In field, one can observe without difficulties that two flocks are intersected or combined with each other. For
example, a fish flock in a stream separates into two part by obstacles (e.g. stone) and rejoins behind the obstacles.
The dynamics of two flocks guided by their leader were studied in the situation where the flocks cross each other
with a crossing angle, ？？, between their moving directions. Each leader is unaffected by its flock members whereas
each member is influenced by its leader and other members. To understand the dynamics, I investigated the order
parameter,？？, defined by the absolute value of the average unit velocity of the flocks’ members. When the two flocks
were encountered, the first peak in？？ was appeared due to the breaking of the flocks’ momentum balance. When
the flocks began to separate, the second peak in？？ was observed. Subsequently, erratic peaks were emerged by some
individuals that were delayed to rejoin their flock. The amplitude of the two peaks, d1 (first) and d2 (second), were
measured. Interestingly, they exhibited a synchronized behavior for different ？？. This simulation model can be a
useful tool to explore animal behavior and to develop multi-agent robot systems.