By Allison Vincent
We often use the phrase “hard-wired” to suggest a natural instinct or reflex – an unconditioned response that happens without thinking, that you feel deep in your bones. Migratory birds in that sense are hard-wired to navigate on long journeys – sometimes crossing continents and oceans, which for their size is a feat worthy of recognition in itself! Consider the Swallow-tailed Kite who travels 5,000 miles crossing South America, Central America, and the Gulf of Mexico spending only months in places like CREW just to turn back and do it all over again! Still, how they do it is even more impressive.
Scientists have been fascinated by the phenomenon of migration even before Darwin’s observations on the HMS Beagle and they continue to research compelling migration theories to this day. One leading explanation concentrates on the biological and chemical makeup of some long-distance migrants and their relationship to the earth’s magnetic field through an adaptation with magnetite.
Magnetite is an iron oxide crystal that aligns with magnetic north, kind of like a tiny compass needle, and amazingly it can be found in the cells of some birds. Scientists think the magnetite crystals even serve as receptors, or inclination compasses, that send directional information input to those species predisposed to this genetic variation. Studies conducted found that magnetite can be adversely affected in the birds by demagnetization either naturally or in the lab; therefore it appears that birds can still defer to their “plan b” with their powerful eyesight.
Extensive research conducted on some populations of birds, especially the Bobolink, has produced fascinating results. Through rigorous and ethically-minded scientific testing, researchers found that when temporarily demagnetized, Bobolinks lose their sense of direction. When their magnetic senses were restored they regained their instinctive migration route.
So what happens when it’s not the researchers disturbing migratory birds’ cellular receptors? Laboratory demagnetization mimics natural disturbances in the environment, such as changes of terrestrial magnetism like earthquakes, tsunamis and even solar flares from the sun. With all the natural interruptions observed in the field, researchers continue to look for birds’ evolutionary/emergency “plan b”.
And they seem to have found their answer in the most fascinating place – the cones of the eye; animals who possess cells that include iron oxide crystals may also have the ability to sense magnetic fields through vision. It appears that birds sensitive to magnetic fields have light-sensitive pigments in their eyes, known as cryptochromes, that serve as magnetic sensors distinguishing magnetic fields through color changes.
Imagine that when a cool color, like blue or green, strikes their eyes, electrons in their eyes become energized resulting in something resembling science fiction – north and south become color-coded! When these birds look toward or away from the magnetically charged poles, their field of vision changes color from intensely colorful to lacking in extraneous color.
Many other animals apparently also have iron oxide crystals in their cells: magnetite has been found in the heads of migratory fish, sea turtles and humpback whales. However, of all the wildlife navigators, birds so far are the best studied.
Migration research is a fascinating field of study and leads one to wonder how widespread these genetic-based abilities have developed in other less studied birds. For instance, could our local migratory Swallow-tailed Kites also use this form of navigation? However likely it seems, thus far research has focused on migration monitoring via tracking studies. The future of research is always ripe for possibilities, so stay connected!
Note: Two great CREW trails to observe the next magnetic migration on are the CREW Flint Pen Strand trails and the CREW Bird Rookery Swamp trails. Keep an eye out for the Bobolinks and other migrants like White Pelicans and Sandhill Cranes that have been observed on these CREW trails.
Read more about this subject in a recent article in Nature (there’s even a model drawing for magnetoreception!)
One Reply to “How some birds use magnetism to migrate”
TH for sharing