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Living and Writing in the Natural World

Stranger than We Think

Fueling up for the journey north

I saw another monarch butterfly last week, and it set me thinking about some of the incredible things non-human animals do, and what it shows about the place of humans in the cosmos.

This monarch was probably the second in a chain of four or five generations of these butterflies, a saga that starts in their overwintering home (in Pacific Grove, California; another locus is northern Mexico). Beginning each spring, each generation flies hundreds of miles north, mates, and lays eggs on milkweed plants. The next generation hatches out, fattens up the larval (caterpillar) phase on the milkweeds, pupates into the adults, and resumes the northward flight again. Ditto for another generation or two.

When mid or late summer arrives, the butterflies somehow “know” that it’s time to cease their migration and begin the homeward trek. The last generation barrrels south, 2,500 miles, yet, and before the early frosts they are safely ensconced in the very same mild winter climates where their great-great grandparents began last spring.

Several things are amazing about this migrational epic. How does an insect brain know where to go? It’s not just “north,” it’s “north to this or that particular summer range.” And how is this knowledge passed on for several generations? They’d not reading books or looking at maps or listening to instructions from their parents—how then? How does the fourth generation know that it’s gone far enough north, and it’s time to turn around and high-tail it back to the same over-winter location where its great-great grandparents started out several months ago? Insect brains are not that large or have that many synaptic connections; how is all this packed into them?

Answer: we don’t know. The butterflies appear to use the sun to navigate, and have cryptochrome photo-receptors in their antennae that confer indications of the earth’s magnetic field. Well, fine. But how do they know where to go and how to get back? Over four generations, yet. There are a few theories, but really, we don’t know.

We know a bit more about the relatively simple, one-generation migrations of birds. Many decades of patient studies by very bright, hard-working scientists have established that birds use three (at least) factors to “find their way” in migrations. They use the sun as a guide. And they use the magnetic field of the earth as another guide.

Can you even detect the magnetic field? Me neither. But birds can, and in two ways, yet. First, birds have small pieces of magnetite, a magnetic iron oxide, located in their beaks, or inner ears, or both for some birds. Second, a magnetism-sensitive chemical reaction occurs in the eyes of birds, probably allowing them to perceive the earth’s magnetic field as something like a pattern of bright and dark spots superimposed on their regular visual field, laid down on a north-south axis. Cool, eh?

As an aside, recent research (by Hynek Burda, published in Frontiers in Zoology in mid-2013) suggests that this second magnetic-field-sensing ability is probably what permits flocks of dozens (sometimes hundreds, sometimes thousands) of waterfowl to land on a lake simultaneously without ending up in a chaotic mess of crashes from collisions with adjacent birds. The birds use the pattern of north-south-oriented spots to always land on a north-south axis, so they’re all coming in parallel to each other, on a due-north (or due-south) line. Researchers also suspect that the angle of descent of the birds, as well as the line, is also fixed by this array of spots on their visual field.

Finally, recent research also indicates that birds use infrasound as a migration tool as well. Infrasound? That’s the domain of very low-frequency sounds (less than 20 Hz), inaudible to our human hears but readily perceived by birds. One source of infrasound frequencies is ocean waves, and it is this source (in addition to t he other two) that homing pigeons (at least) use to figure out where they are, and where they need to go from “here” to arrive at their destination.

The intriguing experiment which suggested use of infrasound by birds (conducted by Jon Hagstrum, published in Experimental Biology early in 2013) took place in an area of upstate New York (west of Ithaca) known to homing-pigeon fanciers as “The Birdmuda Triangle,” due to the frequency with which local pigeons get lost in the area. Turns out that the local terrain often blocks out the infrasound from the coastline, depriving the pigeons of one of the aids they are accustomed to using.

So birds are rather better than us humans at navigation of large distances. I can use the sun to figure out directions reasonably well, but I need a compass before I can use the earth’s magnetic field, and a map to boot. Birds have an inbuilt magnetic-field detector, and know what to do with it, without a map or directions. And infrasound is not within my range of detection at all.

It’s not just birds that can detect and use infrasound. Some mammals do, also. Kangaroo rats detect infrasound vibrations generated by the slithering of snakes, and elephants (both African and Asian) as well as rhinos can generate and hear infrasound rumblings from other individuals, which functions to facilitate mate location and group movements over long distances and hilly terrain (which break up infrasound waves less than “our” frequencies of sound.”

At the other end of the sound wave spectrum, ultrasound (greater than 20,000 Hz) is also inaudible to us humans, but highly important for bats, whales, and porpoises (which are merely small whales) in echolocation, used for detecting prey and obstacles.

As the beginning Monarch butterfly tale indicates, even lowly insects can accomplish feats beyond our human abilities. In the visual domain, most insects can see ultraviolet wavelengths of light, invisible to us humans (unless you have a special gadget with you). In the 1950’s scientists discovered that what appear as uniformly-colored flowers to us humans frequently have a startling pattern of “bulls-eyes” and “landing strips” in the uv range visible to insects. These patterns guide the insects to the pollen and nectar of the flower, thus facilitating pollination.

It gets worse. Paper wasps of the genus Polistes (at least) can actually distinguish individual paper wasps by—their facial features! When a photo of a particular paper wasp’s face is linked with a reward, and photos of other wasps don’t confer a benefit, paper wasps can identify the rewarding wasp’s face 74% of the time. And you just thought all wasps look the same.

The point of all this is that our fellow animal creatures on the planet are quite talented, with capabilities un-imagined by us not so long ago. Butterflies, wasps, birds, kangaroo rats, elephants—and without doubt many other creatures—have sensory equipment and perceptual abilities beyond what we humans possess. They do things beyond what we can do. This is not to disparage humans. But it very definitely generates a “message”. We humans aren’t so superior, after all. We do some things (mainly think) very well. Other things—not so well. Not nearly so well as other creatures.

All the planet’s creatures have features which are “wonder-ful,” and blessed are those humans who realize this truth and appreciate it. For them, the world (and all its inhabitants) is a wondrously strange and fascinating place.

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