The red mites appear at night and suck the blood of birds. You can test for red mites by sliding the blade of a knife in a crack or crevice. If the knife has blood on it when you withdraw it, you have mites. Another way to test for mites is by leaving a crumpled white cloth overnight in the birds' quarters. If you can see bright-red tiny spots on the cloth when you check it the next day, these are mites.
Mites love warmth, unpainted woodwork, and the more crevices the better.
When constructing an aviary shelter, keep this in mind. Putting filler in cracks and crevices is a laborious, but sensible precaution. If you have sucking mites, you will have to treat the birds and their surroundings. The insecticide Pyrethrum powder is usually effective, but any good pet store will advise you on a suitable powder. Even if you do not think you have mites, dusting nest pan liners used by canaries or other finches with an insecticide powder is a good precaution against sucking mites.