Social Scene
Turkeys are a very social species. A single bird doesn’t do well alone and will attach to another species in close proximity. However, a mixed flock of turkeys and chickens isn’t a good idea, as each is susceptible to adverse reactions to diseases that each species may carry.
An immunity to a parasite or bacteria that a chicken may have and yet carry can harm and even kill a turkey, which has no such immunity. Even housing turkeys in quarters once occupied by chicken flocks can result in sick birds, stunted growth, and even death.