Golden swiftlets are also called white swallows, official swallows, and yellow swallows

The tarsometatarsus is completely naked or almost completely exposed, and the shafts of the tail feathers are not exposed. There are roughly 15 types. They are generally light and agile birds, smaller than barn swallows and lighter in constitution. Male and female are similar. The beak is thin and curved downward; the wing tips are long; the legs are short and thin, with all four toes facing forward, not suitable for walking and holding branches, and can only help to grasp the vertical surface of rocks. The feather color is brown to black on the upper body with a golden sheen, and gray or pure white on the lower body.

The picture comes from Baidu Pictures, and the entry comes from Baidu Encyclopedia