Why is the gizzard comparatively more muscular than the protriventriculus?

The gizzard is comparatively more muscular than the protriventriculus because it plays a crucial role in mechanically grinding food, aiding digestion in birds that lack teeth. Its strong muscular walls facilitate the breakdown of hard seeds and grains, allowing for more efficient nutrient absorption. In contrast, the protriventriculus mainly serves as a storage area for food before it passes to the gizzard, requiring less muscular development. This specialization reflects the differing functional demands of these digestive organs.