Zebra Finch Deaths

Question
I have had all but two of my eight finches die. The pet store said "draft" but I have my two big cages covered partially to prevent that. Also my two breeding adults have already gone through one winter in this house. Should I not put any birds in the empty cages? I'm at a loss and sad because I love my birds. I still have a mated pair of Zebras in another cage and two Canaries, yet I cannot take a chance on losing them. Please answer.....and thank you.

Answer
Drafts can kill birds but so can too low a temperature. I highly doubt that this was the cause of death though. The most common killer of finches is Sac Mites; and pet store birds are usually crawling in the little buggers. Sac Mites are little mites that live in the lungs of the bird and survive off the bird's blood. That in itself doesn't kill the bird. What does is the population, mites reproduce quickly and can just as quickly suffocate the bird. However, there is an easy way to tell of your bird has sac mites, hold the bird up to your ear (make sure there's no other noise around you) and listen for clicking. If the bird clicks while it breathes, it's Sac Mites. If this happens to be the case, let me know and I will tell you the VERY simple solution to getting your bird healthy. If not, contact me again with as much information on the following:
what food they eat
how often the food is changed
how often the water is changed
how often the water dish is cleaned
how often the bottom of the cage is cleaned
what is used on the bottom of the cage
overall temperature of the cage
location of the cage
how often the cage and it's contents are sanitized

And really, any other information you think will be helpful will help out a lot should Sac Mites not be the culprit