Elisabeth Lyons - From the very first moments of life, hatchling loggerhead sea turtles have an arduous task. They must embark on a transoceanic migration, swimming from the Florida coast eastward to the North Atlantic and then gradually migrating over the course of several years before returning again to North American shores. Now, researchers reporting online on February 24 in Current Biology, a Cell Press publication, have figured out how the young turtles find their way.
"One of the great mysteries of animal behavior is how migratory animals can navigate in the open ocean, where there are no visual landmarks," said Kenneth Lohmann of the University of North Carolina at Chapel Hill.
"The most difficult part of open-sea navigation is determining longitude or east-west position. It took human navigators centuries to figure out how to determine longitude on their long-distance voyages," added Nathan Putman, a graduate student in Lohmann's lab and lead author of the study. "This study shows, for the first time, how an animal does this."
It appears that the turtles pick up on magnetic signatures that vary across the Earth's surface in order to determine their position in space—both east-west and north-south—and steer themselves in the right direction. Although several species, including sea turtles, were known to rely on magnetic cues as a surrogate for latitude, the findings come as a surprise because those signals had been considered unpromising for determining east-west position.
The loggerheads' secret is that they rely not on a single feature of the magnetic field, but on a combination of two: the angle at which the magnetic field lines intersect the Earth (a parameter known as inclination) and the strength of the magnetic field.
Near the Equator, the field lines are approximately parallel to the Earth's surface, Putman and Lohmann explained. As one travels north from the Equator, the field lines grow progressively steeper until they reach the poles, where they are directed straight down into the Earth. The magnetic field also varies in intensity, being generally strongest near the poles and weakest near the equator. Both parameters appear to vary more reliably from north to south than east to west, which had led many researchers to conclude that the magnetic field is useful only for latitudinal information.
"Although it is true that an animal capable of detecting only inclination or only intensity would have a hard time determining longitude, loggerhead sea turtles detect both magnetic parameters," Putman said. "This means that they can extract more information from the Earth's field than is initially apparent."
What had been overlooked before is that inclination and intensity vary in slightly different directions across the Earth's surface, Putman added. As a result of that difference, particular oceanic regions have distinct magnetic signatures consisting of a unique combination of inclination and intensity. ...
via Migrating sea turtles have magnetic sense for longitude.
This is from 2001, and makes me wonder if mole rats have the same trick as the turtles.
Do you ever wonder why migrating animals such as birds, salmon, and whales, to name a few, never seem to meander off course and get lost? The answer, according to a couple of new studies, may be that those migration routes and navigation skills are hard-wired into the animals' brains. Studies of loggerhead turtles revealed that hatchlings have the ability to sense the direction and strength of Earth's magnetic field, which they use for navigating along the turtles' regular migration route. ... In a second report published in Science, scientists have discovered a collection of nerve cells in the brains of subterranean Zambian mole rats that enable the animal to process magnetic information used in navigation. The mole rats dig tunnels up to 200 meters (220 yards) long and build their nests in the southernmost tip of their burrows. As the direction of the magnetic field changes, so does the location of the moles' nests. As in the loggerhead turtle study, the German and Czech researchers who conducted the mole rat study have not yet determined how the mole rats detect the magnetic fields. - natgeo
Since the earth's magnetic field is changing, is this confusing animal migrations?
The Earth's Magnetic Pole Shifting: Flux Forces Airport Shutdown In Tampa
The planet's northern magnetic pole is drifting slowly but steadily towards Russia -- and it's throwing off planes in Florida. Tampa International Airport was forced to readjust its runways Thursday to account for the movement of the Earth's magnetic fields, information that pilots rely upon to navigate planes. Thanks to the fluctuations in the force, the airport has closed its primary runway until Jan. 13 to change taxiway signs to account for the shift, the Federal Aviation Administration said. The poles are generated by movements within the Earth's inner and outer cores, though the exact process isn't exactly understood. They're also constantly in flux, moving a few degrees every year, but the changes are almost never of such a magnitude that runways require adjusting, said Paul Takemoto, a spokesman for the FAA. The magnetic fields vary from place to place. Adjustments are needed now at airports in Tampa, but they aren't immediately required at all airports across the country. - conrefoc
Earth’s magnetic field linked to changing orbit
Long-term fluctuations in the intensity and inclination of the Earth’s magnetic field could arise from variations in the eccentricity of our planet’s orbit, according to Japanese geophysicists. Toshitsugu Yamazaki and Hirokuni Oda of the Geological Survey of Japan examined the magnetic properties of a sample of marine sediment deposited over a period of 2.25 million years to establish that the Earth’s magnetic field varies over a 100 000-year cycle. Such studies could shed new light on the energy sources that drive the Earth’s dynamo (T Yamazaki and H Oda 2002 Science 295 2435). ... Astronomers know that the eccentricity of the Earth’s orbit varies between 0 and 0.06 every 100 000 years. This causes the Earth to pass slightly closer to the Sun during certain epochs. Yamazaki and Oda believe that this could induce slight changes in the Earth’s iron core that affect the generation of the magnetic field, and therefore the way that sediment is deposited in the ocean.
Based upon the study of lava flows of basalt throughout the world, it has been proposed that the Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 300,000 years. However, the last such event, called the Brunhes–Matuyama reversal, is observed to have occurred some 780,000 years ago. - physicsworld
Earth's Magnetic field reversals
There is no clear theory as to how the geomagnetic reversals might have occurred. Some scientists have produced models for the core of the Earth wherein the magnetic field is only quasi-stable and the poles can spontaneously migrate from one orientation to the other over the course of a few hundred to a few thousand years. Other scientists propose that the geodynamo first turns itself off, either spontaneously or through some external action like a comet impact, and then restarts itself with the magnetic "North" pole pointing either North or South. External events are not likely to be routine causes of magnetic field reversals due to the lack of a correlation between the age of impact craters and the timing of reversals. Regardless of the cause, when the magnetic pole flips from one hemisphere to the other this is known as a reversal ... - wiki