classic waka stream

When spring comes round,
the geese return north again;
on the white clouds’ road
they go their distant way—
would that I could send word.

Meaning
When spring comes, the geese return to the north. They go their way along the road of white clouds; if only I could send a message to the one who went down to the land of Koshi.
Commentary
Spring Songs, Book One

Hearing the cries of the returning geese, the poet thinks of someone who went down to the land of Koshi and composed this poem.

Entrusting a letter to geese is based on the tale of Su Wu of the Former Han,
but the story is not stated openly; hearing the cries of the geese, the poet thinks of a friend in the northern lands.
Author
Oshikochi no Mitsune
Source
Kokin Wakashu
Other