My two older girls (both over a year old) have lost their feathers underneath on their abdomen. One is quite raw with it. They're not sitting on the nest for hours on end nor is there any evidence of mites and they're both laying normally - not every day but still often enough. I'm wondering if they might be going into their first moult? Their sister Margo died a few weeks ago, and two newbies joined a couple of weeks before that... could it be stress? Both of them?
Here's a couple of pics, hope someone can help

This is Jerry, the one with the raw patches

And this is Barbara, no red raw areas
ETA - just had a quick google read... Is it likely that they're bored? I have noticed feathers under the perch they both sleep on. Someone suggested that they might be too bored first thing in the morning waiting to be let out.
We had Margo in our bathroom for 3 weeks when she had a prolapse vent and she started to peck at her feathers during that time.
Do I simply need to let them out earlier?
