Ostriches mainly feed on seeds, shrubs, grass, fruit and flowers. Occasionally they also eat insects such as locusts. Lacking teeth, they swallow pebbles that act as gastroliths to grind food in the gizzard.

When eating, they will fill their gullet with food, which is in turn passed down their esophagus in the form of a ball called a bolus. The bolus may be as much as 210 ml (7.1 US fl oz). After passing through the neck (there is no crop) the food enters the gizzard and is worked on by the aforementioned pebbles. The gizzard can hold as much as 1,300 g (46 oz), of which up to 45% may be sand and pebbles.

Common ostriches can go without drinking for several days, using metabolic water and moisture in ingested plants, but they enjoy liquid water and frequently take baths where it is available. They can survive losing up to 25% of their body weight through dehydration.

More Info: en.wikipedia.org