For the same reason you do. Bluebirds eat to gain energy to complete the basic functions of life.
No, they do not.
Yes, the eat caterpillars.
No, they do not.
No, they do not eat mice. They eat insects, seeds, and berries.
Yes.
Yes if they can.
no
yes
Eastern bluebirds are very nice birds and eat many garden pests.
Yes, but only small spiders.
They eat common garden insect pests.
No, the also eat small insects such as worms or ticks.