What's the name of this bird? Round and lovely (taken in the Arctic, Norwegian territory)

Young of yellow-bellied pipit. Yellow-bellied harrier (scientific name: Rabdosia rubescens): It is a small songbird of passeriformes, with a body length of about 15 cm. Like a tree pipit, but the upper body is brown and dense, the upper beak is slender and the top is notched; The wing tip is long, and the inner flight feather (third flight feather) is extremely long, almost flush with the wing tip; The tail is slender and the outer tail feather is white. When parked in the wild, it often swings up and down regularly. The legs are slender and the hind toes have long claws, which is suitable for walking on the ground. Mainly inhabit mountains, forest margins, shrubs, grasslands and river valleys. In winter, we like wet and grassy places along streams and rice fields.