Concerned with z. finch health

Question
Hello,
I have had a pair of healthy male zebra finches for 1.5 years now and I decided it would be great to introduce a pair of female zebra finches. Its been a few days since I've added the female pair. I suspect the males may have caught a disease/parasite/lice? One male seems unusually more sleepy and tucks his head in his feathers at random intervals of the day. The clan is continuously picking at their feathers (more than what I have observed in the past) and persistently wipe their beaks and heads on the branches (more so lately). I also found a bald spot on one female's back but I have not observed the males or the females doing any plucking. Should I be concerned? Is this an indication of ill-health?I change the feed and water supply everyday.

Answer
Sounds like you may have feather mites; these mites can be indirectly deadly. They bother the bird night and day and keep them awake. The best way to tell is to take a bird and open one of the wings and look at the feathers. If they have holes or are tattered and ill-kept then you know that they have feather mites. These are easy enough to get rid of using supplies from www.ladygouldian.com or www.ladygouldianfinch.com.

The other thing that they may have is air sac mites; these mites live in the throat and lungs of the bird. They can multiply to the point where no air gets into the lungs and the bird slowly suffocates. This is can and will be fatal if not caught in time. There are two ways to tell. The first one is to soak the bird's neck in water and shine a powerful light through it. If you see something you know shouldn't be there then they have air sac mites. The other way to tell is to hold the bird up to your ear and listen for clicking (I prefer this method over the other. I'm too worried I may accidentally injure the bird). If you heard clicking they have mites. The more clicking, the more mites.
Thankfully this is also easily treated when caught in time (sounds like you have caught it in time). The sites above have a medication called "Scatt". It's similar to Ivamech (used on larger animals when they have parasites) but can be used on finches (when it comes the Ivamech, the cure is worse than the disease and can kill finches easily). Do not got with S76 which also states it helps with air sac mites. You'll want the Scatt so you know for a fact that the bird has been medicated.