You plant enough of them that the birds can have their fill and you can still harvest some. You can place fine mesh netting around the ripening flower heads to prevent the birds from eating them all.
It is just like birds eating the cherries off trees and the deer eating our vegetable gardens, it is their natural food, so they will eat it. If you want to stop them from eating them, then the best option is to build a net over the flowers. The netting is cheap enough and a few long sticks and some string is all you need. However, you didn't say what kind of cockatoos you are suffering from, the Sulphur Crested Cockatoo is an extremely destructive bird, so you should buy some strong material for those type of birds if you have that, other than that it should be fine.
there really is no way to do that unless you cover the sunflowers or cover the seeds
Put up a scarecrow... or a statue of an owl.
Several varieties of birds love sunflower seeds. Bluejays, cardinals, sparrows and finches love sunflower seeds.
You might consider netting your tomato plants to prevent the birds from eating them.
There are many animals that eat sunflowers and their seeds. Caterpillars do feed on the actual sunflower, while deer enjoy the leaves from the plant. Humans, squirrels, many types of birds, and rabbits eat the sunflower seeds.
wrap the mangoes in plastic bags
I put a lot of seeds out in my backyard for birds; whenever the fat red squirrel is eating the seeds there isn't a bird in sight, except if the bluejay comes in.
Population, squirrels living in an Eco system with birds then the squirrels and birds would make a community.
Birds and their eggs, and rodents, like squirrels. Birds and their eggs, squirrels.
Squirrels, cats, dogs, cold. To prevent those: buy a squirrel baffle (a tool that hangs on a birdhouse and is slippery so they fall off) get an indoor cat hang the bird feeder where your dog cannot get to it and feed the birds all year so they stay during the winter.
hawks and birds
Yes. In fact, this is often selectively bred for, to stop birds from eating the seeds.
Make a wire and mesh fence to keep them out of your garden.
Many types of birds such as woodpeckers nest in trees, squirrels LOVE oak trees (for their acorns) and there are tree lizards also.
A cat might but squirrels are a bit too large for the average house cat to eat. Cats will eat mice and small birds (but only if they learned to eat them, killing them is instinctive but eating them as food must be learned).