How to reach 100% total destruction with the Mighty Eagle in Angry Birds?

I recently purchased the Mighty Eagle in Angry Birds for iPhone. To use him, you toss out a can of sardines and the Eagle swoops down to retrieve it, destroying everything in it's path, including all the pigs. If the Eagle destroys everything, you get a feather (you're rated on a percentage scale, e.g. 85% destroyed, 93% destroyed, etc.). Get enough feathers and you earn some achievements. I've been able to earn a few feathers, but haven't figured out what has to happen to get to 100%. Everytime I've earned 100%, there are usually some wood/glass/stone pieces leftover.

What criteria does the game use to measure the amount of destruction the Mighty Eagle has wreaked?

A simple way would be to keep trying till you destroy everything. Note that you can use some of the other birds before using the Eagle!

However, there is a "4-stars" score for each level, invisible to you. (See: Eagle Score on this AngryBirdsNest post). You have to reach that score with the eagle to get 100%. The percentage of that score you get is the percentage shown to you. Note that just like with regular scores, how the bricks fall affects the points/percentage you get, and not just how much you destroy.

Spoiler: Check out this YouTube video for an example of how to get 100%:

Note that there are some differences between the Mighty Eagle and the Space Eagle:

[U]sing a space eagle doesn’t automatically wipe out all the pigs. Instead, you have to pick the perfect spot to fling the can of sardines, and the space eagle will appear in a wormhole of destruction that pops all the pigs around it.

But don’t worry, space eagles travel in flocks -- so if your first try doesn’t do the job, bring on another space eagle! Unlike the Mighty Eagle, there are no time restrictions on use, and you can use several per level.