Research ArticleECOLOGY

Tool-assisted rhythmic drumming in palm cockatoos shares key elements of human instrumental music

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Science Advances  28 Jun 2017:
Vol. 3, no. 6, e1602399
DOI: 10.1126/sciadv.1602399
  • Fig. 1 Palm cockatoos use sound tools to produce a rhythmic beat.

    (A) Male palm cockatoo drumming on a hollow tree with a manufactured “drumstick.” Photo: C.N.Z. (B) Distribution of variances for intertap intervals (seconds) over 131 sequences of drumming by 18 male palm cockatoos. (C to H) Examples of drumming sequences of varying length showing time on x axis (seconds). Temporal spacing of drumming taps is shown in the top row of each figure and is compared to a randomly generated sequence in the lower row. Sample sizes, mean intertap intervals, coefficients of variation (cv), and shape parameters are given above each sequence.

  • Fig. 2 Individual drumming styles of male palm cockatoos.

    (A) Log of shape parameter ν ± SEs for the intertap intervals of 18 male palm cockatoos. (B) Log of mean intertap interval versus log variance for 131 sequences across 18 male palm cockatoos. Three males are highlighted: male 2 (green) illustrating a consistently faster drumming rate with higher variance, male 10 (red) showing slower drumming rates, and male 17 (blue) showing mostly slower drumming rates with occasional sequences of faster drumming. The line illustrates expected values from the Poisson process, where the variance and mean are equal.

  • Table 1 Descriptive data for seven drumming sequences with >25 beats.

    Sequence number, mean and SD of the interbeat interval, and total number of beats in the sequence are shown. χ2 statistics and P values for a global test of autocorrelation in each sequence (testing for autocorrelation up to 10 lags) and a test of autocorrelation at the first lag, together with the number of beats over which significant autocorrelation was detected, are also given. Sequences were performed by male 17 (30, 49, 50), male 10 (112, 120), male 8 (6), and male 2 (88).

    SequenceMean interbeat
    interval (s)
    SDTotal number
    of beats
    Global test of
    autocorrelation (χ210)
    PAutocorrelation
    at first lag (χ21)
    PAutocorrelation
    for next n beats
    300.920.179236.2<0.00121.5<0.0012
    490.940.185121.30.0207.60.0061
    500.840.294371.3<0.00125.6<0.0015
    1200.890.164221.60.02017.0<0.0011
    60.710.183849.8<0.00125.5<0.0013
    880.470.17312.90.9800.930
    1120.830.10273.40.970.30.580

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1602399/DC1

    fig. S1. Typical drumsticks manufactured by palm cockatoos (left) and a modified seedpod (right).

    fig. S2. Sound properties and spacing of drumming.

    fig. S3. Log of mean intertap interval versus log variance over 131 sequences of drumming by 18 male palm cockatoos.

    fig. S4. Correlograms for seven longest drumming sequences.

    movie S1. A male palm cockatoo drumming on a nest hollow using a seedpod.

    movie S2. A male palm cockatoo drumming on a hollow tree stump using a drumstick fashioned from a tree branch.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Typical drumsticks manufactured by palm cockatoos (left) and a modified seedpod (right).
    • fig. S2. Sound properties and spacing of drumming.
    • fig. S3. Log of mean intertap interval versus log variance over 131 sequences of drumming by 18 male palm cockatoos.
    • fig. S4. Correlograms for seven longest drumming sequences.
    • Legends for movies S1 and S2

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). A male palm cockatoo drumming on a nest hollow using a seedpod.
    • movie S2 (.mov format). A male palm cockatoo drumming on a hollow tree stump using a drumstick fashioned from a tree branch.

    Files in this Data Supplement: