I'm in a turkey producing area - one of the largest in the country. What helped massively in 2015 was to simply put fine netting over the windows to the turkey barns, keeping other birds and at least some of their excrement out.
This is from Australia, but whatever:
"In Australia, indoor and free-range poultry, are at risk of contracting avian influenza due direct and indirect contact with waterfowl who may carry avian influenza virus in their nasal and eye discharge or faeces, farming and biosecurity practices.
Indoor (barn or shed) systems limit poultry from direct exposure to wild birds, but these are not immune to avian influenza risks due to indirect contact. This is because equipment, vehicles and human movements between farms can introduce the virus indoors, in particular when on-farm dams or open water sources act as a permanent residence for waterfowl.
Birds with outdoor access (free range) are at risk of coming into direct or indirect contact with wild waterfowl. Vegetated range areas may attract waterfowl, in particular if poultry are given feed or water outdoors. In free-range production systems, producers should therefore focus on managing these systems to reduce the risk of avian influenza."
https://kb.rspca.org.au/knowledge-base/what-is-the-risk-of-f...