Hi, I built a swift bird box 4 years ago to specifications I found on a swift conservation page. I hung it outside my 5 story window in Barcelona and waited. Years went by and nothing. But now this year a pair of swifts arrived a week ago (So mid June) and have been sleeping in the box each night but seem to be doing nothing in the way of building a nest (I have a little hole in the box where I can put in mobile phone and observe them). But they are in there every night and also dont seem to leave each morning until rather late (around 9am....most swifts seem to be out hunting insects in the early hours) All seems strange to me no? I thought they slept in the air and only went in to "roost" like that when they were about to lay eggs. Any thoughts on what they are up to? Thanks!