NATU cannot fly because its wings are not yet fully grown. If your eyes meet with this POKéMON's eyes, it will stare back intently at you. But if you move even slightly, it will hop away to safety.
Sapphire:
NATU has a highly developed jumping ability. The POKéMON flaps and leaps onto tree branches that are taller than grown-up people to pick at the tree's new shoots.
Fire Red:
It usually forages for food on the ground but may, on rare occasions, hop onto branches to peck at shoots.
Leaf Green:
Because its wings aren't yet fully grown, it has to hop to get around. It is always staring at something.