OK, well, you need to have someone find the nest, and get rid of it; and you will have to make sure there are no other places other than the vent where they can get in, and close those up.
I am here as well; I have merely been keeping a low profile. Wishing you well with your diagnosis @Charlet. Knowing for certain what it is that ails you is the first step toward effective management of it.
Until I played one of the Carmen games from 1995 with Lynn Thigpen, and I found a note left behind from one of her agents, I didn't realize that Carmen pays her people too Lol