In today’s post, I’d like to talk about something that many animals can do, and that humans simply cannot. I’m not referring to flying, breathing through gills, spinning webs, or running at 70 miles an hour across the African Savanna. I don’t even mean echolocation or pheromone detection or electroreception or polarized light detection, although some of these may be topics for future posts.
No, today I’d like to focus on magnetoreception, or the ability to sense the Earth’s magnetic fields as a means of perceiving one’s direction or location.
Many animals are able to sense magnetic fields, including honeybees, fruit flies, sea turtles, newts, lobsters, salmon, sharks and even bacteria, but some of the more in-depth and interesting research has been centered around migratory birds’ ability to use the Earth’s magnetic fields as a navigational aid as they make their long journeys.
While there are many aspects of this phenomenon that are still a mystery to us, scientists currently believe that there are two primary biophysical pathways that may explain how birds are able to navigate using the Earth’s geomagnetic fields. These two pathways are currently believed to coexist and complement each other, even though they involve very different processes.1
The first pathway involves the use of iron-based receptors (crystals of a mineral known as magnetite) in the upper beak that can receive and transmit signals of a magnetic field directly to the bird’s brain via a specific nerve (the trigeminal nerve); the second pathway involves the activation of proteins called cryptochromes in the bird’s retina that, after being exposed to blue light, are sensitive to magnetic fields, enabling retinal cells to convert magnetic signals into visual ones and to transmit these signals to a specific sensory processing region (known as Cluster N) within the area of the bird’s forebrain responsible for vision.2
This second pathway may actually enable the bird to create images based on the magnetism fields – in other words, to actually see the Earth’s magnetism and use it as a navigational aid during migration, even during the dark of night.
Aside from being this being pretty cool, what is one to make of this from the standpoint of comparative cognition? Do we chalk one up for the birds (and the honeybees, fruit flies, sea turtles, etc.) and concede that humans are rather lacking in an important cognitive area?
I can already hear the objections. How can you compare this to those characteristics that truly set humans apart from the rest of animals? This is simply a heightened sensory ability, kind of like good eyesight or a fine sense of smell, and not that significant from the standpoint of higher cognition.
This is a fair point and an understandable (if anthropocentric) way to look at it, but there are still a couple of things you may want to consider:
First, we shouldn’t be overly dismissive of the amount cognitive sophistication involved in the long distance navigational feats. Think about it: migratory birds are able to travel, day and night, in all kinds of weather conditions, over great distances – sometimes thousands of miles – with a level of precision beyond our reach until the advent of GPS systems (thank you, Garmin). This sort of navigation is no simple process, either, as sensory input from multiple sources must be assessed, weighted, properly prioritized, reconciled and synthesized, all on a dynamic basis and in an environment when cues are constantly changing.
Also, consider whether this is another area where we humans may be tempted to slant the playing field to our advantage. While it’s easy to imagine our downplaying the significance of magnetoreception from a cognitive standpoint (after all, I just did), remember that we have no trouble in justifying to ourselves why “non-cognitive” human features, such as opposable thumbs and bipedalism, ought to be considered as important factors in distinguishing our capabilities from those of other animals. The point is not to argue that opposable thumbs weren’t critical to our becoming highly sophisticated tool-makers and users (I assume they were), but rather to suggest that we should be as flexible in thinking about factors pertinent to animal cognitive abilities as we are to those pertinent to our own.
Anyhow, time to fly away for the evening – see you soon!
1University of Oldenburg, Department of Biology and Environmental Sciences, Animal Navigation website, visited July 21, 2011.
2See, e.g., Heyers, D., Zapka, M., Hoffmeister, M., Wild, J., & Mouritsen, H. (2010). Magnetic field changes activate the trigeminal brainstem complex in a migratory bird Proceedings of the National Academy of Sciences, 107 (20), 9394-9399 DOI: 10.1073/pnas.0907068107, and Heyers, D., Manns, M., Luksch, H., Güntürkün, O., & Mouritsen, H. (2007). A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds PLoS ONE, 2 (9) DOI: 10.1371/journal.pone.0000937.