I put in peanuts, and wild bird seed.
The black birds, and the squirels only eat the peanuts.
The smaller bids eat the seeds.
I have only seen the Squirrels chase away the black birds, but there are days when it's the other way around.
The smaller birds wait until the peanuts are mostly gone, and they go in.
Since I put in my bird feeder, I have noticed more birds of all species some using my property. I have had a small bird (I think a finch) set up nest on my front porch 3 times. The nests are a few yards from the feeder, and bath.
I have noticed small birds eating spiders under my eaves.
Since man has built houses, and paved land; I can't see how a bird feeder does much of anything besides bring in a lot of species. Peanuts will bring in rats too. Squirels bury the peanuts, and rats will dig them up. Squirels seem to forget where they buried their stash?
I probally over feed with the peanuts. I've noticed the black birds will squawk for peanuts around 4 pm., and the Squirels practically tell me to feed them. There was one who used to rattle tge screen door.
I've noticed this year in particular, the watering platform is used by more birds, and insects. I could be me. I might be thinking they are thirsty because of the drought, but I just see a lot of action in that water. (If you supply water, try to change it daily. There's some bacteria going around.)