Some interesting information gleaned from The Birdwatching Answer Book from The Cornell Lab of Ornithology.
Feeding Nyjer Seed
What looks like seeds on the ground beneath a feeder filled with Nyjer seed are mostly just the emptied-out outer shells. Finches slit open the outer coat and use their tongue to extract the tiny seed inside. Of course, the seeds are so tiny that when a finch pulls out one seed, a few others do spill on the ground. But finches usually arrive at feeders in flocks, and while some birds are sitting at the feeders, others are on the ground picking up the spilled seed.
House Sparrows and Blackbirds
If these species are taking over your seed feeders and you would prefer they don’t, Cornell Lab of Ornithology has this suggestion. Try offering striped sunflower seeds only, rather than seed mixtures or black oil sunflower seeds. Black oil sunflower is a little more nutritious but has a much thinner shell, easier for House sparrows and Black birds to open. Cornell also recommends this so that House sparrows are not being subsidized because they nest in cavities they cannot excavate themselves and therefore take nesting cavities away from other vulnerable native species.