In ancient poetry, swan geese are generally metaphors for messengers who deliver letters between lovers. This meaning first appeared in the Book of Songs, and later generations adopted this meaning.
Although it was the Tang Dynasty when poetry was at its peak, poets still compared most of the images in the Book of Songs.
For example: In the spring river with flowers and moonlight, "the wild geese fly long and the light does not fly, and the fish and dragon dive and leap into the water" has this meaning.
The translation is: The sky is so vast that even the geese that are good at long-distance flying cannot fly out of the boundless moonlight world, and even the fish and dragons that are good at swimming can only set off layers of ripples but cannot swim to your side. How can I meet you?
Here, the swans, fish and dragons are compared with his eagerness to reunite as husband and wife, which further shows the depth of separation and sorrow for his wife.
Extended information:
The swan goose can be used as a metaphor for people, implying the aloof image of the swan goose.
This is the meaning of the sentence in the secular poem "Bu Suanzi": "Who sees lonely people coming and going alone, misty and lonely shadows".
The translation is: The surroundings are so peaceful and quiet. At this moment when everything is dreaming, who else is wandering lonely under the moonlight like myself, like a lonely wild goose flying across the sky.
Swan geese are a migratory bird, moving south in autumn and north in spring. This is very similar to the situation of refugees who are forced to work in the wild, traveling in all directions and having no fixed place to live. The cry of swan geese during their long journey is shrill and sad, which makes people emotional and adds to the sadness. Therefore, it is most appropriate to use it as a starting point.