How do birds know
 where to go when they
 migrate?

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Blackpoll Warbler

Imagine a bird that weighs as much as a ballpoint pen and is a better athlete than you. Make that a better athlete than any human, living or dead. Of course, these Blackpoll Warblers don't look like super athletes. In fact, they look like the kind of birds you might see at the feeder and not give a second glance. They're only about four inches long, with an olive green cap on their head and white bars on their sides. But these warblers make a journey across the Atlantic Ocean from North America to South America in a single marathon flight. No food, no water, no rest for three days. That's over 2,200 miles of flying all at once, at speeds over 20 miles per hour! And did we mention that they don't float and aren't waterproof? So if they hit the water, they're dead.

Runners

So how does that make a Blackpoll Warbler a better athlete than any human? Well, let's look at it this way: What's the fastest you can run a mile? Maybe six or seven minutes? Maybe faster if you're a great runner. The fastest runners in human history have run a mile in just under four minutes. Well, for you to perform an athletic feat the equivalent of a bird flying nonstop for several days, you'd have to run a mile in about four minutes. And then keep running four-minute miles for 80 days!

Hey-if you want to try it, be my guest. You'll break a lot of records along the way. But you're not going to catch up with these birds. Since they're so small, their journey between continents is equal to about 35,000,000 of their body lengths. So let's say you're a five foot tall human. Then 35,000,000 of your body lengths would be over 33,143 miles. More than once around the Earth! It's exhausting just thinking about it.

Why Bother Going South?
So why would these little birds make such a challenging journey? Well, like most birds and some mammals, fish, insects, amphibians and reptiles, they are making a seasonal migration. They spend the summer in the north, head south in the fall as cold weather approaches, spend the winter in the south, then head north again when the weather gets warmer in the spring. Since the climate of our planet varies greatly as you go from the North or South Pole to the equator, mobile animals are able to move around to live in the climate that they prefer.

Broad-winged Hawk

But is it really worth all that effort just to have warmer weather in the winter? Well, that depends on what the critter prefers to eat and whether they can still get it here in the winter. Let's say you chow on insects, like the Blackpoll Warbler. A nice, juicy worm or mosquito is your idea of a Happy Meal. The problem is, there isn't a worm or mosquito to be found when it's 20 degrees F and two feet of snow. So you follow the insects and migrate south. If you were a raptor like a Broad-winged Hawk and ate small mammals, amphibians and reptiles, you'd face the same problem. Some animals die off by winter, while many others take cover and it simply gets harder to hunt them down. So the benefits of warm weather and more abundant food in the south might outweigh the cost of making a migratory journey.

Wild Turkeys in winter

Unless of course you have a brilliant strategy for adjusting to winter. Since not all birds migrate, obviously the ones that stay in a place all year must have some way of surviving. Many of them are more dependent on plant foods or shift their diet to become more dependent on plant foods. Wild turkeys eat persistent fruits in the winter, such as wild apples or barberries. But one of the craftiest year-round residents has to be Downy Woodpeckers, who stash food to eat when they need it in winter. Imagine all the times you've walked through the woods in the winter without realizing you were in a Downy Woodpecker superstore-all those nuts and even insects tucked away in holes, crevices and cracks in the bark.

It all comes down to meeting your basic needs-food, water, shelter, and space-in your habitat. If conditions change-it grows colder, your prey disappears-then you either change your game plan or hit the flyway and travel to extend your habitat.