Analysis of A Twilight Song

Why, rapturous bird, though shades of night
Muffle the leaves and swathe the lawn,
Singest thou still with all thy might,
As though 'twere noon, as though 'twere dawn?
Silence darkens on vale and hill,
But thou, unseen, art singing still.

'Tis because, though in dusky bower,
With love delighted still thou art;
Nor hath the deepening twilight power
To lay a curfew on thy heart.
Thou lovest; and, loving, dost prolong
The sense of sunlight with thy song.

Thus may love's rapture haunt me still
When life's full radiance fadeth slow
Along the faltering west, and fill
With melody my afterglow,
And something of Song's morning might
Linger, to make you doubt 'tis night.