Google Earth's collection of satellite images covers the globe (and beyond), offering viewers a realistic view of millions of locations. Users can take virtual tours, learn about distant places, and explore the world.

Scientists are putting Google Earth to good use, as well. In 2008, a group of researchers pored through satellite images of cows from Google Earth. The group, led by Sabine Begall of the University of Duisburg-Essen in Germany, found that cows were not positioning themselves willy-nilly in their pastures; they aligned their bodies in a north-south direction.

Begall and colleagues thought the most likely explanation for their finding was magnetic alignment. This is a simple directional response to the earth's geomagnetic field. Some animals prefer to orient their bodies, especially when resting, in a certain direction with respect to the north-south axis. Magnetic alignment has been found in diverse animals, including honeybees, fruit flies, zebrafish, bats, foxes, and some rodents.

More familiar are the animals that use their magnetic sense as a cue in long migrations, such as sea turtles and pigeons. The detection and use of the planet's magnetic field for navigation is a well-accepted and well-studied phenomenon. Simple magnetic alignment is less readily acknowledged. This could be because magnetic alignment is a subtler behavior or because we don't really know why animals do it. And it could be due to the difficulty in observing magnetic alignment in many animals.

That's where Google Earth comes in. Its widely accessible collection of satellite images allowed scientists a bird's-eye view of how cows were aligned with respect to Earth's magnetic field.

Recently, another group of researchers set out to independently assess cow alignment and find other factors that might influence whether cows line up with the Earth's magnetic field. Pavel Slaby and colleagues from Masaryk University in the Czech Republic again used Google Earth satellite photos to analyze the positions of 2,235 cows from 74 herds in Europe and North America. They used the same or even more stringent criteria than the Begall group: they did not count cows that were eating, drinking, or following a visible track, and herds had to be at least 25 meters from settlements, 150 meters from electric power lines, and 15 meters from pasture borders or fences.

After analyzing the positions of individual cows and the mean alignment of whole herds, Slaby and colleagues found their data supported Begall's original conclusion: resting cows in flat pastures do prefer to align their bodies in the north-south direction.

When Slaby and colleagues divided the herds into three groups based on their density, the picture became a little more complicated. Cows in low-density herds aligned with the north-south axis, whether they were evaluated individually or as a herd. But Slaby and colleagues found no such orientation in high-density herds, either in individual cows or herds as a whole. Cows in the middle-density group were intermediate, with magnetic alignment in individual cows but not in herds averaged together.

Photo: Velvetwire Photo by patries71, distributed under a CC BY-NC-ND 2.0 license.

Why would higher-density herds not show magnetic alignment? Slaby and colleagues say cows' social lives may get in the way. "The attention paid to others depending on whether they are higher or lower in hierarchy, the division of limited room within a group or simply getting out of the way when moving are all competing activities potentially masking the north-south alignment," writes Slaby.

There is still the question of why an animal would choose to align its body with the north-south axis. Unfortunately, the best we can do is speculate.

In ruminants like cows, magnetic alignment may help keep the course of grazing and synchronize the movement of individuals within herds. It may also help herds make efficient, coordinated escapes from predators. Or perhaps maintaining a certain magnetic direction helps cows mentally map their everyday surroundings and learn new landmarks.

Some scientists have proposed interactions between magnetic alignment and some physiological processes. This speculation comes not from studies of animals but experiments involving humans. In people, sleepers aligned in the east-west position show a shortened REM latency compared to those in the north-south position. And scientists have found differences in the EEG scans of normal, healthy people depending on whether they sit facing the north-south or east-west direction.

At present, the biological function of magnetic alignment remains a mystery. We aren't even sure how widespread it is in the animal kingdom. It took looking at cows from space to recognize the phenomenon in one of the most common domesticated animals with which we live. Scientists will have to continue using new technological tools and looking for subtle evidence to get to the bottom of this enigma.

References:

Begall, S., Červený, J., Neef, J., Vojtěch, O., and Burda, H. (2008). Magnetic alignment in grazing and resting cattle and deer. PNAS 105(36): 13451-13455. doi: 10.1073/pnas.0803650105

Begall, S., Malkemper, E. P., Červený, J., Němec, P., and Burda, H. (2013). Magnetic alignment in mammals and other animals. Mammalian Biology - Zeitschrift für Säugetierkunde 78(1): 10–20. http://dx.doi.org/10.1016/j.mambio.2012.05.005

Slaby, P., Tomanova, K., and Vacha, M. (2013). Cattle on pastures do align along the North–South axis, but the alignment depends on herd density. J Comp Physiol A 199(8): 695-701.

doi:10.1007/s00359-013-0827-5