Dry spring weather ( such as we had last year) is a disaster for swallows who return to the UK to breed and then desperately need soft mud to make their nests. If mud is not readily available,these durable boxes that closely resemble the nests they build themselves are the next best thing - and they will adopt them for breeding.
Allow at least 1 metre between these nests. Swallows are semi-sociable and don't like to be crowded out ( a bit like myself !) These nests should be positioned inside sheds, stables and barns and please make sure there is access through a window or opening.