One of the canonical late-summer goldfinch food sources; goldfinch breeding timing in much of North America is synchronized with sunflower seed maturation.
Composite seed heads feed goldfinches and other small seed-eating songbirds through fall and winter when seeds are allowed to dry on the plant.
Cosmos left to set seed is a noted food source for seed-eating songbirds; NC State Extension lists the plant as attracting birds.
NC State: "Goldfinches eat the seeds with relish." Leave the standing seedheads through winter for goldfinch + other songbird forage.
Goldfinches feed heavily on Echinacea seed heads in late summer and fall — the canonical reason to leave seed heads standing.
Missouri Botanical Garden PlantFinder notes local songbird populations — particularly finches — love to feed on the seeds, and recommends saving seed heads to feed birds in winter.