Why an ostrich a really big chicken

Unlike chickens, ostriches don't have a crop. Instead, food material passes down the oesophagus directly into the stomach.

Like chickens, they don't have teeth, so they use coarse, nondigestible material inside the stomach to grind up food. Poultry eat tiny stones known as grit, but ostriches have a drive to pick up large pebbles and stones. While it's normal to find some stones in the stomach, birds may obsessively pick up excessive amounts when under stress. They can end up with a large number of stones or other material in the stomach, obstructing anything from moving through.

The stomach of the ostrich is also unusual. Grazing species like sheep, cattle, and goats are foregut fermenters, digesting food in a big stomach chamber (the rumen). Ostriches are hindgut fermenters, using their voluminous colon filled with bacteria to ferment fibrous food. It gives them the ability to digest fibre from a young age; newly-hatched chicks eat their parents' faeces to set up a healthy gut biome so they can ferment their food.

In the wild, the ostrich diet is roughly 60% plant material, 15% fruits or legumes, 5% insects or small-sized animals such as rats and mice, and 20% grains, salts, and stones, for a total of about 1.3kg per day. In NZ, ostriches need pellets, maize, and high-quality pasture grass.

They may also eat sand, sticks, and large amounts of dry hay, which can cause obstructions.