There is a definite pecking order in the bird world. The Mocking Birds rule over most everything here except large woodpeckers, crows, and occasional blue jays. Some days they will just declare the feeder off limits to all birds and sit nearby and run anyone off that comes near it. They will stick with it for hours.
The cardinals and blue jays are pretty non-confrontational and live and let live types but occasionally a cardinal will nip at a sparrow crowding in on him. We named the cardinal couple Doug and Carrie after King of Queens as she spent her first summer here attacking her image in the reflection from our windows, pickup outside mirrors, the black Weber grill, etc. Drove us nuts.
The larger woodpeckers are paranoid as heck and if we even glance in their direction they are gone. The littler ones have more staying power.
We have a couple Carolina wrens that remind me of chipmunks. They are curious and investigate everything, tail licking too and fro.
And then there are the hoards of sparrows and juncos that normally cover the feeder like ants on honey. The are only distinguished by some make of sparrow that has distinct stripes over its head and back and down its chest. I’ve named him Rambo as he doesn’t tolerate anyone getting closer than 6 or 7 inches from him. Closer than that he charges after them with feathers flared and beak snapping. Only if the intruder is about double his size will he give up and leave.
Kind of entertaining in the winter watching all their antics.