Birds are observant, smart and hungry. Especially during drought conditions and times when food is hard to find, birds of many species hone in on the tender, nutritious, sprouted seedlings in gardens. Some of the culprits are jays, crows, thrashers, sparrows and blackbirds. The only sure-fire prevention for bird damage of young plants is a physical barrier that keeps birds away from the plants. Other methods aren’t reliable. They may work for a while, but then they fail.
Get some canes and put some empty plastic bottles over the top.
Place then around your brasica patch and stretch the netting over the top and peg into the ground or place bricks on the edge of the netting.
Make sure the canes are tall enough to keep the birds from landing on top of the netting and nibbling through it.
Try and keep the netting as taught as you can or the birds could get caught in it.
Depending on the type of netting you have I think it's easier if you have somebody who can give you a hand.
You can get ball shaped fittings that you can slot the ends of the canes into to make a frame work for the netting.