Pig Dipper 6-16

Pig Dipper 6-16 is the 16th level in Pig Dipper.The objective of level 6-16 is to use the birds to eliminate all the pigs. Get at least 54000 points for 3 stars.

Difficulty
Gravitational field is pull the objects rather powerful, so the fortress can be hard to destroy.

Strategy
Send the first Blue bird under the westernmost structure. Send the next one south, very far south, barely within the gravitational field. This should take out the two remaining structures.