You can also lay your blocks out on a scrap of batting and that works pretty well too. If you stack them, put a piece of tissue or plastic between the layers so the bottom of the last scrap of batting won't grab the quilt pieces on the bottom layer.

We have been advised NOT to use threads or strings for birds nests. They do not dry out as quickly as natural twigs, leaves, etc and the baby birds can get sick from being wet.