American Goldfinches have great balance and can perch on many different stems while twisting their bodies in acrobatic mastery to get to seeds or fruit. Around the Guelph Lake Nature Centre, I have watched the goldfinches feeding on Cup Plant seeds. Some of their other food preferences include: thistles, ragweed, dandelions, mullein, American Elm, grasses, sunflowers, and Evening Primrose. They also eat some insects. The next photo shows feeding signs on Timothy grass. We did not see the bird that ate these seeds but a good guess would be goldfinches. I recommend the following site for identifying types of grasses: Pasture Grasses Identified.