To bury one's bird-like head.

ostrich, common name for a large flightless bird (Struthio camelus) of Africa and parts of SW Asia, allied to the rhea, the emu and the extinct moa. It is the largest of living birds; some males reach a height of 8 ft (244 cm) and weigh from 200 to 300 lb (90–135 kg). The ostrich runs at great speed with wings outspread. The inner of the two toes on each foot is much the larger and bears most of the bird's weight. The ostrich kicks when angered and can inflict serious injury. In both sexes the head, neck, and thighs are bare or scantily feathered. The male is glossy black with beautiful long white plumes on the wings and tail. The female is a dull grayish brown. Usually the polygamous male has from two to six females in his flock. The cock scoops out a hollow for the eggs, which weigh nearly 3 lb (1.35 kg) each. One of the females incubates the eggs during the day, and the cock takes over at night. During the 19th-century vogue for ostrich plumes, farms were established in South Africa and later in North America, Australia, and Europe; after World War I fashions changed and the industry collapsed. Ostriches are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Struthioniformes, family Struthionidae.

hich lay 15–60 eggs in a communal nest scraped in the ground. The male sits at night; the females take turns by day. One-month-old chicks can run with adults, at 40 mph (65 km/hr). To escape detection, an ostrich may lie on the ground with its neck outstretched, a habit that may have given rise to the notion that ostriches bury their heads in the sand.

hides head, thinking itself concealed. [Animal Symbolism: Brewer Dictionary, 788]

Except, they don't. It's a fallacy.