Final answer:
Dodo birds ate rocks to aid in digestion, utilizing a gizzard which contained the swallowed stones that helped in grinding food due to the absence of teeth, maintaining high metabolic rates for energy.
Step-by-step explanation:
Dodo birds ingested stones as an adaptation to aid their digestion. They did not have teeth to chew their food properly, so swallowing stones helped to grind down the food in a specialized organ called the gizzard. The lack of teeth is linked to avian adaptations from their dinosaur ancestors, and this feature is common among birds, particularly those that consume a diet mainly consisting of seeds.
The dodo birds, which lived on Mauritius before extinction, also displayed these adaptations. Despite not flying, these birds would still need to process their food efficiently. The stones in their gizzard acted much like a mill, grinding the food and thus compensating for the absence of mastication which occurs in other animals with teeth.
This process of using stones is essential for many birds since they need to keep their metabolic rates high to sustain their energetic needs, especially since many of them are capable of flight and require quick digestion to maintain low body weight. The dodo's inability to fly did not exempt it from the need for efficient digestion to support its large size and dietary requirements.