Differences within and among individual flies. (**a**) The first and second halves of trajectories for three male and three female flies from the same trial. (**b**) Scatter plots of walking statistics from each individual fly in the first 15 minutes of its trajectory against the same statistics from the last 15 minutes of its trajectory for flies in all trial types (female *n* = *132*, male *n* = *159*). M = male, F = female, B = both male and female. Walking statistics examined were: (*left*) Mean speed in frames in which fly was classified as walking: *r* = 0.889, *P* < 2.2 × 10^{-16} (*r*, Pearson’s correlation coefficient; *P*, the probability that the null hypothesis of *r* non-positive is correct), (*center*) Fraction of frames fly is classified as walking: *r* = 0.689, *P* < 2.2× 10^{-16} (*right*) Mean duration of sequences of consecutive walking frames: *r* = 0.765, *P* < 2.2× 10^{-16}. (**c**) Chasing behavior differences. We repeated the above procedure for chasing behavioral statistics: (*left*) Frequency with which the fly begins chasing another fly: *r* = 0.592, *P* = 3.89× 10^{-16}, (*center*) frequency with which a fly is chased by another fly: *r* = 0.213, *P* = 1.54× 10^{-03}, and (*right*) mean duration of chases: *r* = 0.054, *P* = 0.261.

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