Iris is starting to feel eggy. She's started sitting in her nest now, and for longer periods of time. I haven't noticed many belly feathers falling out yet, but that may not start until just before the first egg.
In this video Rusty brings food to Iris, which she eventually accepts. She doesn't eat it, but instead flies to the hatch perch to cache it, then returns to sit on the nest. She will stop eating or eat very, very little before laying eggs. There's only so much room in a bird's abdomen when you need to stay light in order to fly. So not eating could indicate eggs are on the way.