How to combine shadow shape with environmental lighting and a model. SOLVED

OK, I give up. I have been playing with this all day and I am at the throw the computer out the window stage PLUS my HD died on me today (backed up a few weeks ago and it is just the media drive but still, all the movies,books and music are gone until I by a new 3T drive)!
SO
How in the word do you do this right?
I have a transparent plane with a bird silhouette as a shadow. I have an environmental light and background. I have a spot and I have my model of a caterpillar and a plant. I want to render the background, model, and bird separately. Blur the bird so it looks more like a shadow (the whole reason I started this madness called compositing) and then recombine it into a nice pic. Oh, and it is in cycles.

The bend is a mess because I have been playing all day with it but I hope it is not to far gone to be helpful.
Thanks Douglas
The blend
http://www.pasteall.org/blend/34856

It remains a bit vague what your problem actually is…?



Background > Alpha over blurred bird > Alpha over plant. Is that what you want to achieve?

Perfect! Thanks @IkariShinji.
My problem? No understanding of the compositor would seem to be the basic problem. I was trying to mix with other nodes and had not found THE way.
Seems the caterpillar was eaten. LOL