This is definitely the worst of the grinding achievements and should definitely be attempted last, as all of the other grinding will contribute to this one. You need to launch a total of 5000 birds. All levels and attempts are counted. The best level for grinding this achievement is 2-40, as this is the only level with 5 birds. First zoom all the way out so the screen panning is not an issue. Just launch all of the birds backwards (to the left), off the screen. Fire the birds as fast as you can. Restart as soon as you launch the fifth bird. You can launch around 30 birds per minute. This achievement will likely take 2 to 3 hours of solid grinding after earning all of the other achievements.