We have long known that migratory songbirds navigate in different ways. Our founding editor Eldon Greij noted in an earlier column: “Birds have internal compasses that can determine the direction of the sun during the day, the star patterns and the earth’s magnetic field at night.”
New research shows for the first time that birds that deviate from course can use the magnetic field to find their way back to their migration route.
The team from the Universities of Bangor and Keele studied the Eurasian warbler, a species that breeds in large parts of Europe and parts of Asia, as well as in sub-Saharan Africa in winter. Their study was published today in Current Biology.
The researchers found that the warblers can navigate back to that correct route from a “magnetic position” beyond what they experienced on their normal migration route.
Upper map: Eurasian Reed Warbler breeding area (green) in Europe and variation of the geomagnetic signature (total magnetic intensity, magnetic inclination and magnetic declination). The natural direction of migration from the study site (white point) to Africa in autumn is shown as a black arrow. The expected direction of adjustment from the simulated point (black star) is shown as a white arrow. Pie charts: Left: Orientation of birds that experience the natural magnetic field at the examination site in Austria. Right: Orientation of birds that experience the simulated magnetic field of a location in Russia while they are still at the examination location in Austria. Arrows show the respective middle group direction. Black dots show the orientation of the individual birds tested. Image courtesy of the authors
Different parts of the earth have different geomagnetic signature depending on their location. This is a combination of the strength of the earth’s magnetic field, the magnetic inclination or the angle of inclination between magnetic field lines and the horizon and the magnetic declination or the angle between the directions to the geographic and magnetic north poles.
Adult birds, already familiar with their migratory route and general magnetic signatures, were briefly held in captivity before being released back into the wild, and they became a simulation of the Earth’s magnetic signature in one location thousands of miles away exposed to the natural migration corridor of birds. The study area was in Austria and the warblers were placed in a device that simulated the magnetic field of an area in Russia.
The magnetic field has priority
Although the birds physically remain in their location where they were caught and learn all other sensory clues about their location, including the starlight and sights, smells and sounds of their actual location, they nonetheless showed the urge to begin their journey as if they were at Location suggested by the magnetic signal they were experiencing.
Their orientation was to fly in a direction that would lead them “back” to their migration path from the place suggested to them by the magnetic signals they were experiencing.
This shows that the Earth’s magnetic field is the key factor in guiding Reed Warblers when they are off course.
“The overall impetus was to act on the magnetic information they were receiving,” said Richard Holland of the Bangor University School of Natural Sciences.
“Our current work shows that birds can sense that they are outside the limits of the magnetic fields known to them from their year-round movements, and that they can extrapolate their position sufficiently from the signals. This fascinating ability enables birds to navigate their normal migration path. “
The magnetic setup used in Austria to simulate a displacement of birds off course by exposing them to the magnetic field of the Russian location. Photo by Florian Packmor
Lead author Dmitry Kishkinev from the School of Life Sciences at Keele University stated:
“What these birds achieve is ‘true navigation’. In other words, after relocating to a completely unknown location, they can return to a known destination without relying on familiar surroundings, clues emanating from the destination, or information gathered during the outward journey. “
Florian Packmor of Bangor University, a co-author, added, “We have already shown that the reed warblers use the same magnetic cues that they experienced in their natural realm, but this study shows they can extrapolate what understand them through the magnetic The field varies in space far beyond previous experiences. “
The question remains whether the birds have an accurate “map” or are just using a “rule of thumb” to assess the general direction of travel required to get back on track.
The Eurasian warbler was selected for the research, but the results could likely be applied to other migratory songbirds, the researchers say.
Thank you Bangor University for providing this news.
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