Conflict with sparrows
While house martins are rarely affected by predation, house sparrows frequently damage or take over nests and attack adults, eggs and young.
Sparrows can be discouraged by placing a curtain of weighted strings in front of the nest. Sparrows find it difficult to fly up at a steep angle to the nest, but martins do so easily. The strings should be about 230 mm long, 65 mm apart and no nearer than 150 mm to the nest hole.
The strings should all be the same length to prevent tangling. They can be fixed with nails or drawing pins and weighted with steel nuts or plasticine. This curtain may be erected before the martins arrive but should only be put up during nest building if sparrows attempt to take over.
If house sparrows are keen to nest on your house, placing nestboxes with 32 mm entrance holes under the eaves well away from the house martin nests may persuade the sparrows to nest in these instead.