houses

House martin Delichon urbicum at nest in the eaves

Swift Apus apus and House martin Delichon urbicum comparison of the two birds in flight

Nesting tower for swifts, martins, & bats diagram showing the slots for bats, curved slits for swifts and nests for martins

Barn swallow Hirundo rustica viewed from above with small insect in its beak

Swift Apus apus sketch in flight