The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

5. It's Taken Centuries, but We Now Know Why Deer Don't Ask to Use Your Compass

t h e t h r e e - m i n u t e o u t d o o r s m a n 28 5 it’s taken centuries, but we now know why deer don’t ask to use your compass Natural history is about learning basic facts about plants and animals, where they occur, what they do, how they interact, and so on. Many scientific journals are devoted to reporting observations that scientists make about natural history. The public, however, sometimes does not fully understand what “natural history ” entails—as the editor of one prominent journal reported after receiving a letter requesting a list of nude beaches in a Latin America country. At one time I would have wagered that we have missed relatively few “obvious” things that occur in nature. We know about migration, hibernation, what habitat birds use, who eats whom, who’s the fastest, and so on. But not all things can be observed with the unaided eye, and some things that animals do require sophisticated technology for us to see or understand them. For example, in the past twenty years we have learned that many birds have a well-developed ability to see in the ultraviolet (UV) part of the light spectrum. And scientific experiments have now well established that birds communicate visually with patches of UV plumage, which we simply cannot see. We miss much of what birds are telling each other because we are blind to the signals. Still, you would think that something basic, something that can be observed with the unaided eye, would not have escaped centuries of observations. Right? Apparently we have missed something. It was reported by Sabine Begall (from Essen, Germany ) and colleagues Jaroslav Ćervený, Julia Neef, Oldřich Vojtěch, and Hynek Burda in one of the most prestigious scientific journals, the Proceedings of the National Academy of Sciences. But before I give it away, here’s some background. A L L T H I N G S D E E R 29 Ranchers have known for a long time that most sheep and cattle in a group face the same way when grazing. Farmers know that cattle usually face into the wind, whereas sheep face away from it. When it is cold and the sun is out, you’ll probably see grazing animals orient perpendicular to the sun to absorb the most solar radiation. On a cold, windy winter’s day, you’ll most likely see cows (and hence the whole herd) orient themselves into a strong wind, exposing the least amount of body surface area. These behaviors occur in stressful conditions. But what happens when conditions are not particularly stressful? One would think that the direction of body orientation would be random. Yet we now know that cows and two kinds of deer in Europe (red and roe) orient themselves very strongly in a north–south direction in nonstressful conditions! No way, how could we have missed this? How Begall and her colleagues figured this out is pretty cool to say the least. Believe it or not, they said they looked at maps on Google Earth and that they could see cows in pastures and determine which direction they were facing. I was skeptical, so I asked Begall to send me coordinates so I could see for myself—they weren’t kidding! Try it yourself by visiting Google Earth and entering 36º58′57.57″ S, 61º42′11.55″ W. Sure enough you can see a herd of cows in an Argentine pasture oriented north–south, from space! They actually used images like this to figure out which way the cattle were standing. Begall and colleagues reasoned that because their images were from Africa, Asia, Australia, Europe, North and South America, and Australia, it was unlikely that the wind and sun were the same in all places and that these could not explain the consistent north–south body orientation. They concluded that cattle were using the earth’s magnetic field. We do know that lots of animals, like birds, use magnetic lines of force to navigate. Now we know that cattle and deer also can sense magnetic lines of force and use them to orient themselves. But wait, you say, what about deer? Well, they have field t h e t h r e e - m i n u t e o u t d o o r s...