Nesting swallows

I'm delighted that swallows are nesting in one of the outbuildings. I realised last year that there were plenty of swallows but no nests on our land. To encourage them I installed four artifical swallow nests in outbuildings. Needless to say the swallows have totally ignored the nests I put up and built a makeshift nest resting on a girder. No pictures I'm afraid - I tried a flash assisted picture but it just frightened the fledgling who was sitting there and the photo didn't come out.