Yellow-bellied willow warbler (scientific name: Phylloscopus affinis): 88–106 mm in length, yellow-bellied willow warbler male and female plumage similar. No central or side crests. The upper body is olive green or olive gray-green , the wings and tail are brown or dark brown , the outer feather margin is greenish yellow , the central tail feather shaft is white , there are no wing spots on the wing , and the feather margins are also yellow-green or yellowish-white. The eyebrow lines are yellow, long and broad, from the nose to the side of the pillow, and the eye lines are pale black. The underparts are yellow or yellowish-green , the thorax , neck sides and flanks are olive in color , the undertail coverts are dark grass yellow , and the underwing coverts and axillary feathers are yellow. The iris is dark brown; the upper mouth is dark brown, the lower mouth is light yellow, and the tip is dark brown; the tarsal and toes are pale yellowish brown, or light greenish brown to black.
Distribution in China Xinjiang (Ili, Hami), Shaanxi (Dingbian, Taibai), Inner Mongolia (Helan Mountain), Gansu (Northwest Heaven temple, southern Wushan, western Lanzhou, Sunan), Tibet (southern Lhasa, Dangxiongyang Bajing, Shigatse, eastern-southern region, northern and southwestern Qamdo region), Guizhou (Longli, Leishan), Qinghai (northeastern, eastern, eastern Dulan of Qaidam Basin, southeastern Maqin, Jimai, Zeku), Sichuan (northern Songpan, Nanping, northwestern Shiqu, Dege, western Kangding to Batang, Emei in the center, Chengdu), Yunnan (the western Yingjiang River and the northwestern Lijiang Mountains are breeding birds, and the rest are winter migratory birds).
The habitat is diverse, from forest areas and farming areas above 2000 meters above sea level to highland shrubland areas above 4500 meters above sea level. Its natural habitats are medium and alpine forests at an altitude of 1000-5000 m and in alpine or highland shrublands above the upper forest limit. It is found in broad-leaved forests at an altitude of 1100 m in the Qinling Mountains; in Sichuan and Guizhou, it is also found in interforestation, forest edges and alpine shrublands above 1100 m above sea level, especially in the forest edge and river valley shrubland areas; in Tibet, it inhabits farmland from farmland at an altitude of 2000 m to alpine shrublands of nearly 5000 m; and in Qinghai, it mostly inhabits forest edges and grassland shrublands. It is a small bird with a main alpine and shrubland habitat. Yellow-bellied willow warblers are more common birds. It is often carried out alone or in pairs, and in the non-breeding period, it is also seen in small groups of 3-5 animals into more than 10 animals. Very agile, agile, foraging in shrubs close to the ground, sometimes climbing onto branches or leaves for short distances off the ground and into the air to prey on flying insects. Constantly jumping and feeding among the branches, sometimes jumping and running on the ground.
The breeding period is from May to August, mainly from June to July. Nests usually nest in the lower part of a shrubland not high above the ground, and are oval or spherical in shape, consisting of grass, sometimes mixed with a small number of thin branches, cushioned with thick feathers, and the entrance is close to the apex. The outer diameter of the nest is 13-14 cm, the inner diameter is 7.0-7.5 cm, the height is 7-8 cm, and the depth is 6-7 cm cm. The outer layer of the nest is hay and a very small number of thin branches, and the inner layer is lined with highland quail feathers and other bird feathers. Both clutches lay 3-5 eggs, which are ivory-white.