Remember those rope that I used to test as fake nests?
If you cannot remember you need to read this article written sometime back.
Go to: http://swiftletfarming.blogspot.com/2013/09/the-rope-dope.html
I was correct that the birds just need something to hang on when they found a suitable place to erect their nest.
There were only two, one like a newly erected while the other completed nest.
Have a look look at the two pictures: