If you don't find any mites on your birds during the day, I use a headlamp so I have both of my hand free after they roost, I go in and inspect the birds. You can take a paper towel and rub it on and under the roost and see what you get on the paper towel. Good luck...
Rub a paper towel under the roost.
Ok this is how dense I am, rub where how, I am picturing rubbing the paper towel through the nights droppings here.... or you talking the actual roosting bar itself? duuh yah I know dumb question. thanks tho for answering