The Condor 96:70-X2 0 The Cooper Ornithological Society 1994 THE CHICK-A-DEE CALL SYSTEM OF THE MEXICAN CHICKADEE’ MILLICENT SIGLER FICKEN Department of BiologicalSciences, University of Wisconsin-Milwaukee,Milwaukee, WI 53211 ELIZABETH D. HAILMAN Department of Dairy Science,University of Wisconsin-Madison,Madison, WI 53706 JACK P. HAILMAN Department of Zoology, Universityof Wisconsin-Madison,Madison, WI 53706 Abstract. Chick-a-dee calls of the Mexican Chickadee (Parus sclateri)are composed of combinations of three common note types (A, C and D) and one very rare type (B). Calls have the invariant sequenceof notes A-B-C-D, where any note type may be omitted, given once or repeated a variable number of times before transiting to the next type. The B and C notes are phonologically similar to the B and C notes of chick-a-dee calls of the Black- capped Chickadee (P. atricapillus), but the A note is markedly different and the D note somewhat different from equivalent notes of the congener.A total of 2,07 1 calls recorded yielded 60 different call types,and Zipf-Mandelbrot plots show that the call systemis “open”; as the sample size is increased new call types will be found without demonstrable bound. In relatively undisturbed contexts (with mate on territory, in fall flocks, alone in fall) birds gave mainly [A][D] calls with lesser numbers of [A] and [C] calls, where brackets indicate variable repetition of note types. In disturbed contexts(mobbing plastic Great Homed Owl, mobbing speakerplaying calls of the Northern Pygmy-Owl, observer sitting under the nest cavity) the birds gave more [C] calls with [A][C] as well. In the longestmobbing sessionto owl calls, birds gave mainly [A] calls when approaching,switched to [C] calls while flying about the speaker,and then resumed[A] callsand moved offwhen the playbackwas stopped. Outside of human language,this is the second truly combinatorial system of vocal com- munication found in animals, the first being chick-a-deecalls of the Black-cappedChickadee. This studyprovides the first data substantiatingquantitative differencesin caikfrom different contexts,an important step toward understandingwhat kinds of information combinatorial chick-a-dee calls encode. Kev words: Parus sclateri: Mexican Chickadee;vocalizations; calls; syntax; mobbing; flocks. INTRODUCTION ture of the Mexican Chickadee’s calls, (2) com- All tit speciesof the subgenusPoecile (genusPar- paresthese results with those from Black-capped us) appear to give combinatorial “chick-a-dee” Chickadees, and (3) documents differences in calls (Hailman 1989) but this complicated call calling in different contexts. system has heretofore been analyzed quantita- Chick-a-dee calls are of special interest be- tively only in the Black-capped Chickadee, P. cause these compose the only presently docu- atricupillus (Hailman et al. 1985, 1987; Hailman mented combinatorial system of animal com- and Ficken 1986). Chick-a-dee calls of the Mex- munication outside of human language. The ican Chickadee (P. sclateri) were first recorded Black-capped Chickadee uses four note types by Dixon and Martin (1979) whose spectro- (Ficken et al. 1978) in combination to createhun- grams (their figures la and b, p. 422) show two dredsofdifferent call types (Hailman et al. 1985). kinds of notes. Ficken (1990a) found that in a The note types (designatedA, B, C and D) occur sample of over 1,000 recorded calls, four types in the fixed sequenceA-B-C-D, where any note of notes were given but one of them only rarely type may be omitted, given once, or repeated a (seealso Ficken and Nocedal 1992). The present variable number of times before transiting to the study, based on further field work including next note type within the call. This straightfor- mobbing experiments, (1) describes the acous- ward phonological syntax was shown to be log- tical features and analyzes the syntactical struc- ically explicit by writing a “characteristic func- tion” (correctly working algorithm) for a Turing machine (Hailman and Ficken 1986). However, ’ Received 12 March 1993. Accepted 9 August 1993. systematic departures from first-order Markov [701 MEXICAN CHICKADEE CALLS 7 1 chains of transitions between note types show (150 Hz filter band width). Note types (described that far more complicated rules underlie the pre- in the Results) were classifiedby eye and written cise structure of calls (Hailman et al. 1987). De- on data sheets.In all, 2,045 calls were analyzed spite extensive analyses of syntactical structure, (a few occurredin other contextswith insufficient the communicative significance of chick-a-dee sample sizesfor analysis). Data on the note com- calls remains elusive. The present study of the position and context of each call were read into Mexican Chickadee provides not only the first a database and made accessibleto mainframes comparative data on syntax in another species and microcomputers for analyses.Analyses were but also an important first step toward under- basically a subsetof those performed on calls of standing differences in calls in different behav- Black-capped Chickadees by Hailman et al. ioral contexts. (1985) designed by J.P.H. and programmed by E.D.H. Most of the special analytical programs METHODS were written in PASCAL and run on microcom- All recordingswere made at or in the vicinity of puters. Rustler Park in the Chiricahua Mountains (Co- Contingency tables were analyzed statistically chise County) in southeasternArizona. Record- using “computer-intensive” methods of the pub- ings were made by M.S.F. in October 1985, and licly available software MONTE CARLO RXC May and October 1986 (Ficken 1990a); further written for the Apple Macintosh by W. R. Engels field work by the three authors togetherwas con- of the University of Wisconsin-Madison, De- ducted in April 1990 and March 199 1, by M.S.F. partment of Genetics. Such analyses provide a in May 199 1, and by the three authors together more sensitiveand accurateassessment than Chi- in April 1992. square methods often applied to such data (En- Calls were divided into four principal contexts gels 1988). At least 1,000 trials were run for a of recording: (1) with mate on the breeding ter- given test to createthe distribution against which ritory, (2) in mixed-species flocks in the fall, (3) the data were compared. Sequential analysis by when disturbed by the presence of an observer the method of Markov chains was done with near the nest, and (4) when mobbing a speaker UNCERT, publicly available software for DOS playing the call of a Northern Pygmy-Owl, Gluu- computers copyrighted by E.D.H. and J.P.H. cidium gnoma. In addition, small samplesof vo- calizations were taped in two other contexts: (5) RESULTS lone birds in the fall and (6) mobbing a plastic model of a Great Horned Owl, Bubo virginianus. PHONOLOGY The mobbing experiments using owl tapes were Chick-a-dee call systemsas a whole are doubtless conducted at five different sites. The partially homologousamong speciespossessing them. Two diurnal Northern Pygmy-Owl takes small birds of the Mexican Chickadee’s note types differ and is common in the study site; during one ex- somewhat in acoustical structure from those of periment, an owl answered the playback from the Black-capped Chickadee, so they might not acrossa canyon. In two experiments tapes were be homologous. Unlike the basically chevron- played back from a Marantz PMD 430 Profes- shaped A note of the Black-capped Chickadee, sional cassetterecorder through a Realistic Min- the Mexican Chickadee’s A note (Fig. 1) is fre- imus-0.6 amplified speaker near the ground on quency modulated at a high rate, giving it a buzz- a log or stump. In the other three experiments, ing aspectto the human ear. Buzzing notes char- tapes were played back from a Sony Walkman acterize other vocalizations of the Mexican Professional cassette recorder through a Sony Chickadeeas well (Dixon and Martin 1979; Fick- SRS-27 amplified speaker.All playbacks attract- en 1990a, 1990b). The A note usually sweeps ed a number of small forest speciesbesides Mex- downward in frequency during its duration (Fig. ican Chickadees. 1) but the magnitude of the decline is variable. Most of the recordings were made on a Sony Dixon and Martin (1979, Fig. 1a) showed a call Walkman Professional cassette tape recorder with three A notes that lacked this frequency (details in Ficken 1990a, 1990b), with further downsweepcompletely, and there seemsto be a recordings of mobbing experiments made with continuum in the slope of the downsweep. The a Sony 8 mm camcorder. Tapes were analyzed A note was common (1965 notes recorded),com- by M.S.F. with a Kay 7800 Digital Sona-Graph prising 28.4% of all notes. \ 1 72 M. S. FICKEN, E. D. HAILMAN AND J. P. HAILMAN a 0 0 0.5 1 1.5 Time (s) C d 8 6 4 2 0 0 0.5 1 Time (s) FIGURE 1. Sound spectrogramsillustrating the A and D notes of chick-a-dee calls of the Mexican Chickadee, selectedto illustrate some of the phonologicalvariation found in notes. The frequency and time scalesare the same for all spectra.(a) Commonest of all calls is the call type AD, with typical down-slurred A note. Notice the banded structure of the D note. (b) A call showing the typical A/D contraction of the final A and first D notes of calls containing both types. (c) The contracted A/D may begin a call; notice the noisy (unbanded) structureof the D notes. (d) Rare phonologicalstructures occur, as in this call with an A-like introductory note followed by an A/D-like structure of long A component and short D component. MEXICAN CHICKADEE CALLS 73 TABLE 1. Durations, highest frequencies, and lowest frequencies of note types in chick-a-dee calls of the Mexican Chickadee.