The poem A Lament by P.B. Shelley goes like this
O world! O Life! O Time!
On whose last steps I climb,
Trembling at that where I stood before;
When will return the glory of your prime?
No more, —O never more!
Out of the day and night
A joy has taken flight;
Fresh spring, and summer, and winter hoar
Move my faint heart with grief, but with delight
No more — O never more!
When Shelley wrote “A joy has taken flight” was he making allusions to the skylark whom he called a “blithe spirit”? In his ode “To a Skylark” he called the bird as very joyful and a source of joy for him quite a times. So, it is quite obvious to take that line literally, but if we take it as referring to the blithe spirit the whole poem “A Lament” takes a new luster, but the question is: can we take it like that?