When I direct seed my sunflowers, using 6" x 6" spacing, I do 6-12 rows at a time. Then I cover them with floating row cover until they are up a few inches. The birds don't bother them after they are past seedling stage.
Ann

I use plain old nylon net. It lets the sun, air and water through, but no birds. Costs around 29 cents a yard at Wal-Mart.

I have bought a black plastic netting from our nearest Grange-Coop in a 7x100 foot length and put this over my hoops covering my sunflower seeds. This has kept 13 chickens and all the other birds off the suns until they are too tall for the netting and then too dense for the chickens to mess with. Absolutely reusable and a really good buy at about 13.00. However, I will say that dealing with this stuff when you are ready to put it away can be a little daunting. Have someone help you roll it up. Hope this helps.
Kat