>>56998885This would be perfect on an evolutionary and lore level.
Kiwis are born orphans, their mother abandons them after laying and the father only takes care of the egg for a while, when the Kiwi is born it is alone and must fend for itself, being a single egg it has a large amount of nutrients so the baby Kiwi is well developed when it hatches, but on a Pokemon level it could explain why it develops a second head, without parents and without siblings the chick feels alone, in addition the Kiwis are nocturnal and live in the thick of the forest to avoid predators, when it becomes a Emu (Doduo) it has a friend to interact with, it is big enough to leave the forest and when it becomes Dodrio and has another head it requires more resources and becomes a predator, a Terror bird.