Although I thought this to be hard at first and spent alot of time trying to get it playing level 1, I found a sure fire way you'll get it your first try.
Load level 13 (This takes 30,000 points on normal play threw) and about half way threw the level you come to a place that honestly has about 50 birds in the air on screen (up close) at once. Its almost impossible not to get 7 with one shot. If you wait a couple seconds most of the birds fly into each other coming from both sides of the screen and you are able to get alot at once, personal best of 13 with 1 shot. Any questions please feel free to comment so I can edit post if I overlooked something.