How to stop them from doing this?

[wingsofglory]

There is another thread - someone else is finding her Tetra Tints are pecking flock members to death and eating them! Its been one or two a night, she finds the dead ones in the morning. Its not predators. She sees where the Tetras have started holes in a bird, then continue till its dead, if she doesn't get there in time.

I'd try supplementing plain cooked cod or some other cheap fish.