Juncos feed mostly on the ground, eating weed and grass seeds in the wild. In summer these bird feed mainly on insects. Attracting Juncos to your feeders is as easy as scattering some finely cracked corn or millet seed on a tray feeder. A tray feeder keeps the seed off the ground. Seed tossed on the ground gathers moisture causing the seed to spoil. This can be harmful to the birds.