Why do pidgeons appear to peck the ground even when there’s no obvious signs of food/crumbs?

Question

Why do pidgeons appear to peck the ground even when there’s no obvious signs of food/crumbs?

In: 6775

Answer 1

Many birds swallow sharp pebbles and grit (*gastroliths*) and hold these rocks in a muscular part of their stomachs called the **gizzard**. The **gizzard** contracts and grinds the *gastroliths* against each other and against the food that the bird has swallowed (remember that birds have to swallow each bite whole). The rocks grind down the food — essentially, the bird is using the *gastroliths* to chew the food in its **gizzard** — and the rocks grind each other down, too. Eventually the sharp, jagged chunks of rock become smooth, rounded pebbles, and they are not much good for grinding anymore. So the bird will vomit them out and find new, sharp rocks to swallow.

https://ucmp.berkeley.edu/taxa/verts/archosaurs/gastroliths.php