It's difficult to examine the birds with a flashlight that is why I wear a head lamp so I have both of my hands free to inspect the birds. Take some paper towels out in the evening and wipe the roosts especially under them and look for streaks on the paper towels. That is usually a sign there...
I had some birds that looked very similar to the ones in the pictures. When I checked them during the day I didn't see anything on them but when I check them after they roosted they were loaded with mites. I'm not saying that's what it is but I would still check. Again, good luck...
:welcome :frow Are you sure they don't have mites? First you need to determine if you have mites. Some mites only come out at night to feed on the birds. I use a headlamp so I have both hands free to check over the birds after they roost. I have a lot of birds. I had a mite infestation in one...