"The Darkling Thrush" is the story of a little bitty bird taking on the big, bad world. Sure, times are tough. It's cold and gray and awful out there – as our speaker makes abundantly clear every chance that he gets. But, hey, what does the bird have to lose? He's on his way out, anyway. Might as well sing a little song to pass the time, eh? We get a sense of just how miraculous the bird's perseverance is by comparing him to our less-than-hopeful speaker. The thrush is cheerful enough on his own, but next to our speaker, this little guy is the Miss Congeniality of the century!
By ending "The Darkling Thrush" with the promise of Hope, Hardy allows possibility to emerge out of a long and bitter struggle against darkness.
By concluding "The Darkling Thrush" with a bird's song, Hardy emphasizes the ways that happiness remains out of the scope of human comprehension.