Those are just fondant with cutouts. Very easy to do.
What are the cut outs called? Where can you buy them?
The cake is beautiful! How did I missed it?? Thank you for posting!! Now in reference to your question...the following link will give you an idea.
scroll down.... you will see that you need to get butterfly cookie cutters, after cutting the butterfly shape, use on it any of your Wilton tips (for buttercream)
Scroll down and you will see the tips used. See?? After cutting and making the design that you would like set it to dry in a former, so as to give it a sort of flying shape. HTH
Thanks for the link soledad...that helpd a lot.
You can also use tiny aspic cutters, available at cookware stores and Ateco makes them too.