These are feeders that will help deter grackles and starlings at your feeder station.
We often talk about strategic feeding when grackles and starlings appear and we recommend 3 separate feeders:
1. safflower feeder
2. nyjer feeder
3. Caged feeder
These are the cages or caged feeding systems that allow you to continue feeding a mix or straight sunflower, or suet, while prohibiting the grackles and starlings access.
The safflower and the nyjer, they just don't care for so they will naturally leave those alone after some initial exploration of them.