Recent studies show that birds like Robins find worms in the ground visually, not by hearing or smell.
When robins run along the lawn, cocking their heads, it looks like listening, but actually it is just looking.
What the robin usually sees is the castings or pellets of mud at the entrance to the worm hole.
However, worm detection methods vary from one species to another. Shorebirds like sandpipers have sensitive tips to their bills so they can feel worms that they may not see.
And kiwis actually have nostrils at the tip of the bill and a very good sense of smell, allowing them to find earthworms and other food.