Table 2 Experiment 2: Subjects’ vocal, nonvocal, and monitoring behavior at snake models is best explained by the receiver knowledge, not signaler habituation, hypothesis.

Experiment 2: Subjects’ vocal, nonvocal, and monitoring behavior at snake models is best explained by the receiver knowledge, not signaler habituation, hypothesis.. Subjects’ overall responses across all tests differed significantly across conditions (permutation test correcting for multiple testing: χ² = 62.47, P = 0.004). Parentheses denote the variable level that reflects the estimate when tested against the alternative level. GLMMs: H1 (receiver knowledge), supported or tentatively supported by models (B) to (H); H2 (signaler habituation), not supported by models (B) to (H). n = 10 subjects, 21 trials, and 12 dyads. Bold: P < 0.05; italic, P < 0.1. Test predictor for all models, experimental condition (rest hoo and alert hoo). Random factors for all models include subject identity, dyad identity of subject, and call provider. Binomial, models (B), (E), and (F); Gaussian, models (A), (C), (D), and (G) to (I). Model significance versus null model, effect size (marginal R2): (A) χ² = 10.31, df = 1, P = 0.006; R2 = 0.16; (B) χ² = 6.7, df = 1, P = 0.009; (C) χ² = 3.12, df = 1, P = 0.077; R2 = 0.30; (D) χ² = 3.96, df = 1, P = 0.046; R2 = 0.32; (E) variable “alone” excluded due to model stability: χ² = 7.89, df = 1, P = 0.005; (F) χ² = 9.9, df = 1, P = 0.002; (G) χ² = 6.4, df = 1, P = 0.25; R2 = 0.26; (H) χ² = 2.65, df = 1, P = 0.10; R2 = 0.17; (I) χ² = 6.9, df = 1, P = 0.0085; R2 = 0.41. For models (C) and (D), cases containing zeros were excluded; thus, P values are likely affected by low power (see Fig. 4, C and D, for paired data plots, table S2 for source data, and table S4 for additional analyses of control variables).

Response variablePredictor variableβSEχ²PH1H2
Calling and marking behavior
A. Number of calls emitted*Intercept0.620.27
Condition (rest hoo)0.560.186.730.009YesYes
Alone (yes)0.030.380.010.94
B. Call or notIntercept11.238.08
Condition (rest hoo)15.0310.283.030.082(Yes)No
Number of alert hoos played−0.132.970.0020.97No
C. Latency to first call*Intercept1.660.41
Condition (rest hoo)0.850.463.120.077(Yes)No
Alone (yes)−0.770.432.880.090
D. Median inter-call interval*Intercept8.655.96
Condition (rest hoo)12.666.653.960.046YesNo
Alone (yes)−9.126.282.430.12
E. Call and mark co-occurrenceIntercept−10.836.02
Condition (rest hoo)20.288.337.890.005YesNo
F. Mark or notIntercept−10.05.14
Condition (rest hoo)20.107.729.860.009YesNo
Alone (yes)−0.264.900.0030.96
Attentional state
G. Scans to speaker/s: Post/prior seeing the snakeAlone (yes)0.500.20
Condition (rest hoo)0.460.166.420.011YesNo
Alone (yes)−0.250.280.770.38
H. Looking duration to the snake before first looking awayIntercept1.770.22
Condition (rest hoo)0.380.252.650.11NoNo
Alone (yes)−0.240.251.100.30
I. Scans to speaker/s after playback before the snakeIntercept0.530.086.910.009
Condition (rest hoo)0.260.08
Alone (yes)0.170.092.600.107

*Transformation, log + 1.

†Confirms results of previous study but does not discriminate between hypotheses.