Found this interesting article on bird migration on the New York Time web page.

Adele Freeland
Federal Way
maamfree at gte.net


> This article from NYTimes.com
> \----------------------------------------------------------/
>
> A Low-Tech Compass for Arctic Shorebirds: Just Use the Sun
>
> January 16, 2001
>
> By HENRY FOUNTAIN
>
> As any long-haul airline pilot knows, the shortest distance between
> two points on earth is not along a constant compass heading, but
> rather along what in spherical geometry is called a great circle.
> So to conserve fuel and save time, a pilot usually flies a great
> circle route, relying on a compass or some higher technology like
> radio beacons or satellites to make the frequent directional
> changes required.
>
> Researchers in Sweden and Iceland have now discovered that certain
> Arctic shorebirds accomplish this navigational feat as well, flying
> what amount to great circle routes on their annual summer
> migrations across the Canadian Arctic on their way to South
> America. But there is nothing high-tech about it, the researchers
> say, as the birds apparently rely only on a solar compass, using
> the position of the sun and their innate sense of time to guide
> them.
>
> Thomas Alerstam, a professor of animal ecology at Lund University
> in Sweden, and the other researchers tracked migrating flocks of
> plovers and sandpipers across the Arctic, using radar aboard an
> icebreaker traveling the Northwest Passage. Using the altitude,
> direction and speed data obtained, the researchers were able to
> extrapolate the birds' migratory paths. Their conclusions are
> reported in the current issue of the journal Science.
>
> Studies of pigeons and songbirds have shown that they use some
> combination of internal compasses for navigation ? orienting
> themselves in relation to the sun, the stars or the earth's
> magnetic field, often with the aid of geographical cues from the
> ground.
>
> While pigeons are known to use sun compasses on homing flights,
> and some birds that migrate at night take directional cues from
> polarized light at twilight, there has been little evidence that
> daytime migrators make direct use of the sun. "It's been assumed
> that when looking at migration, star compasses and magnetic
> compasses are more important," Dr. Alerstam said.
>
> He and his colleagues set out to determine whether, in fact,
> Arctic shorebirds could be using a sun compass. They did it in
> classic fashion ? by ruling out use of the other kinds of
> compasses.
>
> By studying the birds as they traveled during the Arctic summer,
> when there is nearly constant daylight, navigation by the stars
> could be eliminated. The birds' proximity to the magnetic North
> Pole, where the magnetic field is extremely distorted, meant that
> any internal magnetic compass would be useless ? a bird relying on
> it would wind up, literally, in Siberia. And because much of the
> birds' journey was across featureless tundra, pack ice or open
> water, they would get little navigational help from the landscape.
>
> "In this area, with its special difficulties, birds seem to be
> able to use the sun in long-distance migration," Dr. Alerstam said.
> "That's a really new thing."
>
> Dr. Kenneth P. Able, a professor at the State University of New
> York at Albany, who has studied bird navigation for decades, said
> that little had been known about how shorebirds navigated, largely
> because they are difficult to work with in a laboratory and because
> they migrate across inaccessible areas. "We don't even really know
> for a fact that shorebirds even have a star compass," Dr. Able
> said.
>
> Given where the birds studied by Dr. Alerstam are flying, Dr. Able
> added, "it certainly makes some sense that these birds would be
> using the sun compass."
>
> Dr. Robert C. Beason, a bird researcher who is chairman of the
> biology department at the University of Louisiana at Monroe, said
> that birds were generally thought to use multiple orientation cues,
> with the ability to reject one or other types of cue if needed.
> "They are pretty much opportunistic," Dr. Beason said. "If the
> magnetic information is unreliable, there's good evidence they
> don't use it."
>
> A great circle is defined as a line traced on the surface of a
> globe by a plane that passes through the globe's center. (Any line
> of longitude, for example, is a great circle, but all lines of
> latitude except the equator are not.)
>
> But just orienting themselves by the position of the sun would not
> cause the Arctic birds to fly along a great circle. It is the use
> of such a compass, in combination with the birds' own jet-lagged
> internal clock, that results in this kind of route.
>
> Crossing the Arctic, the birds pass through many degrees of
> longitude in a relatively short distance (far shorter, say, than
> when crossing the United States). So their internal clocks quickly
> become out of phase with local time, and this, Dr. Alerstam said,
> introduces errors in their use of the sun compass that result in an
> approximation of a great circle route.
>
> As an example, Dr. Alerstam said, consider a bird traveling east
> across the Arctic. On the first day at noon, the sun will be due
> south, and the bird can head due east by orienting itself 90
> degrees to the left of the sun's position. The next day, however,
> when the jet-lagged bird thinks it is noon, it is actually later by
> local time. So the sun will be somewhere west of due south, and a
> bird that orients itself in the same way will be heading
> south-southeast.
>
> That, in fact, is what the tracking data show the birds to be
> doing as they head toward known stopover points in eastern Canada
> before traveling to their winter quarters in South America. "It's a
> nice solution to a very complicated calculation in spherical
> geometry," Dr. Alerstam said.
>
> It is also a fortunate solution, in that the errors result in a
> route that is the shortest and requires the least expenditure of
> energy. "The birds are doing the right thing if they are following
> a great circle," Dr. Alerstam said.
>
> And that raises the question of whether they are just lucky, or if
> they have, in essence, made themselves lucky through adaptation.
>
> "It certainly is not unreasonable to think that this is an
> evolved, adaptive response to the fact that the other mechanisms
> don't work very well," Dr. Able said.
>
> "By chance, the sun compass does work very well under this
> circumstance," he added. "Those that try to use something else are
> going to end up in a bad place."
>
>
> http://www.nytimes.com/2001/01/16/science/16BIRD.html?ex=982431616&ei=1&en=ffc249c6176a0a01
>