Eat your own bird feed.

Have you tried opening a squirrel fast food restaurant off to the side, and advertising with lil’ squirrel speakers making squirrel calls? When you really get it going you can start squirrel chains and direct them all to a new squirrel city and then you’ll save your bird feed for the birds!

Add poison to it

Depends on what your arrangement for ordering the birds the seeds is. Is your birdfeeder on a pole? Is it hanging off the ceiling of a sunshade perhaps? Maybe it’s suction cupped to the outside of your window? After that, it depends on what’s available in your locale. If you’re in the US, you have various options. Less so in the third world.

In short you’ll need to provide more details if you want a useful answer.