Where sunflower fields border woodland is a variable larder for the birds that can tackle the technique needed. Blue and Great tits have no problem suspending from under the flower heads. Ive seen Dunocks and chaffinch trying to hover under one long enough to grab a seed. Goldfinches seem to prefer perching on the top and reaching under to grab a seed on the edge. The heads on the edge of the field are empty and they progressively move further in to the field, usually returning in large groups to the safety of the trees.