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Which Senses Do Robins Use to Find Worms?
Article | Journal Page

An ornithologist named Dr. Frank Heppner wanted to know how robins located earthworms. He set up experiments, knowing he would need to investigate all the robin's senses. Here are the materials he used for his experiments:

Dr. Heppner’s Experiment Kit
  • Pieces of dead earthworm
  • Living earthworms
  • Rotten eggs
  • Decaying meat
  • Rancid butter
  • Mercaptoacetic acid (which smells like a cross between sewer gas, rotten cabbage, a skunk, and a stinkbug)
  • A small drill
  • A tape recorder that's extremely sensitive at low frequencies

How could you test?
Is the robin looking, listening, feeling, smelling — or tasting?

Dr. Heppner's Experiments and Conclusions

Dr. Heppner used very sensitive recording equipment to record the low-frequency sounds made by burrowing earthworms. He found that robins ignored the sounds.

Dr. Heppner concluded that robins don't seem to notice the smell of worms at all. He observed:"Robins nonchalantly ate foods smelling like rotten eggs, decaying meats, rancid butter, and the absolutely worst smell of all bad smells: mercaptoacetic acid."

Dr. Heppner didn't even consider the possibility that robins use taste to find worms. (Robins capture worms before tasting them, and would have to taste a LOT of dirt to pick out worms using their sense of taste!)

Dr. Heppner wondered if robins could feel the vibrations worms make and sense them that way. He drilled worm-like holes in the ground and placed dead worms in them. The robins peeked in the holes, found the dead worms, and ate them readily! Therefore, he concluded that robins do not rely on their sense of touch to hunt worms.

SIGHT (the conclusion!)
Dr. Heppner supected sight was the most important sense robins use to find worms. He drilled holes that looked exactly like worm holes. Robins ignored the holes UNLESS a worm was inside the hole within visual range. Whether that worm was alive and normal, alive but coated with a bad-smelling odor, or dead, the robins found the worms and ate them. He concluded that sight is the key sense robins use to find earthworms.

National Science Education Standards