It might be that the window behind the box is tinted so that movement won't disturb the birds ... but you are right, it is an interesting design - going to keep a copy of the photo showing the nestbox and ledge in case we ever have a site with a similar design.
What's nice is that it gives the chicks the option to hop through the "backdoor" onto the ledges beside the box, it doesn't look like they can do that from the "front". And it certainly would give project staff access to the chicks when necessary - and because the adults are used to the backdoor it could be less stressful for them if someone did need to access them that way ...
