The bluebird feeder has a normal bird feeder platform with plexiglass panels on each side but no food can get under those side panels like you'd find in a regular bird feeder. The panels are tight to the platform and the only way to access the food is through holes found on each end of the feeder.
I've watched adult bluebirds teach their youngsters how to get in by demonstrating the technique. Here is a series of pictures of a young bluebird who got in but then could only focus on how to get out. He didn't even eat any of the tasty meal worms His only concern was figuring out his exit strategy.
I've said it before but I'll say it again, there's nothing more entertaining than watching these quirky, interesting, beautiful, and smart little birds.