I had posted this article in the other thread but felt it has a lot of relevance. While it is only dealing with domesticated chickens and turkeys it seems it would be applicable in wild birds as well. Here are a few of the parts that stuck out to me.


It is commonly agreed that all broiler breeder farms are heavily contaminated with caecal worm (Heterakis gallinarum) eggs, which are the only known biological vector of the blackhead organism.


The life cycle of Histomonas has been reconsidered, after the discovery that turkeys could become infected from direct contact with other birds or contaminated faeces.


http://www.thepoultrysite.com/articles/1285/control-of-blackhead-disease/