Whenever I weeded my flower beds or even my flowerpots, I always found a multitude of seedlings of one certain kind. I didn't know what sort of weed it was, but it seemed prolific and very vigorous. It had one or two pairs of leaves atop a long stalk and a pretty good sized root for a young seedling. They were under my azaleas, in the tomato patch, in flower pots on the patio and by the driveway, even among the evergreens. They didn't seem picky about the amount of sunlight or water, and every specimen I pulled up was thriving. I wondered if other people had trouble with these weeds. Were the seeds scattered by the wind? What were they, anyway?
Finally, I pulled one out of a flowerpot that had a recognizable remnant of the seed casing still clinging to the roots and all was revealed. They were sunflower sprouts. The squirrels weren't just eating the seeds from the bird feeders, they were burying them too, and the seeds were germinating.
If you want to grow sunflowers, I can hook you up with some squirrels that are excellent horticulturists.