The mood in "To A Mouse" is one not only of sadness for what he has done to destroy the mouse's winter home while he was out ploughing.
He also apologizes that the world of human beings has encroached on her small existence, even in that she wants so little for herself;
I'm truly sorry Man's dominion
Has broken Nature's social union,
he also can empathize with her:
...thy poor, earth-born companion,
As he continues to accept the blame for her present and dire circumstances of a home destroyed in the cold of winter, which might kill her...
Thou saw the fields laid bare an' wast,
An' weary Winter comin fast,
An' cozie here, beneath the blast,
Thou thought to dwell,
Till crash! the cruel coulter past
Out thro' thy cell.
...he may also feel a kinship with her, inferred here, later in the poem.
That wee-bit heap o' leaves an' stibble,
Has cost thee monie a weary nibble!
Now thou's turn'd out, for a' thy trouble,
He believes that he, too, is in a terrible situation which he did not see coming. While he believes that her problems may be temporary, he looks back into his past and believes the consequences of that past may have far-reaching effects on his future, which to him seems very bleak.
Still, thou art blest, compar'd wi' me!
The present only toucheth thee:
But Och! I backward cast my e'e,
On prospects drear!
An' forward, tho' I canna see,
I guess an' fear!
The primary emotions I detect from Burns' is sadness for the trouble he has caused this little mouse, the kinship he feels for their shared troubles, and his lack of hope for his own future.
(Burns is a well-known and well-loved Scottish poet whose work lingers long after his death.
The best laid schemes o' Mice an' Men,
Gang aft agley,
is often quoted, though translated:
"...the best laid schemes [plans] of mice and men / Go often askew [awry].
Though his dialect is often difficult to follow, he demonstrates his capacity to understand and identify with the feelings of others—in this poem, even with the lowly field mouse.