After all of the crown moulding was installed, I then took a tube of flexible, paintable caulk and used it to fill in all of the cracks where it was attached to the ceiling and walls. Also, it was used to fill in the joining cut lines..
The birds are back! They’re now trying to get into the other side of the bay window roof, where the crown moulding is fairly rotted… I went ahead and removed all of the crown moulding… And replaced it with some 1×4. This should deter them, until we get around to restoring this area.