A World on the Wing: The Global Odyssey of Migratory Birds

by Scott Weidensaul

It now appears that birds may visualize the earth’s magnetic field through a form of quantum entanglement, which is just as bizarre as it sounds. Quantum mechanics dictates that two particles, created at the same instant, are linked at the most profound level—that they are, in essence, one thing, and remain “entangled” with each other so that regardless of distance, what affects one instantly affects the other. No wonder the technical term in physics for this effect is “spooky action.” Even Einstein was unsettled by the implications.

Microsecond by microsecond, this palette of varying chemical signals, spread across countless entangled pairs of electrons, apparently builds a map in the bird’s eye of the geomagnetic fields through which it is traveling.

Researchers have found that in advance of their flights, migrant birds can bulk up with new muscle mass without really exercising,

They also put on so much fat (in many cases more than doubling their weight in a few weeks) that they are, by any measure, grossly obese, and their blood chemistry at such times resembles that of diabetics and coronary patients—except that they suffer no harm. Nor do birds flying nonstop for days suffer from the effects of sleep deprivation; they can shut down one hemisphere of the brain (along with that side’s eye) for a second or two at a time, switching back and forth as they fly through the night; during the day, they take thousands of little micronaps lasting just a few seconds.

It’s a helluva road trip, since the routes taken by some shearwaters exceed 46,000 miles a year.

Fragmentation, it turns out, brings a host of evils. They include so-called edge predators that thrive in disturbed habitats, creatures like raccoons, skunks, opossums, grackles, crows, jays, and rat snakes—all adept nest predators that are rare or absent from deep woods. Fragments also invite brown-headed cowbirds, grassland birds that parasitize the nests of other songbirds (and which were originally restricted to the Great Plains). What’s more, fragmentation dries out the very forest itself, reducing insect abundance and creating other environmental challenges for the nesting birds.

We may finally be looking at migratory birds the way they should be viewed—not as residents of any one place, but of the whole. These are creatures whose entire life cycles must be understood if we’re to have a prayer of preserving them against the onslaught they face at every moment, and at every step, of their migratory journey.

Red knots, as Theunis Piersma and his colleagues discovered years ago, use a sixth sense unique (so far as is known) among any animals to locate clams far below the surface. The knot’s rapidly probing bill sets up compression waves in the water between sand grains, which “echo” off the hard shell of a mollusk and are detected by a network of densely packed sensory organs in the tip of the beak.

many godwits make a 7,200-mile nonstop flight each autumn from western Alaska to New Zealand, a journey that takes them eight or nine days of uninterrupted flight—the longest nonstop migration known, exercising at the same metabolic rate as a human running endless four-minute miles.

Chickadees, whose lives depend on their ability to store and later retrieve food during the winter, experience a 30 percent increase in the size of the hippocampus, that part of the brain that processes spatial information and memory, in autumn.