Zugunruhe and Other Sixth Senses

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Godwit
Tony Whitehead

Summer’s on the wane, and yet it’s hard to put a finger on how we know, exactly. Like a moon one night past the full, there’s a sliver missing, a little nibbling at the edges of the season.

Even as the apples hang heavy and the air sharpens on the smell of wild grapes, summer’s riot is pared away. Is it a rattle in the oak leaves, frayed and leathery, when the wind blows? Or a dryness in the roadside flowers, the thirsty look of the goldenrod, the calico asters? Or a new nameless taste in the September air, as if our senses were privy to some intelligence they would just as soon keep to themselves?

The Annual Migration

If you live within sight of a patch of mud, either riverbank or tidal flat or county fairground after the tents have been folded up, you may have noticed a few odd visitors in past weeks. Shorebirds—the sandpipers, the plovers, the dowitchers, the godwits, long- and short-legged, long- and short-billed, gray and brown and white—are among the earliest migrants going south for the winter, stopping for a muddy meal along the way. Long before ice and snow threaten to lock them in, they have left their breeding grounds, many from as far north as the Arctic Circle, and are in route to impossibly distant climes, often in the Southern Hemisphere, reminding us, too, of a new season in the offing.


Bar-tailed Godwit—Photo by Tony Whitehead

The longest unbroken annual migration is that of the bar-tailed godwit, a large shorebird that leaves its breeding grounds in Alaska and flies for eight straight days to its “wintering” (or second summering) grounds in New Zealand, a trip of some 7,000 miles without a single pit-stop along the way. In preparation for such a grueling journey out over the open Pacific, the godwit stores up an enormous amount of fuel in the form of fat, while many of its internal organs not used for flight, such as the liver and the intestines, atrophy almost to the point of disappearing altogether.


Migration Route of the Bar-tailed Godwit—Map courtesy of Te Ara, The Encyclopedia of New Zealand

How Birds Know to Migrate

As with many birds, the changing angle of sunlight, lower and lower in the sky, triggers these changes and cues the preparation for migration.

In order to navigate between such far-flung places, godwits, like most long-distance migrants, rely on more than one set of clues. There is evidence that on clear nights they use stars to orient themselves, by day, the sun—and are able to use them even as these markers shift position in the sky. There are further indications that birds sense the Earth’s magnetic field and are able to correct their course accordingly, as humans would use a compass. Even more amazingly, they seem to recognize variations in that magnetic field and their particular position within it, as though they possessed not only a compass but a map as well, a kind of topographical or GPS overview of the entire landscape. How this is accomplished is not known, perhaps by some as yet undescribed chemical process inside the avian eye.


Purple Sandpiper—Photo by Len Medlock

Bird Sense

Even when these shorebirds finally flutter down to land on their home beach, they rely on powers of perception that border on the magical. Probing here and there for worms or mollusks, the beak of the red knot causes a tiny pressure wave in the sand or mud. Where that wave meets an object—a motionless clamshell, for instance—it is disturbed. And the bird’s beak itself, like a bat echolocating in the dark, is actually sensitive to such minute variations in the pressure wave. In other words, shorebirds are not simply stabbing at random in search of a meal, but like precision instruments, are actually testing the mud or sand. As Tim Birkhead writes in his continually astonishing book Bird Sense, “Rapid and repeated probing, so typical of these wading birds, is thought to allow them to build up a composite three-dimensional image of food items hidden in the sand.”


Red Knot—Photo by Len Medlock

Restlessness

Many species of birds experience a restlessness, called Zugunruhe, in the weeks before their departure. They seem hyperactive, antsy, particularly in the evenings or during the night, moving around or breaking into song for no reason at all. Their sleep patterns are changing. They know they are on the cusp of something new, a change of scene, an adventure. For this year’s fledglings, what that adventure will be is inconceivable. But nonetheless they feel it coming and ready themselves.


American Avocet—Photo by Len Medlock

Sensing the Seasons

Even without magnets in our heads or barometric gauges in our noses, even without wings on our backs and 7,000 miles to cover, we feel the gears of the seasons click forward, slowly, so slowly—at least perceptible, if not always interpretable. Like the dowser (“dowitcher”) who cuts a branch of apple wood to search for underground springs, we use any means at our disposal, not just eyes and ears. A restlessness in the night; a sun just a smidge lower at high noon; a sudden urge to stack wood and lay in a store of canned tomatoes—each a clue, not quite rising to consciousness. Where oh where is the mainspring of that clock, vast, elaborate, of which we are ourselves the dial?

~ By  Henry Walters

About This Blog

Field Notes From the Woods, written by Henry Walters, shares observations and ruminations on plants, wildlife, weather, and other facets of nature. Henry Walters is a naturalist, a teacher, and a falconer. He lives and writes in a cabin in southern New Hampshire on a 1,700-acre tract of conservation land, of which he acts as steward. His poems, essays, and translations have appeared or are forthcoming in a number of print publications, including The Old Farmer’s Almanac.

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Hummingbirds migration

Such a great article. I always feel a bit sad once my hummingbirds leave in the autumn. But, I hope they’re off to happier times, and good food down south! Cheers!

Is the building of wind

Is the building of wind turbines affecting the birds?? My barn swallows this year seem to be in confusion. Many have just "dropped dead" in the hay loft---Leaving in small groups throughout Sept. Late babies, just unusual behaviors from the steady habits of years past---comment??

If birds that usually migrate

If birds that usually migrate decide to stick around, should we be feeding them? Wouldn't that interfere with nature? Lots of birds sites say a little seed won't change their habits, but I would think the perfect microclimate would matter.

Birds' migratory instinct is

Henry Walters's picture

Birds' migratory instinct is incredibly strong. In the case of most of our migrants, the urge to travel to a winter range is irresistable, even if a good food source in the summer range is available. Your hummingbirds will disappear south, no matter how long you put out nectar. Your yellow-bellied sapsuckers will not stick around for a refill of suet. A good rule of thumb for feeding birds is to be consistent: if you are feeding birds through the winter, try to keep feeding all the way until spring (or at least until the bears wake up). The food you are providing is not "unnatural," but be conscious that you are, in a very deep sense, making yourself a part of Nature, and with that privilege comes responsibility! 

Is it true that lots of birds

Is it true that lots of birds who used to migrate don't anymore? Like the robin?

Robins, like most of our

Henry Walters's picture

Robins, like most of our North American migrant species, continue to migrate as they have for generations, although the timing of that migration and the range over which it takes place are never set in stone. Some birds delay their migration for local weather patterns, and many species are responding to longer-term climate change. Robins tend to gather in flocks for the winter, roaming in search of berries and other food sources. For many years they have been extending their winter range northward--if you live in a state in the northern U.S., overwintering robins may be a novelty, many months before the time of the proverbial "first robin of the spring." 

That's over 36 miles per hour

That's over 36 miles per hour without stopping! I didn't think birds could fly that fast especially without stopping for 8 days. Is that really possible?

Given the right winds, flight

Henry Walters's picture

Given the right winds, flight speed is incredible. Even the lumbering Canada Goose, the portly denizen of yards and golf courses, can reach 70 miles per hour or more on migration. And avian fat, strangely enough, is one of the world's most powerful fuel sources, gram for gram. The godwit's nonstop migration is exceptional, but by no means the only journey that requires such unbelievable reserves of energy.

One of the loveliest and most

One of the loveliest and most informative essays on the natural world that I've ever read. Thank you so much, Henry.

wonderfully interesting and

wonderfully interesting and informative article about bird migration.

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