I personally wouldn't risk it. Styrofoam builds up static electricity really easily and gets 'stuck' to things - I've heard it can get stuck in a bird's throat and make them choke.
Try foodgrade paper. I have rolls or sprays of it on my toys like this one... George and Edmund are starring on this website if you scan down to the cockatiels on the table top perch.
My vet says a good rule of thumb is "any man-made plaything you wouldn't give to a baby human, don't give to a bird." I'd say that rules styrofoam out. Glad you ditched it. Good idea, Rebecca, about the food grade paper!
You can put them in parchment type rolls like a loo roll they can unravel or twist it round and round so it sticks out like leaves. If you get can get big enough it can be used to cage linings but amazing toys things.
Just be careful anyone using it for females in case they start making a nest from it :-/
Don't tell me....my leather diary was on the receiving end of The Wrath of Alfie today when I shooed him away from the training treat bowl (he's just recently figured out that it's much less work to just go straight to the treats without the need to perform for them...and gets to the bowl before I do at least once every training session...who's the smart one here we wonder... )