Expiring sunflower seed heads provide nourishment for flocks of songbirds, including Blue Jays. A Blue Jay’s diet consists mostly of insects, seeds, nuts, and grains. And they love acorns, too (yet another reason to plant oak trees!).

Blue Jays are year round residents throughout their range however, thousands do migrate along the Atlantic Coast and Great Lakes. Their migration is a bit of a mystery and one thought is perhaps that juveniles are more likely to migrate than the adults. The flock visiting the sunflower field this morning was about twenty or so in number.
Blue Jay range map