Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable The Homing Instinct How Do Birds Navigate Fall Migrations? Scientists Say They've = Found the Secrets By Amanda Onion Sept. 27, 2004 - Last Sunday Jack Meyer spotted 10 different = warblers, a bald eagle and a couple varieties of hawks as the birds = paused in New York City's Central Park during their epic journeys to = winter feeding grounds.=20 It was a good day for Meyer, a retiree who earns a little money on = the side by guiding birding tours and identifying the traveling birds. = But when it comes to understanding how the birds manage to navigate = their twice-a-year journeys to summer and winter feeding grounds, the = veteran admits he's confounded.=20 "I understand a little about it, but not much," he said.=20 He's not alone. The question of how migrating birds manage to fly = for hundreds, sometimes thousands of miles, often at night, to end up in = the same spot year after year has been nagging biologists, even = physicists, for decades. Do they hone in on landmarks or familiar = smells? Do they orient themselves using the sun or Earth's magnetic = field?=20 Finally, after years of research, it appears scientists have found = the answer: Yes.=20 It turns out that birds are sophisticated navigators who use a mix = of methods to keep their flights on course.=20 Seasoned Navigators=20 Research has shown they use landmarks as they make their way = overland and homing pigeons (which are not migrating birds) even follow = highways and make their turns at marked exits. New work has revealed = that migrating birds also rely on proteins in their eyes that act like = compasses to keep themselves pointed north or south - depending on the = season. And, because magnetic north shifts and can be an unreliable = guide, they check the setting sun each evening to reset their course.=20 "People like myself have been studying this for a very long time," = said Henrik Mouritsen of the University of Oldenburg in Germany. "How = they get their magnetic sense is the last question that was left to be = understood. Now we're pretty close."=20 To understand the birds' tricks, Mouritsen and his colleagues = first tried to confuse some migrants.=20 Mouritsen and Martin Wikelski of Princeton University in New = Jersey and William Cochran of the Illinois Natural History Survey in = Champaign captured songbirds in Illinois and Iowa as they made their = journeys north in the spring. Then they subjected the birds to a false = magnetic field at dusk and released them.=20 Birds that had been exposed to the warped magnetic field took off = in the wrong direction, but by the second night they had managed to = correct themselves and point north once more.=20 This suggested that the birds use the setting sun to correct their = internal compasses. It's a skill the birds need even if scientists don't = grab them and throw off their magnetic compass because Earth's magnetic = field shifts so magnetic north is often inconsistent with geographical = north.=20 "It's such a simple and elegant mechanism that I would say it is = widespread [among migrating birds]," said Wikelski, who published the = results with his colleagues in an April issue of Science.=20 Which Exit for Florida?=20 For birds that have already flown a route before, plenty of = evidence has suggested the travelers keep tabs on landmarks below to = find their way. In the United States, geographical features tend to = funnel the traveling birds into four main routes - the Atlantic, = Mississippi, Central and Pacific flyways.=20 Migrating birds that have made the trip before become familiar = with particular landmarks and smells along the way and use them to keep = them on course. Some don't limit their visual cues to natural features.=20 A research group led by Hans-Peter Lipp of the University of = Zurich in Switzerland recently used Velcro and glue to attach = lightweight GPS logging devices on the backs of homing pigeons. The = loggers provided data on the flight paths of pigeons as the birds winged = for up to 75 miles in journeys home from various points around Rome. After researchers mapped more than 200 flight paths over three = years, it was clear the birds preferred to travel above highways. In = some cases, the roads veered too far off course from the birds' routes. = When this happened, some birds even waited to see an exit on the highway = before making their turn.=20 "It's like the way a pilot of a small airplane may prefer to = follow a road or powerline coincident with the compass rather than = watching only the compass in the cockpit," explained Lipp.=20 Studies may have shown that birds use cues to find their way, but = scientists have had trouble explaining the key mechanism behind their = navigating feat - their internal compass. In the end, it took both = physicists and biologists to figure out how the birds detect Earth's = magnetic field.=20 Physicists were the first to suggest that migrating birds carry a = protein in their eyes that are activated by blue and green light. When = activated by this light (which is available both night and day), = molecules in the proteins enter an active state and become sensitive to = Earth's magnetic field.=20 It was a good theory, but it hadn't been tested in actual birds' = eyes - until now.=20 Special Vision=20 Mouritsen dissected some garden warblers and located the proteins = in the retinas of birds that had just been exposed to the blue green = light and to a magnetic field. He found the proteins had been altered = according to the change in the magnetic field and had sent this = information to the birds' brains. The result is the birds see Earth's = magnetic field superimposed over their normal vision like a pilot = peering through a mounted target system.=20 "Imagine a light spot with concentric darker rings around it that = moves around in the retina depending on where you look," said Mouritsen, = who published the details of his research in Proceedings of the National = Academy of Sciences. "This is what the bird sees - it's a weak pattern = superimposed on what they see in the world."=20 There are still some questions Mouritsen and others still hope to = answer, such as how the special protein sends information to the brain = and whether any other sensing device might be at play. But, at least for = now, they're satisfied to know even a little about how the birds manage = their amazing feat.=20 Meyer, for his part, is more interested in the birds' moods as = they wing their way north or south. He has found that birds heading = north are usually in a hurry to start breeding and don't stay long at = their rest stops. But those heading south for the summer tend to take a = more leisurely pace.=20 This is why he prefers birding in the fall season.=20 "For the birder and birds, it's less hectic," he said. "You're = less likely to miss some birds before they get back on the flyway."=20 -------------------------------------------- Forward by: Wallace Coffey Bristol, TN =20 =================NOTES TO SUBSCRIBER===================== The TN-Bird Net requires you to sign your messages with first and last name, city (town) and state abbreviation. ----------------------------------------------------- ---------------------------------------------------- To post to this mailing list, simply send email to: tn-bird@xxxxxxxxxxxxxx ----------------------------------------------------- To unsubscribe, send email to: tn-bird-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field. * * * * * * * * * * * * * * * * * * * * * * * * * * * * * TN-Bird Net is owned by the Tennessee Ornithological Society Neither the society(TOS) nor its moderator(s) endorse the views or opinions expressed by the members of this discussion group. 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