In The Solitary Reaper, the nightingale's song is welcoming because it gives great comfort to weary travelers who rest in shady places 'among Arabian sands.'
The nightingale is a favorite subject in Romantic English poetry. Its popularity stems from the Greek myth of Philomela. Philomela is the sister of Procne, who is married to the licentious King Tereus. Tereus takes a liking to Philomela and eventually rapes her. To hide his culpability, he has Philomela's tongue cut out. Not content with this, he also hides her away.
Philomela eventually manages to smuggle out a tapestry depicting her fate at the hands of Tereus to Procne. Both sisters avenge themselves on Tereus by killing Itys (Tereus' son) and cooking him up in a stew for the king. When King Tereus realizes what has happened, he goes into a rage and attacks the sisters. Zeus intervenes and turns everyone into birds. Philomela becomes a nightingale. In nature, the female nightingale does not sing; it is the male which sings the most beautiful songs. It is fitting that even though Philomela is now mute, she will still be able to voice 'old, unhappy far-off things' and 'Some natural sorrow, loss, or pain' through the songs of the male. Tereus' ploy to shut Philomela up for good has failed.
Even though English poetry always imbues the nightingale with a female persona, the message is still clear: the song of the nightingale will always be a great comfort to every weary traveler who has ever experienced private trials and sorrows in the journey of life.