According to the most authoritative book available on birds in the Western Isles House Martins do not seem to have nested in the Western Isles since an apparently unsuccessful attempt at breeding in 1974.
Imagine my surprise, therefore, when quite a few House Martins reconoitered the front wall of my house a few days ago with an obvious view to finding a nest site. After a few days of flying to and from exactly the same point on the wall they lost interest and returned to their habitat down towards the sea. One major problem for House Martins trying to nest on Lewis is the lack of mud. There is almost no clay on the Island and, as far as I am aware none at all near me.
The photos are taken through double glazing in less than perfect photographic lighting conditions.