Apr 27 2012

GPS for Pigeons

Pigeons have an uncanny ability to navigate accurately over long distances. This has been clearly established and exploited for centuries. Yet scientists are still uncertain about the underlying biological basis for this ability. There are four basic mechanisms that pigeons appear to use in returning to their home loft from an unfamiliar location. They use the position of the sun, the magnetic field of the earth, visual cues, and the dispersal of odors in the environment.

Pigeons, therefore, may get a general direction and orientation so that they know which direction to head in. Once they get to familiar territory they then can use visual and olfactory information to zero in on their home. There has been robust research and at times fierce debate about all of these mechanisms. The one that seems to get the most attention in the press is the orientation to the earth’s magnetic field, which is the subject of a new interesting study.

Researchers looking at the brains of pigeons have found 53 neurons that appear to fire in response to the presence, strength, and orientation of an external magnetic field. If true this would point to an important component of the pigeons “gps” system for sensing not only their directional orientation, but perhaps even their general location. The neurons also seemed to have a maximal response to the approximate field strength of the earth’s magnetic field.

This is all very cool, and could add significantly to our growing model of how pigeons and perhaps other birds sense the earth’s magnetic field and use it for direction. But now let’s consider some important caveats.

First, this is a single study. It needs to be independently replicated with more subjects and better controls. At this point we cannot assume the phenomenon is even real. Many initial findings of this sort do not hold up to replication. If it does hold up, then we will also need to learn more about how these neurons are actually working together to create a positional sense, and see how their function correlates to pigeon behavior.

Further, this study is looking at the “neural correlate” of the pigeons magnetic sense. We still need to discover what the sensing organ is – what organ is actually sensing the magnetic field and sending that information to this cluster of neurons? There have been several hypotheses, but none have been proven. Recently one hypothesis, that the sensing organ was a certain group of iron-containing cells in the pigeons beak, was disproved. It turns out the cells in question were macrophages – cells of the immune system. But it is still possible there are other cells in the beak, or there may be a sensing organ in the inner ear or even in the eyes of pigeons. We simply don’t know.

This is a great example of science at work. We have a phenomenon that is well-established – the ability of pigeons to sense and partly navigate according to the earth’s magnetic field. Scientists have been trying to explain this phenomenon in reductionist terms for decades. The pigeon must have some sensing organ that is capable of responding to the magnetic field, and the pigeon brain must respond to this sensory input in a meaningful way that correlates with direction and/or position. Various hypotheses are being explored and sometimes rejected. Different lines of evidence are also being compared to see if they correlate or conflict.

This is all leading to the goal of developing one coherent model of navigation by magnetic field sensing that explains the phenomenon from beginning to end and not only is consistent with but actually explains every aspect of the phenomenon. It taking time as it’s turning out to be a tricky problem to solve, but I have no doubt that scientists will eventually solve this puzzle.

For those of us who deal with fringe science often it’s easy to forget that regular science is happening all the time, without any paranormal or pseudoscientific controversy. No one is complaining about hyper-reductionist pigeon science, or how “Big Homing Pigeon” is distorting the science.  There are no “Western” or “Eastern” approaches to homing pigeons. There’s probably some crank out there claiming that pigeons use their favorite form a magic to navigate, but if so it’s obscure enough to comfortably ignore.

It is helpful to see how real science operates. It is also helpful to see how the press reports such genuine and ongoing scientific controversies. Typically each study is presented with little context as if it is a definitive blow for one side or one theory. In reality, each study is a baby step adding to the overall endeavor, and only has meaning when put into the proper context of all the other research. That takes good science journalism, however, which is often lacking.

This new study is interesting but it needs to be replicated, at the very least. Then we can see how it fits into the bigger picture of pigeon navigation. It is a fascinating scientific question, one that I have followed for years. I will probably have to follow it for many years to come before a consensus solution emerges. Real science takes time.

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