Do birds feel the magnetic force of land lines when they migrate?

0

About 1,800 miles below the Earth’s surface lies a 1,367-mile-thick layer of liquefied minerals composed largely of iron and nickel called the outer core. It’s liquefied because it’s hot – 8,132 to 9,932 degrees F – it’s lapping in response to the Earth’s rotation on its axis (1,029 mph at the equator).

Due to the beautiful magic of physics, metals flowing through the outer core create electrical currents which (again, due to the Earth’s rotation) create a magnetic field extending from the North Pole to the South Pole.

Well no.

In fact, the magnetic North Pole is currently located approximately 223 miles southwest of the geographic North Pole. I say currently because its exact location has been drifting NNW towards Siberia at about 25-35 miles per year since 1990. (The magnetic South Pole is currently about 10,630 miles southeast of the geographic South Pole.)

The Earth’s magnetic field does not propagate uniformly in the atmosphere but in distinct lines of force. Place a children’s stir bar on a piece of white paper and sprinkle it liberally with tiny iron filings. Tap the paper and watch the filings line up along the lines of force of the magnet. The Earth’s magnetic field works the same way.

Visitors to the Magee Marsh Wildlife Area have recently been able to see dozens of migrating birds, including the black-throated blue warbler.

It’s been known for a few decades that many animals can sense these magnetic lines of force, but a 2021 study published in the prestigious scientific journal Nature provided our first clear insight into how birds might actually “see” these lines for humans. use as guides. during migration.

When a protein found in bird eyes called cryptochrome 4 (CRY4) was isolated from a European robin in a lab experiment, it was found that blue light sensitized it to the earth’s magnetic field. The process, which involves quantum mechanics, changes the shape of the protein. (Google search “Science News Quantum Compass” for a concise summary of how it works.)

It is speculated that the nervous system of migrating birds can, in a yet unknown way, detect the change in CRY4 proteins in their eyes, allowing them to become aware of – and perhaps even visualize – the Earth’s magnetic lines of force. . CRY4 isolated from chickens, a non-migratory bird, is suggested to be much less sensitive to magnetic fields.

We learn that birds can use the Earth’s magnetic field in more ways than just telling north from south. Consider a famous study conducted by Richard Mewaldt in the winter of 1964.

After banding a group of white-crowned sparrows in his garden in California, he shipped half of them to Louisiana and the other half to Maryland. The following winter, birds from both regions found their way back to his backyard, having first flown to their traditional breeding grounds in the Yukon.

A likely explanation for such GPS-like behavior is now thought to be that migrating birds can find their way across the planet’s surface to specific locations because they had memorized the “magnetic signatures” of those areas. when they were young. Here’s an example of how it might work:

Earth’s magnetic lines of force run parallel to the Earth’s surface at the equator, but dip more and more downward as they approach the north and south magnetic poles. The angle at a given location is called its magnetic inclination. A study published earlier this year presented strong evidence that juvenile reed warblers in Europe memorize magnetic tilt in the area where they are reared.

After wintering in sub-Saharan Africa, they use this angle as a stop sign to decide where to end their return migration north. But birds also have other orientation abilities in their migration toolkit. It has long been known that those who migrate during the day can use the position of the sun to determine direction, while nocturnal migrants refer to the stars in the night sky.

Tricky things to do, though, since both methods require some sort of internal biological clock. To fly due north at noon, for example, you could fly with the sun directly behind you, but that plan wouldn’t work at 9 a.m. or 4 p.m. And rather than memorizing particular constellations, nocturnal migrants (like most of our songbirds) pay attention to the rotation of star clusters around the stationary Pole Star as the night progresses.

It turns out that the ability of birds to synchronize their behavior with the time of day involves a complex set of interacting systems located in the SCN region of the brain, the pineal gland and the retina.

There is also evidence that various species use geographical cues, low-frequency sounds like the rumble of ocean tides or the wind at the top of a mountain range, the polarization of light at sunrise and sunset, and even olfactory signals to find their way.

In the final essay in this three-part series on avian migration, we will examine how migration is thought to have evolved and how birds deal with the many dangers they face during migration.

Ken Baker is a retired professor of biology and environmental studies. If you have a natural history topic that you would like Dr. Baker to consider for an upcoming column, please email your idea to fre-newsdesk@gannett.com.

Share.

Comments are closed.