This is a first-time problem. Parents and previous chicks' feathers have always been in a very good condition. I can't get a blood sample because the chicks have been destroyed. The hen has started breeding again and has three eggs. Calcium powder is provided to the breeding pair at this stage, over the food twice a week.
Food is a normal seed mixture, with fruits and vegetables always available.
Thank you for the extensive history on the parents and the aviary concerned, as this makes the interpretation of the problem easier. However, it is a pity that the affected birds were not examined or that samples were not taken for testing, as this would have provided a diagnosis. Of course, this is a non-infectious problem, but it is important that you determine which parent did the plucking. This can occur out of the blue in birds that have previously reared normal young. Circovirus or Psittacine beak and feather disease virus is the other possible cause, and is much more serious.