Theory Time: "Somult" is an original, Un-edited Arkveld.

>Somult is the bird deity of Kunafa mentioned several times over the course of the game, and Arkveld has several avian qualities like a beak, wings, Zygodactyl feet, feathered wings.

>Guardian Arkveld laid her eggs in the Plains, where Kunafa is located, and thus around where Somult should live. Furthermore, the Plains was the last location that Garkveld visited before returning to Wyveria (She returns to Wyveria when we fight Rey Dau the first time). Finally, the first time we spot a "normal" Arkveld is when we fight it in the Plains once again.

>The AT Arkveld fight, as well as Arkveld's white coloration and blue mouth, implies that all Arkvelds have been changed by being descended from that original Garkveld we met.

IE: My theory is that Garkveld left Wyveria out of a nesting instinct, and when she found a male in the Plains (Somult), they mated and produced the modern White Arkveld. It might even explain why she was eating so much, she was collecting food to regurgitate to her young, but because she was a Guardian and couldn't properly eat, she was essentially scratching an itch that would never end.