Critiques of flock-level welfare metrics often argue that group averages hide the situation of individual animals. Here, we demonstrate that optical flow measures collected from broiler groups can yield information not only about mean flock activity but also about the distribution of movement types within the group. The mean reflects overall motion, while variance, skew and kurtosis capture differences among individuals. We linked optical flow statistics to the behavior and welfare of 16 sampled birds per flock using two runway tests and a water (latency-to-lie) assessment. In the runway tests, average completion time was positively associated with skew and kurtosis of day-28 optical flow (i.e., slower individuals typically came from flocks with elevated skew and kurtosis). In the water test, mean standing duration showed a positive association with mean and variance of flock optical flow (i.e., the most mobile birds usually derived from flocks with higher mean flow). Thus, flock-level patterns carry meaningful information about the activity profiles of different proportions of individuals.
