Many people use chicken wire over their seed areas. You also have the option of using row covers or tulle. This depends on how much you want to spend. tulle can be purchased rather cheap at a fabric store like Jo-Anne Fabrics.

Good luck!

if you can find (free throw away) - old window screens. They are already mounted on a light frame, still let the sun and rain through, and you only need them until the seeds germinate, then after you lift them - the plants will get full sun

I've heard that plastic toy snakes can scare away the birds.

I've read about this in the comments of this blog that I frequently read.

Here is a link that might be useful: Garden lost to birds from RedWormComposting