How to take clips from Event Library and put in separate event folder?

(I looked in iMovie Help menu but found no help.)

I recently did a file transfer from my Sanyo HD2000A which was a large accumulation of clips taken since last spring 2010. This was my first upload.

Now I have a lot of clips organized by date by iMovie '11. There are various categories of these clips, and one of them is +"Ducks in my back yard swimming pool."+ Another is a huge number of clips taken over time of three baby sparrows in the nest outside my window. It is a progression of how they are fed by their parents and how they grow and leave.

My plan is to get them into their own folders, filed by time/recency, and then pick and choose from those two folders/categories during the making of a movie which includes them along with other little adventures.

Question: How can I separate all of the duck clips and the sparrow clips so that they are each in their own folder and not spread out in folders organized by days?

=L