It's an optical illusion! Ostriches are the largest living birds, but their heads are pretty small. "If you see them picking at the ground from a distance, it may look like their heads are buried in the ground," says Glinda Cunningham of the American Ostrich Association.
Ostriches don't bury their heads in the sand—they wouldn't be able to breathe! But they do dig holes in the dirt to use as nests for their eggs. Several times a day, a bird puts her head in the hole and turns the eggs. So it really does look like the birds are burying their heads in the sand!