If I'm correct, the record was made using 4 birds. I got 89K using the following strategy (possibly the record strat):
blue bird: Shoot straight at the bottom ice blocks and break it before it hits. You want to have every thing from the left structure down except 2 or 3 wood planks standing against the middle structure.
red bird: Shoot it at the wood planks standing against the middle structure, hopefully breaking all of them.
Yellow bird: Shoot it in the same area, aiming for the capped pig. The middle structure should more or less collapse after that.
blue bird: Shoot it higher than the other birds, aimed at the far structure. Try to make it collapse, popping the last pig while it does.

As i said, I got 89K doing that and I know there's at least 4-5K left in it. It's just a really frustrating strategy that I can't get to work very often. Get ready to restart because the last pig didn't pop at the very end...

Any tips for 3-21? I want to get around 140K and I can't seem to be able to get near my 134K score... I'm probably doing something wrong. What do you guys do?