At some point, while I was in graduate school, it became apparent that I was going to study the problem of finding one’s way around. Navigation, orientation, mental maps, sense of direction, knowledge of the landscape, and related ideas must be linked to how people who live off the land survive, and I was studying the foraging ecology of Efe Pygmies in the Ituri Forest. One of the things I realized early on is that it is very easy to find something in the rain forest, as long as one simple thing is true: You already know where it is. Otherwise, you are sunk. Eventually I was to discover that the Efe managed the foraging mode of their lives by continuously maintaining a personal database of where things are, where to go to possibly get something (because it is sometimes there) and where certain things generally are. There is a certain amount of communication among different people at which time data is exchanged, but far far less than most armchair Hunting and Gathering experts (like, most archaeologists) would ever guess. Knowledge is more likely to be shared via shared experience than the exchange of data, though both happen. I was also eventually to learn that Efe do not have an uncanny built in sense of direction. They simply mostly know where they are in the same way Westerners living in cities or suburbs know where you are (or did, before GPS was everywhere): You know where you are because you got there by going to a place you knew the location of. You have an experiential map (which may not be accurate in 2D spacial terms) which you maintain over time, building bits here and there, forgetting bits here and there.
But early in the process of learning about the Efe I made a foray into the literature available in the 1980s of orientation and navigation, and this included the literature on birds. Back then, it was known that birds were pretty good navigators. Homing pigeons were apparently able to find their way home after being transported in a closed box a long distance away (many hundreds of miles in some cases). It is often forgotten or overlooked that not all homing pigeons found their way home, and some took many weeks. In any event, they were surprisingly good at this. Experiments had been done which involved strapping magnets to the heads of homing pigeons to see if you could confuse them. That did in fact confuse them at least to some degree. One researcher tested British school children to see if they could find their way home by driving them blindfolded, in a bus, out into the country and asking them to point their way home. They had a certain amount of success but not impressively so. The same researcher then did the same thing but with big magnets strapped to the children’s heads.
I don’t remember the outcome off that latest experiment, but I do remember that many people thought the researcher was a bit of a cook and ignored his findings generally.
It turns out that the latest research shows that birds use magnetic information form the Earth’s magenetosphere to find their way around, able to detect the orientation of the magnetic flux as well as its strength. Le-Qing Wu and J. David Dickman, in the April 26th Science Express, write:
Many animals rely on the Earth’s magnetic field for spatial orientation and navigation. However, how the brain receives and interprets magnetic field information is unknown. Support for the existence of magnetic receptors in the vertebrate retina, beak, nose, and inner ear has been proposed and immediate gene expression markers have identified several brain regions activated by magnetic stimulation, but the central neural mechanisms underlying magnetoreception remain unknown. Here, we describe neuronal responses in the pigeon’s brainstem that show how single cells encode magnetic field direction, intensity, and polarity—qualities that are necessary to derive an internal model representing directional heading and geosurface location. Our findings demonstrate a neural substrate for a vertebrate magnetic sense.
So this confirms what we have more or less known all along, but also takes it a step futher, providing physical details that will allow us to figure out how this works more exactly. There has been prior research showing “magnetic properties” of selected cells in bird brain stems, but that work, done over 30 years ago, was too crude.
Whenever we consider bird navigation and magnetics the question must be asked: What happens when the Earth’s Magnetic field reverses? In order to answer that question realistically we would have to know more about the nature of those reversals. So far it looks like the would not have been abrupt events coming out of nowhere, but rather, they would have been preceded by a periods of weakening or other changes in the field. But in any event, one could imagine that magnetic events including reversals would have an effect on bird populations. Some might end up navigating to new areas they previously had not gone to, or disruptions of population distribution or density. Birds surely use multiple methods of getting around, but a major disruption of one method could have caused problems that would have had an impact.
The question I have now is this: If population disruptions were severe enough, would this leave a signature in the genetics of modern bird populations, or of phylogenetic reconstructions across species? Can we possibly see ancient disruptions in bird populations caused by magnetic perturbations? If so, is anyone looking for this? If not, why not? Get to work people!
Greg Laden has been watching birds since they were still dinosaurs, but has remained the consummate amateur. This is probably because he needs better binoculars. Based in the Twin Cities, Minnesota, Greg is a biological anthropologist and Africanist, who writes and teaches about Evolution, especially of humans. He also blogs at Scienceblogs.com. Greg's beat is Bird Evolutionary Biology. One could say that knowing the science of birds can make the birds more interesting. But really, knowing about the birds that go with the science is more likely to make the science more interesting. And thus, birding and Neo Darwinian Theory go hand in hand. Darwin was, after all, a pretty serious birder. Greg has seen a bird eat a monkey in the wild.
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