I believe many folks will say 100ft minimum. That being said, my quail are in cages on the ground in my yard and my chickens and ducks walk all around the quail cages. My chickens will even jump on top (cages are 2ft tall). I did lots of reading and knew the risks beforehand. I don't have enough space to keep the chickens that far away, especially since I added three grow out pens throughout my yard. I choose to take the risk and have them living very closely. So far I have not had any sick quail. I believe that part of the reason my quail haven't gotten sick is because they are on dirt; living in cages with lots of hiding places (equals less stress). I think these factors have helped my quail build stronger immune systems. I know there is still a chance they can get sick but I am happy with my choice.