Where did the swallows perch?

Good question from Henry J Place of Garan, Parteen, Co Clare

Good question from Henry J Place of Garan, Parteen, Co Clare. How did the swallows manage before the advent of overhead electric and telegraph wires? "I can only once recall seeing swallows perched on a tree (or dead tree). Perhaps you might care to muse on this matter some time." Well, on to Gilbert White (1720-93) and his Natural History of Selborne, the man who wondered if swallows spent the winter in the mud of the village pond. He has a note dated September 13, 1791: "The congregating flocks of hirundines on the church and the tower are very beautiful and amusing. . .The flight about the church seems to consist chiefly of house martins, about 400 in number, but there are other places of rendezvous around the village frequented at the same time. It is remarkable that, though most of them sit on the battlements and roof, yet many hang or cling for some time by their claws against the surface of the walls, in a manner not practised by them at any other time of their remaining with us."

And then to swallows, the subject of our friend's letter. "The swallows seemed to delight more in holding their assemblies in trees." And then Marwick, White's correspondent, adds a note. He first makes it clear that he is convinced that the hirundines in general simply migrate to other climes in the autumn. Too many of them have been seen in flocks by sailors crossing the seas. He notes that White's observation of the congregating of the birds on the roofs and trees as being similar to what happened in his own church at Catsfield.

You would be inclined to say, "Well, of course, they gathered on wire fences and indeed fences of other kinds, such as wood, though they would be near the ground and therefore nearer to predators like foxes and weasels." But were such fences in use at the time? Was there the same need to cut off each man's land? Surely the most obvious and, from the birds' point of view, if we can look into their minds, strong, relatively high and safe resting-places were the roofs of church and other strong buildings. Trees, dead and bare with clear vision would also be useful, but leaved trees?

Couldn't offshore islands like Skellig in our case, and others around these islands serve too? Anyone with other ideas?