September is a big month for the goldfinch. Their numbers should be increasing daily as fledglings emerge from their nests. Your feeders filled with nyjer and sunflower chips will be busy with lots of these little birds jockeying for position. They will also eat coneflower seed heads (sunflowers, thistle, asters) well into the winter months, so leave them standing if you can. Other variety of birds will love that you leave the plants that have gone to seed too. Goldfinches are frequent visitors at the birdbath too, especially those with moving water.
Also, beginning in September, and continuing for six to eight weeks, the goldfinch will molt all of their feathers, ending up with a completely new and pristine set of feathers (and drab colors) as they head into the winter. The young males in their second year get some of the yellow coat of feathers, but will not turn bright yellow until their second summer. Juvenile birds in the fall have the most drab of all goldfinch plumages.