While humans can't eat rocks, there are some animals, including birds, that eat rocks for their survival. Here's why birds eat rocks:
Birds often eat tiny stones with uneven, blunt edges to aid the process of digestion.
Unlike many other mammals, birds don't have teeth to chew. Instead, they have a gizzard, which is the hind part of the stomach.
Birds swallow stones to help grind the food in the gizzard and help the digestion process.
Commonly ground-dwelling or flightless birds like ostriches, chicken, turkey, and penguins swallow rocks regularly.
According to research, between one-fifth and one-half of stomach contents in ostriches are these rocks or gastroliths, accounting for about one per cent of the total body mass.
There are also some swimming and flying birds like ducks, parrots and crows who are known to swallow small stones to aid their digestion.