by Andy Boyd

Click here for audio of Episode 3167

Today, finding the way home. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Although some people are directionally challenged, it's pretty easy to find our way home from anywhere in the U.S. these days. Not only do we have maps, but GPS devices that talk to us. All well and good. But how is it that some animals are so good at finding their way home? How do they do it?

We needn't look far for examples. Birds travel the same migratory routes year in and year out. One of the most fascinating migratory stories is that of Monarch butterflies. Not only do they travel thousands of miles - a remarkable feat for something as light as a butterfly - but they travel to very specific locations. At their wintering site in the mountains of central Mexico, two hundred and fifty million Monarchs will gather in an area roughly the size of just five football fields. And their migration from that site to and from the eastern U.S. takes roughly four generations. The butterflies that return are four generations removed from those that started the sojourn. And we're left to ask, how did the returning butterflies know where to go?

Cape Cod Cormorant   Photo Credit: John Lienhard

Backyard Monarch Butterfly   Photo Credit: John Lienhard

Homing pigeons pose an equally interesting quandary. Give a homing pigeon good food and a comfortable dwelling place and you can't get rid of it. Drive it to some previously unvisited location, set it free, and it may well get home before you do.

Homing Pidgeon   Photo Credit: Wikimedia

Some fish find their way home, too. The most well known are salmon who are born in freshwater streams, live their lives at sea, then return to the same stream for spawning, having traveled thousands of miles from their birthplace in the interim.

Salmon Jumping   Photo Credit: Flickr

So how do these creatures know where to go? We know bits and pieces. Once salmon reach the correct river mouth, they navigate to the proper tributary by smell, drawing on years-old memories from the trip downstream. How they find their way from the ocean to the correct river is still an open question. It's been proposed that homing pigeons are guided by ultralow frequency sounds, sounds well below the hearing range of humans. Even if so, how that translates to navigational skills we don't know.

Many researchers believe that some animals can sense variations in the earth's magnetic field. If so, we should be able to find the part or parts of the animal's brain and body that serve to detect the field. So far we haven't had much luck, though one theory suggests it may be explainable using a strange aspect of quantum theory known as quantum entanglement. That would indeed be big news, since it's a radical departure from how we study and understand biology.

The reality is that after decades of research we're still not sure how animals perform their seemingly impossible navigational feats. It does seem, however, that they see, hear, feel or smell something we humans can't; that they're privy to a world we can't picture. As one leading researcher reminds us, "it's a mistake to think that we [humans] live in the same sensory world as other animals."

Common Tern   Photo Credit: John Lienhard

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

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The total land area covered by Monarch butterflies in central Mexico varies from year to year as recorded here: I attempted to pick a value that was representative of recent history. Estimates of the number of actual butterflies varies as well, as recorded here: Accessed March 6, 2018.

Richard Gray. Monarch Butterflies Use Internal Compass to Find Their Way. From The Telegraph website: Accessed March 6, 2018.

Laura Helmuth. How Do Birds Find Their Way Home? Birds Must Be Geniuses Because They Use Quantum Mechanics to Navigate. From the Smithsonian Magazine website: Accessed March 6, 2018.

Jane J. Lee. New Theory on How Homing Pigeons Find Home: The Birds Could Be Using the Specific Sound Signatures of Home to Navigate. From the National Geographic website: Accessed March 6, 2018.

Magnetoreception. From the Wikipedia website: Accessed March 6, 2018.

Megan McPhee. How Do Spawning Salmon Navigate Back to the Very Same Stream Where They Were Born? From the Scientific American website: Accessed March 6, 2018.

Migration via Quantum Mechanics. From the Physics Central website: Accessed March 6, 2018.

Richard Nelson. The Longest Migration: Yukon River King Salmon. From the Medium website: Accessed March 6, 2018.

Lisa Pollack. The Nest of Wires We Call the Imagination: A History of Some Key Scientists Behind the Bird Compass Sense. From the website of the NIH Center for Macromolecular Modeling & Bioinformatics at the University of Illinois at Urbana-Champaign, Theoretical and Computational Biophysics Group: Accessed March 6, 2018.