How Do Birds Know Where To Migrate?

It's long been one of nature's greatest mysteries: how the heck do birds know where to go for the winter? If most humans tried to migrate south without a map or a GPS, we'd probably end up in Nova Scotia. 

Scientists have been trying to solve this mystery for a long time. Even Aristotle, renowned smart person, was baffled. According to Mental Floss, he actually thought birds just changed species for the winter, which is a handy way of explaining why the garden warbler population gets replaced by a bunch of blackcaps when the weather starts to change. So, maybe he wasn't actually as smart as we all thought he was. 

Some species of bird are known to migrate ridiculously long distances — the arctic tern travels from Greenland to Antarctica, which is roughly 44,000 miles. And you thought it was tough walking from the back of the parking lot all the way to the front door of Target in January. 

So how do they do it? The answer is, well...we still don't really know. We do have some clues, though. Birds undergo behavioral changes that appear to be triggered by photoreceptors in their brains. As the days get shorter, they eat more and become restless, and this happens even if they're kept in a cage. But still: how do they actually know where to go? A 1978 study found that captive birds that couldn't see the sky still experienced migratory restlessness, and preferred to fly in the same direction as non-captive birds of the same species. Researchers concluded that they were using "external orienting cues, probably of the earth's magnetic field." 

Just how they're able to sense that magnetic field is still the subject of research, though. National Geographic explains that some species have special molecules in their eyes that can sense planet Earth's magnetic field. Those molecules are linked to the parts of the animals' brains that process visual input, which means they can literally see the Earth's magnetic field. Other birds seem to have different ways of knowing where to go. Pigeons may use their sense of smell to guide them, and some other species just learn their migration patterns from the previous generation.

The methods different birds use to get to the right place also appears to be influenced by genetics. In 2008, researchers decided to confuse the heck out of a bunch of poor birds by crossbreeding species with different migratory patterns and then laughing while their offspring blundered around in the sky trying to figure out where they were supposed to go. The result was a bunch of birds who tried to take the middle road between each parent's migratory path.

So at the end of the day, we're a little closer to understanding how birds do that amazing thing they do every winter, even though we still have to work out some of the details. At least we've pretty much ruled out the whole changing species thing. Sorry, Aristotle.