Animal behaviors that still can't be explained

We learn more and more about animals seemingly every day. Science continues to unlock the great mysteries of why these wacky non-humans do what they do with increasing regularity. But that doesn't mean we know everything — there's still a ton about nature's creations that baffle us to this day. We only have theories as to why animals do the following:

Why do cows face north or south when eating?

Aside from "at the table" or "in front of the TV," you probably don't think much about what direction you face when you eat. But cows do — almost universally, a cow will face either north or south come dinnertime. And while we know how they do it, we have not one idea why. 

According to NPR's All Things Considered show, cows can sense Earth's magnetic field and will align their bodies with it to face north or south while eating — sort of like a compass that goes great with A-1 sauce. What's more, the folks who made the discovery — Hynek Burda and her team at Germany's University of Duisburg-Essen — discovered that other animals, specifically deer, do the same thing, and for seemingly no purpose at all. When birds conform to the planet's magnetic field, it's for navigational purposes. But when's the last time you saw a cow migrate anywhere but to the nearest barn? Mammals simply don't move from this place to that the way birds do, rendering this magnetic path seemingly pointless.

However, animals rarely do stuff for no reason — time wasted means time not eating, after all. So they probably have a purpose when facing north/south. It might be, as biologist Richard Holland theorized (and as quoted by NPR) that mammals did, in fact, once routinely migrate a lot, and the north-facing thing is a mere leftover evolutionary feature. But that, like everything else we think about why they do it, is simply a theory.

How can animals predict earthquakes days or weeks in advance?

It's one thing for an animal to sense an earthquake seconds before it happens — we've known they can do that since ancient Greece wasn't ancient. We even know why: according to the US Geological Survey, two types of waves come out of an earthquake: a large S-wave, and a tiny P-wave that typically arrives seconds before the S-wave. Animals, unlike humans, can sense the tiny P-wave, so when they do, they know it's time to run. So if your pet randomly starts panicking and running off for the safety of higher ground, follow them — because you've got about five seconds before everything around you starts shaking like a Polaroid picture. 

What's baffling, however, is that some animals can sense an earthquake days, or even weeks before it actually happens. As the USGS mentions, in 373 BC, a huge earthquake rattled Greece. But the rats, snakes, and even centipedes all got to stepping long before the natural disaster made its presence known to humans. To this day, we have no idea why. Researcher  Joseph Kirschvink theorized in his 2000 paper Earthquake Prediction by Animals: Evolution and Sensory Perception that there may be more warning signs to earthquakes than we currently know of, some of which arrive weeks in advance, and animals are reacting to those. It makes sense, though as of now, we've detected precisely zero new signs. So what exactly makes these animals panic weeks before we do is still completely unknown.

Why do chimpanzees wage war?

Cute as they may be on bicycles, chimpanzees are downright mean. They're so mean, in fact, they've been known to hunt, kill, and even eat their fellow chimps. What's worse, they do it in an organized, group-oriented, methodical manner, or what we call "war." Yep — chimp tribes have been observed waging war against nearby chimp tribes, meaning Planet Of the Apes isn't that unrealistic after all.

As to why they fight this way — as opposed to how basically every other species hunts merely to eat — is currently unknown. There are several theories though, such as the super-dark one proposed by Harvard's Richard Wrangham in his book Demonic Males: Apes and the Origins of Human Violence (as recapped by the BBC). In Wrangham's mind, chimps wage war because they're genetically inclined to violence, much like humans. Since chimps and humans are extremely close relatives, Wrangham theorizes that if one is war-like, the other must be, too.

However, other researchers, like Robert Sussman and Joshua Marshack from St. Louis's Washington University, reject the idea that chimps wage war because it's in their blood. Rather, to them, chimps are war-like because humans have interfered in their lives. Either they're logging and destroying forests, making territory scarce and forcing chimps to be more aggressive, or they're feeding them special foods that you can't really get in the wild, making the chimps be more aggressive against each other so the yummies are all theirs.

Whether chimps act war-like because of us, or because they simply know no other way, we don't know for sure. Probably because if we get too close to them when investigating, we risk our faces becoming chimp dinner.

How do sharks navigate?

There's plenty about sharks we don't know, like how exactly they navigate the ocean. Despite much of it being dark, empty, watery space, sharks can effortlessly go wherever they need to go, sometimes over thousands of miles, without getting lost. We're flummoxed as to why, and science is no closer to a definite conclusion now than we were years ago. 

Scientists from the Scripps Institution of Oceanography and Birch Aquarium in La Jolla, California, think it has to do with the sharks sniffing their way home. According to National Geographic, Scripps' scientists took several wild leopard sharks, moved them roughly six miles from where they typically Jaws and chill, stuffed cotton balls in some of their noses, and released them in the opposite direction of their stomping grounds. The ones without cotton in their nostrils righted themselves immediately and swam right to their hideout, while the ones who couldn't smell wandered much more aimlessly, swimming slowly and taking forever to get anywhere. This suggests that sharks sniff out, as National Geographic puts it, "chemical molecules found in higher and higher doses nearer to land," to get them where they wanted to go.

But despite the experiment's findings, not everyone's convinced — marine biologist Kim Holland from the University of Hawaii at Manoa thinks the cotton-ball sharks' confusion was due mostly to having stuff up their noses they didn't expect and panicking as a result. Meanwhile, sensory biologist Jayne Gardiner, from the New College of Florida disputes the chemical idea, suggesting that sharks smell what's on land, using changes in light and temperature as clues they're near the finish line. For now, both sides' guesses are as good as any.

Why do animals play?

It seems like the easiest conclusion in the world: animals play because it's fun! More than that, they learn stuff by doing so. Play-fighting teaches them how to fight for real, playful romps build lifelong friendships, and the like — everyone knows that, right? Well, as it turns out, we actually know nothing definitive about why animals play because, when you break it down, the very idea makes very little sense. 

As Lynda Sharpe of Scientific American points out, having fun can easily prove costly if you're an animal. At best, it's a time waster — there's food to be foraged and babies to make, not to mention dangers and predators everywhere. So why spend precious moments messing around when you could be hunting, mating, or surviving? Plus, as Sharpe learned by observing various animals, the idea that play equals learning hadn't really been tested before being accepted in popular culture — when she did, she discovered that young animals didn't actually learn many skills from it.

So there must be a real reason behind why animals play. But of the many theories out there, none are solid enough to be accepted as fact. Some researchers have found that certain species who play handle stress better, or grow up to be more independent, but that's not across the board with all species. As University of Tennessee at Knoxville biologist Gordon Burghardt said regarding play (as quoted by National Geographic), "there are so many different kinds of play that there might not be a single function." So perhaps that's why animals play: for this reason or for that. But right now, we can't even agree on that.

Why do crows hold grudges?

Crows are scary smart and, as it turns out, scary petty. As researchers in Seattle learned in 2011 (according to LiveScience), not only do they remember the faces of humans who held them captive, they'll foster grudges to the point where — years later — they'll attack, peck, and dive-bomb their ex-captors. To a crow, revenge is a dish best served forever. 

Why they do this, however, is unknown. Crows could just as easily forgive and forget, yet they don't. There don't even appear to be many theories as to why, even though we don't really know. We know crows have incredible memories, but why they insist on attacking somebody they don't like, years later, we have no clue. So instead, researchers at the Proceedings of the National Academy of Sciences are focusing on ways to keep the crows from dive-bombing people into oblivion, such as treating them better while in captivity. Whether that works to curb their revenge-fueled minds remains to be seen, but it certainly never hurts to be nicer to animals. Especially the ones who remember.

Why do lonely ants die so quickly?

Ants are incredibly social creatures — if you run into one, chances are there's about 15 million more nearby. But as it turns out, they're not just social because there's strength in numbers, but because if an ant's left alone, they will literally die, and do so super-fast. 

In a study conducted by researchers from University of Lausanne Switzerland (recapped by The New Yorker), a species of carpenter ants known as Camponotus fellah was shown to suffer significant effects of being isolated from other ants. Where social ants would survive over two months (their average life span being 6-12 weeks), the lonely ones would die off after a mere six days. They were some sad, sad fellas.

These ants were observed walking much more than social ants, and they ate much worse. They took in just as much food as social ants, but much of it never left the crop area (the part of their stomach that stores food meant to be regurgitated for family), meaning they ate a lot, but very little wound up in their digestive tracts. In short, they wandered everywhere, like little lost souls, then ate poorly and all but starved to death.

Why this happens, scientists don't know. It certainly sounds like depression, but why do their digestion habits change so much? Why does food uselessly stay in the crop, as opposed to going toward the only ant who could benefit from it? Why are the ants walking so much? Are they looking for family, as the study theorizes? Right now, all that's certain is that the story of a lonely, wandering ant absolutely needs to be made into a country song.

Why are Great White shark migrations so weird and disorganized?

We know less about Great White sharks then we do regular sharks, mainly because every time we try to study one in captivity, they die fast. One of the biggest mysteries about great white behavior is where exactly they go, and how they get there. 

As National Geographic points out, Great Whites have possibly the weirdest migration patterns of any shark. Rather than everybody going in roughly the same direction, Great Whites tend to zig-zag here and there in random, seemingly disorganized fashions. Some stay near coasts, others wander into the deep centers of the ocean. Some move north for the summer, and south for the winter, like birds might — but not all do this. Males, females, and cute little shark kids all seem to follow different paths as well.

Scientists have managed to figure out, via tagging, where many of these sharks go — Great Whites from California and Mexico wind up in the middle of the Pacific at a place biologist Salvador Jorgensen cleverly dubbed "Burning Man for white sharks." But we still don't know why they take such divergent paths to get there, or what they're doing there. Mating, perhaps? We're not sure, because that area's both large and incredibly deep, so monitoring a tag is all but impossible. Plus, it seems like males and females don't hang out together for very long, so either they're not mating, or get it over with as quickly as possible — because even Great Whites aren't actually attracted to Great Whites.

Then, adding to the mystery, is how sharks elsewhere migrate even more randomly. Great Whites in Australia, for instance, migrate to the coast usually, but don't have a "Burning Man" area where they all converge to do … something. It's real hard to figure out a species when the species seems to follow fewer patterns than a Pollack painting.

How do young cuckoo birds know exactly where to migrate?

Usually, bird migrations aren't hard to figure out: kids follow mama to wherever they need to go. In the case of cuckoo birds, however, it's a tad different. For one thing, they don't really have "moms." A female cuckoo will lay her eggs, then deposit them in another bird's nest, then fly off to party, probably. Meanwhile, the egg hatches, and the chicks are raised by a completely different species, like a real-life Dinosaur Train

The baffling part, however, is how these cuckoos, who've not been raised by any other cuckoos and won't encounter any other cuckoos along the way (they tend to fly solo), know instinctively where to migrate and how to get there. Despite no family or flock, they all wind up in Africa for the winter, and nobody knows how they do it. Even when released far away from their traditional routes, like when researchers from the University of Copenhagen moved several cuckoos from Denmark to Spain and then set them loose, they still managed to make it to Africa. So while we know they can do it, we still don't know how they can do it with no help whatsoever.

One theory, as put out by Quartz, suggests that because cuckoos evolved in Africa, the location is embedded in their DNA. While it might make some sense, that idea hasn't been proven. For all we know, they simply sense it's cold, then fly in the opposite direction until it's nice and warm. But even then, why don't they wind up in other warm places, like South America or Australia? Why always Africa? Hopefully someone learns the answer soon, because the suspense is driving us cuckoo.