That’s a reasonable design. The result would be interesting and may raise more questions than it answers. That is a good thing.

I don’t think this design would conclusively prove they were engaging in abstract communication, but that would take many experiments of similar scope.

A sceptic could say the unconditioned group reaction was a result of social awareness of the reaction of the conditioned crows. Sort of a collective freak out based on the immediate reaction of the marked individuals.

Regardless, I hereby tender my application to be colony manager of the research group. Murder Manager is the title I would choose.