We all know birds migrate by detecting Earth’s magnetic field—but how? This has been a mystery that left ornithologists dumbfounded, but recent findings suggest a convincing explanation. The answer lies within an unassuming pigeon.
A team of biologists, led by Gregory C. Nordmann, employed two separate methodologies to identify the pigeon’s biological “compass,” or magnetoreception, built into their anatomy.
“Birds are capable of going anywhere—over mountains, across the ocean—and this dramatically increases the amount of resources that are available to them,” Dale Fiess, AP Environmental Science teacher, said. “So it makes sense that they would evolve mechanisms to be able to go from one resource to another according to seasons and locations. Many different mechanisms allow birds to migrate, and magnetoreception is just one example.”
There were two primary hypotheses to explain magnetoreception in birds. One was that birds had a quantum-physics effect in retinal cells that allowed them to “see” Earth’s magnetic fields. The other was that certain particles in birds’ beaks acted as tiny compasses. However, the answers to our question lie in the pigeon’s vestibular system.
The vestibular system is a sensory organ in the inner ear that enables vertebrates to detect motion and provide a sense of balance. The basic structure of the vestibular system consists of three perpendicular fluid-filled loops. As liquids move through the loops, they send signals to the brain along three axes: x, y, and z.
By monitoring brain activity using genetic markers, Nordmann’s team found evidence suggesting that the vestibular system was also responsible for providing information about magnetic fields to the pigeon’s brain. The results showed that the pigeon’s vestibular system was sending information to areas of the brain thought to be involved in magnetic field processing.
In other animals, however, it is uncommon for the vestibular system to be connected to brain regions related to magnetoreception. Thus, this did not explain how birds’ neurons could physically sense these magnetic fields.
To answer this question, Nordmann’s team employed their second procedure and performed single-cell RNA sequencing on the pigeons. It turned out that pigeons had an ubiquitous abundance of proteins sensitive to electromagnetic fields. Through this, Nordmann and his colleagues surmised that the vestibular system supplied the pigeon’s brain with the x, y, and z components of the magnetic field.
“Researchers and scientists nowadays have more advanced technology available for them to isolate and manipulate certain factors while controlling others,” Luke Seo (12), former AP Biology student, said. “Technology plays a huge factor in scientific research like this one, so it definitely enabled the researchers to isolate and find evidence for this organ.”
This labyrinthine research, which took Nordmann’s team over 10 years to put together, raises interesting questions about the origins of magnetoreception and migration in Aves.
“It is most likely that these pigeons have inherited a certain response in accordance with their magnetoreception,” Niko Lambert, AP Biology teacher, said. “Many of these behaviors that are inherited are generally in response to some kind of stimulus. For example, certain animals evolve to exhibit a specific behavioral response to the color red. It does not mean that they are seeing red and making an active decision to do something. It is simply hard-coded into their DNA so that when they see red, they respond in a specific way.”
Nordmann’s team has made significant progress in ornithology, but this is only the beginning of avian science.
“Even if birds had acquired magnetic receptors, how does the wiring in their brain tell them where to go?” Mr. Fiess said. “Unlike many other evolutionary capabilities, there is nothing in between the process of learning such a complex evolutionary capability. Migration is definitely one of the more fascinating aspects of evolution, and there are so many more questions to come.”
