Well, after replacing the dead camera with a working one we were surprised to find, that evening, that there is still a roosting bird in Box 3. It’s presumably the partner of the dead one and we think it must have been roosting on top of the dead bird. Very sad. It has been there for the last two nights, but I suspect that without a partner and any young to look after it will be away very shortly.
Here's a picture from last night
The pair in Box 1 continue to mess about, playing with the nest and sticking down feathers but as usual the eggs are rolling around elsewhere and it seems to be sheer luck if either of the birds happen to actually sit on them at all. Oh well, better luck next year!