Since robins find worms by sight, they can use the brightest daylight hours for eating and finding food for their babies, and the darkest times for singing. Journey North's Robin expert stayed up all night once in early July when she was living in Michigan. Dr. Heppner considered ALL the senses that a robin might use to find worms. If robins feel vibrations of live, wiggly worms, they wouldn't bother eating still, dead worms. Using VERY sensitive recording equipment, Dr. Heppner taped the low-frequency sounds made by burrowing earthworms, and found that the robins ignored it.
Robins look for earthworm holes that have a worm within visual range.
Whether that worm was alive and normal, alive but coated with a bad-smelling odor, or dead, the robins found and ate them. Perhaps one big reason why robins are more secretive in forests is because of all the secretive dangers they face while hunting on the forest floor. Robins living in towns and cities spend a lot of time out in the open, where they can more clearly observe people and animals from a long distance. Over time, a civilized robin learns that people aren't dangerous unless they're walking straight toward it, and that most dogs are far less dangerous than cats. In the forest, movements and sounds might not be fully visible until it's too late, so robins tend to be much more secretive.