Fig. 1

Response of the horses to the playbacks. Scores of the second principal component (PC2) of the principal component analysis as a function of the four playback treatments (familiar (white)/unfamiliar (grey) * separation (-)/reunion (+); box plot: the horizontal line shows the median, the box extends from the lower to the upper quartile and the whiskers to 1.5 times the interquartile range above the upper quartile or below the lower quartile; open circles indicate outliers and black circles the mean; the grey lines show the model estimates (continuous line) and 95% confidence intervals (dashed lines)). More positive PC2 scores corresponded to horses that moved their head more, had their head high for a longer duration, responded faster and had a slower respiration rate (Table 2) (Tukey post-hoc test: * p < 0.05, NS = Non-Significant)