Rumbaughet a psychologicalconstruct called "social-mod- al. 1980a, b). eling theory" (Bandura 1971, 1977), input can The resultsof theseexperiments not only pro- be characterizedby three main aspects(Pep- vide informationon Grey Parrots,but alsosug- perberg 1985, 1988b, 1991, 1992a, Pepperberg gestintriguing parallels between avian and hu- and Neapolitan 1988,Pepperberg and Schinke- man exceptional learning--learning that is Llano 1991):(1) degreeof referentiality,(2) scope unlikely in the normal courseof development of contextualapplicability, and (3) extent of so- but that can occur under certain conditions cial interaction.Reference and contextualap- (Pepperberg 1985, 1986, 1988a, 1993). Such be- plicability refer to the real-world useof the in- havior was first describedby human socialpsy- put, and socialinteraction is a potent meansof chologists (Bandura 1971, 1977). I discussthe highlightingvarious components of the input. resultsin the contextof my previousproposal Referenceis generally defined as the meaning that avian acquisitionof an allospecificcode is of an utterance(e.g. the relationshipbetween a particular form of exceptionallearning; I sug- a label and the objectto which it refers).Con- gestpossible parallels between such psittacine textual applicabilityinvolves the particularsit- learningand anotherform of exceptionallearn- uation in which an utterance is used and the ing, human second-languageacquisition (Pep- effectsof using the utterance. Social interaction perberg and Neapolitan 1988). actsto signal which componentsof the envi- ronmentshould be noted,emphasizes common attributes--and thus possible underlying METHODS FOR EXPERIMENT 1 rules--of diverse actions,and allows input to SUBJECTSAND HOUSING be continuouslyadjusted to the level of the learner.Interaction may alsoprovide a contex- Subjectswere juvenile Grey Parrots, Alo (female) tual explanation of the reasonsfor the actions and Kyaaro (male), that were 10 and 6.5 months, re- and demonstratethe consequencesof the ac- spectively,at the beginning of the experiment.They were hand raised and had been obtained from their tions (for detailed discussionof these points, breeder three months previously. They lived in sep- see Pepperberg1993). Researcherscan specifi- arate roomsand could not hear one another. Training cally design input that varies with respectto with live tutorsand testingoccurred while thesebirds theseaspects and then evaluatethe relativeef- were atop their cages,on "gyms" (branchesthat had fects of such variation. been nailed together),or on parrot stands.Birds were To carry out such an evaluation, I designed confined to Hoei cages(ca. 38 x 71 x 56 cm) when experimentsfor one adult and two juvenile Grey humanswere absent,and during sleepinghours. Wa- Parrots.I examinedhow variousforms of input ter and Harrison's Bird Diet were available continu- affectedthe amountand type of their acquisi- ously;fruit, vegetables,dried pastasand cerealswere tion of an allospecificcode, English speech. I provided when neither testing nor training were in studiedhow input might affectcompetence not progress. only with respectto physicalproduction, but TRAINING PROCEDURES alsowith respectto comprehensionand appro- priate use.In the experimentwith the juveniles, To provide input that varied with respectto social I studied the relative effectsof three types of interaction, reference, and contextual applicability, I input: (1) nonreferential, not contextuallyap- contrastedsessions of live, videotape, and audiotape 302 IREhIEM. PEPPERBERG [Auk, Vol. 111 T^BLœ1. Componentsof different types of tutoring Unlike othermodeling procedures (e.g. Todt 1975, used to train Alo and Kyaaro. Goldstein 1984), my protocol requiresrepeating an interactionwhile reversingroles of the humantrainer Contextual Social and model/rival, and includesthe parrot in the in- applica- inter- teractions.Thus, birds do not simply hear stepwise Reference bility action vocal duets, but observeand learn to engage in a Audiotapes No No No communicative process(i.e.