What is the difference between digestive system of birds and mammals?

The digestive systems of birds and mammals differ primarily in structure and function. Birds possess a unique organ called the gizzard, which grinds food, allowing them to efficiently process seeds and tough materials, as they often lack teeth. In contrast, mammals typically have teeth for mechanical digestion and a more complex stomach structure that varies among species, such as ruminants having a multi-chambered stomach for fermenting plant material. Additionally, birds have a cloaca, a single exit for digestive and reproductive tracts, whereas mammals have separate openings for these functions.