In Hardy's poem the thrush seems to be able to access a hope, in particular, a blessed hope that he, the observer, was unaware.
Thanks to Slate Magazine for the audio of the poem and the text.
I leant upon a coppice gate
When Frost was spectre-gray,
And Winter's dregs made desolate
The weakening eye of day.
The tangled bine-stems scored the sky
Like strings of broken lyres,
And all mankind that haunted nigh
Had sought their household fires.
The land's sharp features seemed to be
The Century's corpse outleant,
His crypt the cloudy canopy,
The wind his death-lament.
The ancient pulse of germ and birth
Was shrunken hard and dry,
And every spirit upon earth
Seemed fervorless as I.
At once a voice arose among
The bleak twigs overhead
In a full-hearted evensong
Of joy illimited;
An aged thrush, frail, gaunt, and small
In blast-beruffled plume,
Had chosen thus to fling his soul
Upon the growing gloom.
So little cause for carolings
Of such ecstatic sound
Was written on terrestrial things
Afar or nigh around,
That I could think there trembled through
His happy good-night air
Some blessed Hope, whereof he knew
And I was unaware.
31 December 1900