We all have the heater on..
nice and warm but the birds are scratching themselves and keep preening...
In the tropics where they come from, this is something they do not know; sometimes there the humidity percentage is as high as 90-95%.

Due to the dry air from the central heating, the skin (and feathers) do not get enough moisture.
Just compare it to the feeling when you've showered and your skin feels tight... 
Fortunately, there is a solution!

Spray the bird with boiled water so that the lime comes off and put it in the water bath
-one tablespoon of aloe vera juice (99% pure) added to 1 liter of water 
 -of unscented bath salt 1 teaspoon per 1 liter of water
that keeps the skin and feathers supple and the bird(s) are back in their element!