Let’s say I’m lost in the woods, and this time I don’t feel like improving my predicament by building a house, this time I want to find my way out of there. What’s a directionally challenged girl to do? If the findings of Hynek Burda, Sabine Begall, and colleagues are accurate, I might want to find some cows*.
In 2008, Begall et al published a fairly controversial paper where they used images from Google Earth (cows) and field observations (deer) to determine that cattle and deer preferentially align in a north-south direction:
Figure 1. Distribution of body orientations for cows (A), roe deer (B), and red deer (C), with arrows representing the mean alignment vector. The inner circles represent the threshold for statistical significance. Triangles on the outer edge represent mean alignment orientation for different continents.
Naturally, I had two reactions to this paper: “People can publish stuff like this!?” (that’s awesome!) and “Did they control for all the possible factors?” Perusing the comment thread below the Nature news article reporting on the paper, I saw that many others had the same thoughts. Of course, 99% of people who comment on the interwebs do so without doing their research, not even reading the article on which they’re commenting, let alone following up on any links provided in the article. (Also, 90% of statistics are made up.) So while I read the paper with some skepticism, I ended up fairly satisfied that the authors conducted a rigorous study. To their credit, they also responded to comments in that thread, stating not only that most people who took issue with their paper didn’t actually read the paper (oh snap), but also addressing all of the concerns in detail, so kudos to them!
Figure 2. Risk-free cow-tipping. Photo by blue-moose on Flickr.
Note that the authors don’t claim that cows and deer face a particular direction – say, north, or south (so maybe I’m still hosed even if I do find a deer in the woods) – but that they orient along the north-south axis. They didn’t make the distinction because “The resolution of most satellite images in Google Earth did not allow clear and fast distinction between the individuals’ head and rear…”. Let’s just say… I’ve wanted to say that many times, but not in such polite terms. (^_-)
Prevailing wisdom says that cows tend to orient perpendicular to the sun to maximize heat absorption, or orient with the direction of the wind to avoid heat loss, so sun and wind are obvious confounding factors. The authors took care to rule out both of these factors. With sun, they looked for evidence of behavior related to basking or heat stress, and found none. They also ruled out avoidance of “dazzling” since most images were taken near noon, when the sun is more or less directly above the animals. With wind, they note that there being windy conditions with the wind blowing in a north-south direction in most of their sample is highly improbable. Especially given the prevailing winds in each hemisphere, the animals should align themselves east-west rather than north-south. If their samples consisted of mostly windless conditions, and wind was the dominant orienting factor, then they should have observed a random distribution of body orientations, not the significant north-south orientation.
With deer, they found an even stronger association with a north-south orientation (Figure 1 B and C), again ruling out wind and sun as potential factors. Without wind and sun, the authors posit that the earth’s magnetic field may be the cause. They point out other examples of magnetic alignment in animals, including insects and fish as support for this explanation.
“But what about cow magnets?!” cried some. Never fear – the authors also address this in their response to comments, saying that the use of cow magnets (which are inserted into some cattle when they’re young to catch all the barbed wire, nails and staples these hardcore grazers ingest) is not common, especially in most of the areas where the images came from. They also note that none of the deer would be expected to have magnets in their stomachs, and the north-south effect was even greater for them.
Figure 3. Cows and power lines - who's the boss? Photo by chris_hunnicutt on Flickr.
Earlier this week, the same authors published a follow-up study that bolstered their previous findings that ruminants may be aligning themselves relative to magnetic fields. Here, they investigate the orientation of cattle and deer in the proximity of power lines, again using images from Google Earth for cattle and field observations for deer. They demonstrate that the significant north-south tendency they observed previously is severely reduced when power lines enter the picture, with animals adopting essentially random orientations.
When they stratified the data by the orientation of the power lines themselves, they found that animals may tend to orient themselves roughly parallel to them, but most of the observations were not statistically significant. An obvious factor here is the use of the power lines as a visual cue. So the authors plotted the orientation of animals at increasing distances from the power lines and found that for E-W power lines, the animals as a whole progressively oriented themselves more and more N-S, and for N-S power lines, the orientation of the animals went from random to more and more significant along the N-S axis. The opposite would be expected if the animals were using the power lines as a visual cue.
Figure 4. Orientation becomes increasingly north-south with increasing distance from power lines.
If you’re like me, you’re also intrigued by the way they visualized their data. Maybe these circle diagrams are typical in animal alignment studies but this was the first time I’d seen one, and I’m a fan. A lot of information in a small space, intuitive to interpret once told the underlying concept, and no unnecessary embellishments. So bravo on the data viz front! But how did they make these diagrams, you ask? I would never have guessed it, but they apparently used Powerpoint:
“Screenshots of the chosen pastures were copied from Google Earth and pasted into Microsoft Powerpoint. … We marked the cattle’s longitudinal axis by drawing a straight line with the Powerpoint drawing tools and estimated for each animal separately its direction to the nearest 5° by overlaying a circular scale with 10° steps.”
That’s not to say that they didn’t redraw the diagrams in a different drawing program for publication, but yeah. Powerpoint. Granted, I used Keynote to mock up logos so maybe it’s just because these programs offer a blank canvas and simple drawing tools.
So what can we conclude? Perhaps cows and deer do preferentially align themselves north-south when not under the influence. The use of Google Earth, while cool, does take a bit of environmental control out of the hands of the researcher, though. Could there be artifacts introduced by their data source? Next time I’m in the woods and I happen upon a herd of resting or grazing deer, maybe I’ll make an observation and send it to them. Heck, they should set up a “MagneticRuminantZoo” type thing, where people can enter individual observations of grazing and resting ruminants. Let’s settle this with the awesome power of crowdsourcing!
*Actually, I’m pretty sure deer are probably more common in the woods than cows, but cows worked better with the title. Good thing the phenomenon seems to be even stronger in deer than in cows!
Burda H, Begall S, Cerveny J, Neef J, Nemec P. Extremely low-frequency electromagnetic fields disrupt magnetic alignment of ruminants. Proc Natl Acad Sci (Epub ahead of print)
Begall S, Cerveny J, Neef J, Vojtech O, Nemec P. Magnetic alignment in grazing and resting cattle and deer. Proc Natl Acad Sci. 105(36):13451-13455.
Cressey D. ‘Magnetic cows’ are visible from space. Nature News, August 25, 2008.