- Breeding areas must contain a source of mud (such as a river bank) for incorporation into the nest structure. In drought-prone areas, you can make a Barn Swallow nest cup.
- Barn Swallows will sometimes reuse old nests, but they avoid ones heavily infested with mites or parasites. They will clean out the old feathers and add new mud to the rim.
- Barn Swallows once nested in caves throughout North America, but now build their nests almost exclusively on human-made structures.