Aggression to Chicks by Muscovy female

We have a wild flock of 40+ Muscovy ducks living on and around a large pond. Recently, one young female suddenly selected a young chick belonging to another female; grabbed it; and ran of with it, shaking it violently. She then ran to the pond and dragged the chick out to the middle and proceeded to shake, submerge, and drown it. The other ducks pursued her all the way but did not intervene. What is this behavior about? I've never seen this before.