In the wild bluebirds eat a fairly varied diet of insects and fruits, including many varieties of berries like holly, sumac, cedar, dogwood, mulberry and elderberry. Insects are especially important to bluebirds during the nesting season, as the protein in them is necessary for the hatchlings to grow.
Due to their reliance on insects and fruit, bluebirds typically do not eat from a normal birdfeeder containing seeds. This means that if a person wants to try to feed bluebirds, they need to provide them with mealworms, fruit or suet, a specially designed bird feed made from vegetable or animal fat mixed with fruits and seeds. Although they don't typically eat most seeds, bluebirds have been known to eat sunflower seeds, as well as peanuts.
When feeding bluebirds, the mealworms can be live, canned or roasted. Similarly, they can be fed both fresh and dried fruit. Bluebirds are incredibly fond of mealworms, but it is important to note that they can't live on them alone. This is why some experts recommend that a nesting pair of bluebirds should be fed no more than 200 mealworms per day. For people who have bluebirds nesting on their property, it is important note to use insecticides in such a way as not to harm the birds or take away their main food source.