Q:  What happens to the chicks when the adult birds migrate?  (Vikas, Chennai, India)

A bar-tailed godwit on the Arctic tundra. Godwits' long, slightly scooped bills evolved for fast, deep stabbing into wet mud in search of buried prey, such as clams.  Photo courtesy of the US Fish & Wildlife Service.

A:  When the young are old enough to fly, for hundreds of bird species (for instance, the Canadian goose) the young-of-the-year accompany the adults as they migrate.  But the young of many species, like golden eagles, white-crowned sparrows and swifts, don't.  In fact, most fledglings of shorebirds migrate on their own a few weeks after the adults leave:  an incredible feat. 

“The pronounced age-related differential migrations is common among shorebirds, emails biologist Robert Gill of the USGS Science Center in Anchorage, Alaska.  Take, for example, the bar-tailed godwit, a wading bird that migrates from the subArctic shores of the Bering Sea to the shores of Australia and New Zealand — nonstop 6,800 miles (11 000 km) — and back again, six months later.  Let's follow one chick along a likely route.

It's a cool, moist day in mid September, in the high forties, on Kinak Bay about 20 miles north of where the Kuskokwim  River meets the Bering Sea.  The gray-blue bay stretches out into the misty horizon and vanishes in the clouds.  Throngs of godwits wheel in the sky, and dot the intertidal flats.  Their high-pitched chanting cries* fill the air.  A low-pressure weather system has moved in; strong winds blow south.  A big juvenile, heavy (double her normal weight) with fat stored for the coming ordeal, cocks her head, and tests the winds.  The right direction, she thinks.  Strong, steady.

Sep. 8, 2004, central Yukon River delta. Two juveniles, soon to migrate, fly low over the river. Photo courtesy of Robert Gill, USGS Science Center.

She leaps into the air, joins a group of other juvenile godwits likewise taking off and points her long, slightly scooped bill south, the tailwind pushing her the way she wants to go.  Recently her body has shrunk parts, like the gut, not necessary for flight.  She can't stop on the ocean to feed (she would drown) so she replaced unneeded organ weight with fat and muscle.  Even though chunky with fuel, her body is a streamlined flying machine.  She climbs to flight altitude and settles into a wing-beat rhythm for efficient flight, going about 45 mph (70 km/h). 

A black-tailed godwit chick, ringed in south Iceland, was discovered two years (and four migrations) later only three miles (5 km) from where it hatched. Black-tailed gotwits migrate only a few thousand kilometers nonstop flight, but travel from Iceland to Africa and Australia.  Photo courtesy of Operation Godwit, copyright, used with permission.

The tailwind propels her in the right direction for maybe 600 miles (1000 km).  Eventually the low-pressure north wind dies, but she keeps flying south, somehow, perhaps glancing at the Sun in the day and stars at night for orientation.  Maybe she uses the Earth's magnetic field, too, to keep heading down the vast Pacific Ocean to New Zealand.  But, really, it's a mystery how she successfully navigates for the first time with no experienced guides to show the way.

Finally six days later, burning muscle for fuel (her fat reserves gone), she arrives — totally exhausted, lean and bedraggled.  She drifts down, and lands on a sunny spit in the Bay of Plenty in northwest New Zealand.  Here, in the land down under, it's spring.  Immediately, she thrusts her long bill into the mud, and finds a fat, aquatic worm.  Gobbling fast, she pokes again.  Video.

Map showing the probable flight corridor of migrating bar-tailed gotwits (black dots show distribution of sighting records). Map courtesy of Robert Gill and the USGS Science Center.

With luck, we may know this year if the birds are truly making this lengthy migration nonstop.  We think they do fly nonstop, because we find few banded birds in Asia.  Robert Gill plans to surgically implant tiny transmitter radios inside five female godwits, and then track them via satellite as they migrate.  In fact, the news may be in...  Stay tuned.

*Please note:  loading Adobe Reader's Flash program may change your default video settings.

Further Reading:

Crossing the ultimate ecological barrier:  evidence for an 11 000-km-long nonstop flight from Alaska to New Zealand and eastern Australia by bar-tailed godwits by Robert E. Gill, Jr., Theunis Piersma, Gary Hufford, Rene Servranckx and Adrian Riegen, The Condor

The bar-tailed godwit's nonstop to New Zealand by Ned Rozell, Alaska Science Forum

Ecology of black-tailed gotwits, Snæfellsnes Research Centre

The bar-tailed godwit (and calls), The Royal Society for the Protection of Birds

Kuaka, the bar-tailed godwit, New Zealand Birds

Wings on the wind by David Catchpoole, Answers in Genesis

Firefly encyclopedia of birds, edited by Christopher Perrins

Video of a bar-tailed godwit in Hungary by Boqabirder, YouTube.com

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