The Common House Martin - Delichon urbicum, is a migratory swallowwhich breeds in Europe, North Africa and temperate Asia and winters in sub-saharan Africa and tropical Asia. It feeds on insects which are caught in flight, and it migrates to climates where flying insects are plentiful.

According to Martin Goodey there were large numbers of House Martins on the Isles of Scilly, South Western part of UK on the 25th May 2011.

"House Martin, currently estimate something like three or four hundred across all Islands, unusual to have so many lingering at this time of year. Speculation - standing on the road at Porth Hellick last evening waiting for the Red-rumped Swallow, in the end, I had to pack up and go home. Driven away by the sheer number of biting midges! Never known
anything like it even in the tropics. The House Martins may be taking advantage of this super abundance and be reluctant to leave.

Barn Swallows - good numbers present although I suspect many fewer now stay to breed.

Unfortunately as a result of the success of House Sparrows (Scilly probably has highest density anywhere in UK) House Martins have a very hard time of it. Only yesterday a friend proudly showed me a nest on his house and as we were watching a male House Sparrow stuck his head
out. Shame.