Question

Why does william wordsworth compare the song of solitary reaper to that of nightingale and kuku bird

Answer 1

William Wordsworth was a poet who worshipped nature and the simple country life. In the 'Solitary Reaper' he tries to convey the impression made on him by the pathetic song of a lonely reaper in the Scottish Highlands.It is one of the most beautiful of his lyrics. The music of the poem and the pictures painted linger in our hearts long after we have read the poem. 
The poet was passing by a farm where he witnessed a girl singing a melancholy strain. He could move from there. This sight captivated the poet. The song was like magic. It was as beautiful as the cuckoo bird. According to the poet, the song was about battles which had taken place long ago. It was filled with sorrow, loss and pain.  The song seemed to be never ending. Though the poet mounted up the hill that day but the song left behind a strong impression on his mind. He says that he had never heard such a song ever after that day.

Answer 2

She was single in the field reaping and binding the grains in the field and was singing to herself in such a voice that it was attracting the people who were passing by that way. The poet says that the poem was so enchanting that he stopped to listen the song that was passing by the fields slowly. The poet says that the song is more enchanting than that of the Nightingale and the Cuckoo bird that are said to be more enchanting in the world. 
Even though the poet is so much attracted towards the song sung by the reaper he never knew what the women was singing about in the field, he didn't know about the language and the idea that made her to sing the song while she was reaping the grains, is that about the happiness in the life or sorrow in her life or about the world war which took many lives but the song was heard for a longer time even after the poet passed the field.
The poet states that there is no ending for the song as the song was heard by the poet even after the poet reaches his home and he says that the poem is heard for many days and he keeps on mumbling the song heard in the fields but after many days the poet finds that he has stopped mumbling the poem and he has totally forgotten the poem but he remembers the women who sang the song in the farm and was reaping the grains using her sickle.