What food can be used to attract blue birds?

Answer 1

If you mean an actual bluebird such as the eastern bluebird or the western bluebird. These species are insectivorous. Some people will set up feeders with mealworms for them but that won't necessarily attract them as habitat is what counts for them. They Will also eat small fruits so if you plant small fruiting shrubs they may appreciate. Nice open field, meadows, golf course, orchards, soccer fields are places where they prefer to hang out, they will tend to avoid dense forest and heavily populated areas. If you are in a favorable habitat you can also place nesting boxes to attract them, . Of course if you are simply interested in a blue colored bird, blue grosbeaks, indigo/lazuli buntings and blue jays/ Steller's jays will come to feeders, Black sunflower seed is a good place to start and jays love peanuts !
Which species is present really depends on where you are.

Answer 2

Any tipe of wild birds bird seed.