Fig. 1

(a) EOM frequency. Number of EOM events per day (i.e., 12 h; as this roughly corresponds to the wake time of a wild orangutan⁸⁶) as a function of age at both settings (wild: purple; zoo-housed: yellow). The points depict the EOM rate per a given age, per setting, and their area corresponds to the total duration of observations (range of actual observation durations per dot: 0.08 to 22.21 h). The dashed lines and shaded areas depict the fitted model and its 95% confidence limits. (b) EOM duration. Duration of EOM events as a function of age in wild (purple) and zoo-housed orangutans (yellow). The points depict the average duration of EOM events per age and setting and their area corresponds to the number of observations (range: 1 to 275).