When birds aren't at your feeder it sometimes is because there are very fresh and plentiful natural foods in their neighborhood that they are preferring. As far as your feeder they like black oil sunflower seeds, striped sunflower seeds, safflower seeds and more. They could be busy feeding fledglings which require lots of bugs. Here is information about the parental care at the fledgling stage from our Birds of the World subscription site.

<>Association with Parents or Other Young From Kinser (67), and others as noted: For first 11 days after fledging, young rarely move from branches on which they are perched; in one Indiana study, each fledgling was fed a mean of 8 times/hr (range 4–15, n = 60 hours of observation), with feedings usually in a series of trips in rapid succession. From about 12 to 20 days after fledging, young move around more, occasionally leaving parental territory, but still receiving almost all food from parents. After this, young continue to be fed at least occasionally until 25–56 days after fledging; last young of season receive food over longer period than earlier broods (315, 293). When just 1 young fledges, both parents feed it initially, but after ~12 days, female generally stops to start new nest (67). Prior to female's re-nesting, fledged brood may be divided among parents (280, 208); afterward, male feeds all young until next brood hatches (100), and occasionally for a couple of days longer (314). In southern Ontario, across breeding season, young are fed for average 32 d after fledging (n = 13 clutches; 293); in southern Indiana, for average 39.2 d after hatching (n = 16 clutches). Young may permanently leave parental territory by themselves, or they may be driven

https://birdsoftheworld.org/bow/species/norcar/cur/breeding#young   Here is a list of natural foods they could be eating instead:  

Vegetation: Northeast. Primary vegetable foods include fruits and seeds of grape (Vitis), smartweed (Polygonum), dogwood (Cornus), sedge (Carex), mulberry (Morus), sumac (Rhus), vervain (Verbena), tulip-tree (Liriodendron tulipifera), and domestic corn (Zea mays) and oats (Avena sativa). Southeast. Includes bristle grass (Setaria), blackberry (Rubus), grape, sedge, panic grass (Panicum), and corn. Southern prairies. Includes grape, doveweed (Croton), bristle grass, dogwood, mulberry, knotweed (Polygonum), and hackberry (Celtis). Southwest. In Sonora, Mexico, fruits of Bursera (including B. hindsiana, B. microphylla, and B. laxiflora) are consumed and may be important during periods of drought (197). Animal Food From McAtee (217). Larval and adult insects, including beetles (Coleoptera), mantises (Mantodea) photo , grasshoppers (Acrididae), crickets (Gryllidae), katydids (Tettigoniidae; eggs), butterflies and moths (Lepidoptera), cicadas (Cicadidae), leafhoppers (Cicadellidae) and other small homopterans (Homoptera), stinkbugs (Pentatomidae) and other true bugs (Hemiptera), ants (Formicidae), sawflies (Symphyta), dragonflies (Anisoptera), mayflies (Ephemeroptera), lacewings (Neuroptera), and flies (Diptera). Also, spiders (Araneae), centipedes (Chilopoda), snails and occasional slugs (Gastropoda), and bivalves (Bivalvia). Known to consume periodical cicada (Magicicada spp., 224). from Birds of the World.