How does a bird find a worm in the ground?

Before the sun rises and warms up the earth's surface, earthworms usually crawl up to the earth's surface while it is still cool and damp with the morning dew. That's also the time they fall prey to the "early" (and hungry) birds. When a bird stands on the ground near a worm which is crawiling underneath, the bird can feel the earth's vibrations with its feet. The bird can also hear the worm tunneling in the earth below with their ears.