You can collect empty nests no problems (?) Well I can't see AFCD prosecuting you for it (if in country parks, CP's)) although theoretically you cannot substract anything from CP's, even if dead.
When you collect a nest, try to locate where it came from (which plant/building) make a note of it, record date of collection, note the place name, a geographical coordinate is good and attach a label to the nest with these infos on it.
There are a lot of references available on WWW. From the reference sections of these papers/books you'll find more references....it's an expodential curve!
Thanks for your comments on the books