Time was when I was free as air,
The thistle's downy seed my fare,
My drink the morning dew;
I perch'd at will on every spray,
My form genteel, my plumage gay,
My strains for ever new.
But gaudy plumage, sprightly strain,
And form genteel were all in vain,
And of a transient date;
For, caught and caged, and starved to death,
In dying sighs my little breath
Soon pass’d the wiry grate.
Thanks, gentle swain, for all my woes,
And thanks for this effectual close
And cure of every ill!
More cruelty could none express;
And I, if you had shown me less,
Had been your prisoner still.

William Cowper

http://www.poemhunter.com/poem/on-a-goldfinch-starved-to-death-in-his-cage/