Figure 1. The top-ranking rooster in a group announces the break of dawn.

(a) Representative actogram of crowing behavior under 12 hour light:12 hour dim light (12L12dimL) and constant dim light (dimLL) conditions for one individual from one of three rooster groups. The light and dim light periods are indicated by yellow and gray backgrounds, respectively. (b) Higher-ranking roosters tended to crow more frequently than lower-ranking roosters under the 12L12dimL condition (F_3,8 = 6.8, P < 0.05, ANOVA, Tukey-Kramer’s test; mean + SEM, n = 3 groups). Different characters indicate significant differences. The data follows the normal distribution (χ² = 3.8, P > 0.05). (c) The first-ranking rooster started to crow first every morning (F_3,8 =124.0, P < 0.01, ANOVA, Tukey-Kramer’s test; mean + SEM, n = 3 groups). The data were arc-sin transformed before analysis and back-transformed data was shown in the figure. (d) Transition diagram of crowing order between social ranks showed that roosters start to crow in descending order of social rank. The proportion of the transition in relation to the whole is indicated by line weight. Significantly increased transitions are shown by black lines, with their proportion and significance (^***P < 0.001), and the other transitions are shown by light gray lines. (e) Lower-ranking roosters immediately followed the first-ranking rooster’s predawn crowing (mean ± SEM, n = 3 groups). (f) A strong positive correlation was observed between the timing of first crowing of the top-ranking rooster and those of its subordinates (1st and 2nd rank: R = 0.98, P < 0.01; 1st and 3rd rank: R = 0.85, P < 0.01; 1st and 4th rank: R = 0.78, P < 0.01, Pearson’s correlation). Time 0 indicates light-onset time.