The robot and the bluebird - David Lucas

There was once a robot with a broken heart, good for nothing but expiring slowly on a scrap heap.
Then one winter's day a migrating bluebird lands on his shoulder, too exhausted to go further.
The robot offers her shelter in the place where his heart used to be, and her warmth and singing and companionship stir up the last glimmer of energy the robot has; he carries her across snowy wastes to the warm south, whereupon his strength dies out finally.
And there he still stands today like an old hollow tree, home every year to singing birds.