Last night just the parent bird and the two swiftlets in box 2 roosted. Today, we had a visit to box 3 briefly, and now the bird is back again to roost. What a surprise ... it seems to have made itself comfortable and is sticking more feathers down in the nest. I have no idea whether this is one of the regular box 3 pair returned or if it's a new bird. It'll be interesting to see what happens tomorrow night!
Here is a closer shot of our box 3 bird looking quite at home in the nest.