Biyiniao

In Chinese mythology, biyiniao (variously translated as linked-wing birds, shared-wings birds, and likewing birds ), also known as manman, are birds with one eye and one wing each, that must attach to one another and fly in pairs. According to the ancient dictionary Erya, its proper name is jianjian.

Descriptions
From the ancient text Classic of Mountains and Seas (trans. Anne Birrell):

"...There is a bird here which looks like a duck but it only has one wing and one eye. It can only fly if it and another bird join together. Its name is the southwild [manman]. Whenever it appears, there will be severe floods over all under the sky."

"...The country of Likewingbird lies to its east. These birds are green and scarlet. The birds fly in twos, wings to wings. One author says that this country lies east of Mount South."

Cultural significance
Biyiniao appeared in Han and Goguryeo tomb art, and has evolved into a popular cultural symbol of steadfast affection. The famous poem "Changhenge" or "Song of Everlasting Regret" by Bai Juyi (772–846), which retells the love story between Emperor Xuanzong of Tang and his consort Yang Yuhuan, invoked this metaphor, as did poetry by Cao Zhi (192–232) and Chen Weisong (1626–1682). For example, the last four lines of a Cao Zhi poem read: