My experience has been, they're almost impossible to discourage! We had
swallows building nests in our double carport in Virginia. I watched them
bring in mud, etc. from a nearby pond. The first year we allowed it.
Thought it would be educational for our two little girls! It was a learning
experience allright. Our cars were covered with bird poop until the babies
finally fledged.

Joan Macdonald
Issaquah, WA