Mine (goldfinches) disappeared too and still aren't at the feeders in the numbers that they were earlier in spring (this is Ohio). They are busy building nests, tending babies and finding other natural food sources. My house finches are still here (maybe the ones you referred to as your "red" finches?).
Do you have nesting sites nearby? They will seek food first near the nest (wouldn't you?)
Mine are scarce in the summer, too. They find other food sources (which are abundant now), and are busy raising families. They'll be back.
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