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<\/div>Eurasian reed warblers migrate between Europe and Africa<\/p>\n
AGAMI Photo Agency \/ Alamy Stock<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
Many migratory birds use Earth\u2019s magnetic field as a compass, but some can also use information from that field to determine more or less where they are on a mental map.<\/p>\n
Eurasian reed warblers (Acrocephalus scirpaceus<\/em>) appear to calculate their geographical position by drawing data from different distances and angles between magnetic fields and the Earth\u2019s shape. The findings suggest that the birds use magnetic information as a sort of \u201cGPS\u201d that tells them not only where to go, but where they are initially, says Richard Holland<\/a> at Bangor University in the UK.<\/p>\n \u201cWhen we travel, we have a map \u2013 which tells us where we are \u2013 and we have a compass, which tells us which way to go to reach our destination,\u201d he says. \u201cWe don\u2019t think birds have quite this level of accuracy or degree of knowledge of the whole Earth. Even so, they see how magnetic cues change as they move along their normal path \u2013 or even if they\u2019re far displaced from that path.\u201d<\/p>\n <\/p>\n Scientists have known for decades that migratory birds rely on cues from the sun<\/a>, the stars<\/a> and Earth\u2019s magnetic field<\/a> to determine which direction to head towards. But figuring out direction using a compass is markedly different from knowing where in the world they are, and scientists still debate about whether \u2013 and how \u2013 birds figure out their current map position.<\/p>\n Florian Packmor<\/a> at Lower Saxon Wadden Sea National Park Authority in Germany suspected birds could detect detailed aspects of the magnetic field<\/a> to determine their global position. Specifically, he thought they might use magnetic inclination \u2013 the changing angle of Earth\u2019s surface relative to its magnetic lines \u2013 and magnetic declination \u2013 the difference in direction between the geographic and magnetic poles \u2013 to understand more precisely where they are located in the world.<\/p>\n To test that theory, Packmor, Holland and their colleagues captured 21 adult reed warblers on their migration route from Europe to Africa in Illmitz, Austria. There, they placed the birds temporarily in outdoor aviaries, where the researchers used a Helmholtz coil to interfere with magnetic fields. They artificially altered the inclination and declination in a way that corresponded to a position in Neftekamsk, Russia, 2600 kilometres away. \u201cThat\u2019s way out of their direction,\u201d says Packmor.<\/p>\n The team then put the birds in a special cage for studying migratory instincts and asked two independent researchers \u2013 who were unaware of the changes in magnetic field \u2013 to record which way the birds headed. In the modified magnetic field situations, most of the birds showed a clear penchant for flying west-southwest, as though they were trying to return to their migration route from Russia. By contrast, the same birds wanted to fly south-southeast out of Austria when the magnetic field was unmodified.<\/p>\n This suggests that the birds believed that they were no longer in Austria, but in Russia \u2013 based on their magnetic inclination and declination alone, says Packmor.<\/p>\n \u201cOf course, they don\u2019t know it\u2019s Russia, but it\u2019s too far north and east of where they should be,\u201d says Holland. \u201cAnd then at that point, they look at their compass system to work out how to fly south and west.\u201d<\/p>\n However, we still don\u2019t fully understand the neurological mechanisms that enable birds to sense these aspects of Earth\u2019s magnetic field.<\/p>\n \u201cThis is an important step in understanding how magnetic maps of songbirds \u2013 and in particular, reed warblers \u2013 work,\u201d says Nikita Chernetsov<\/a> at the Zoological Institute of the Russian Academy of Sciences in Saint Petersburg, who was not involved in the study.<\/p>\n While the research confirms reed warblers rely on these magnetic fields for positioning, it doesn\u2019t mean that all birds do so, he adds. \u201cNot all birds work the same way.\u201d<\/p>\n The birds were released two to three weeks after the study, at which time they could continue their normal migration, Packmor and Holland say. Indeed, one of the birds they studied was captured a second time a year later, meaning the team\u2019s research did not prevent it from migrating successfully.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n