In school we were taught that when autumn comes, the birds head south. In reality, the picture is far from being so clear. First, not all species migrate. It might seem that migrations are related to the onset of cold weather and food shortages, but there are some birds that head south regardless of these conditions. Migrations can be both grand, from continent to continent, and local, from the top of a mountain to a warm valley. Bird migration is a complex process, which scientists do not fully understand. But Aristotle wrote that some birds "disappear" in autumn. However, he interpreted this fact in a surprising way, seeing in it the transformation of some species into others.
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Now we know exactly what's going on. In addition, the flight paths of the birds are being traced, establishing the traditional routes. Some of them turn out to be very challenging. And the record for uninterrupted flight is held by the spotted eagle, whose male flew 12 km from Alaska to New Zealand without landing. And breasted warblers fly only 200 km, but keep in mind that these birds, even with feathers, weigh less than 3.200 g and fly from the US to Venezuela without even stopping to drink water.
But we don't know exactly how birds know where south or north is and which way to fly. Scientists believe that there are several ways to find your way home. Yes, a "winter" home doesn't look like a temporary home for birds. And the locals believe that it is their birds that have come home.
Of course, birds don't know how to use a compass, and they certainly don't have maps. We are the ones with navigators and other electronic devices to chart your path. Birds are guided by their natural instincts. It is interesting that in some species the young fly south first and the older ones do so later. There isn't even anyone to show them the way. So, from the moment they are born, the birds somehow know where to fly. The flight itself is well planned; even the wedge shape is no accident: early birds create air currents to help other conspecifics. And some species store energy-dense fat in their bodies before they fly, so they don't have to think about food for weeks.
Scientists have even conducted various experiments. In one of them, the storks were captured shortly before a seasonal flight and taken far from their home. But the birds immediately flew in the right direction for them. Another interesting experiment was carried out with English ducks. They traditionally spend the winter in their home country, but in this case the eggs were brought to Finland. In this country, ducks perform seasonal migrations. And, having been born in the new country, the English ducks also flew south, as is the custom here.
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How do birds know where to fly?
The most popular theory is that birds react to Earth's magnetic fields. Magnetic lines are known to connect the poles. Perhaps it is these guides, invisible to our eyes, who guide the birds. To test this theory, magnetic plates were attached to the pigeons, observing changes in flight orientation. It turned out that the birds became actually worse at understanding the direction of movement, although they couldn't completely mislead them. Birds are known to contain magnetite in their beaks. This iron-containing mineral acts like a compass.
Another possible way of orienting is through landscape features: clumps of trees, river bends, mountains, coastlines. Perhaps the birds and the position of the sun are taken into account and, at night, the moon and the constellations. The mention of night is not accidental: this time of day is the best for flying, because the wind calms down. During daylight hours, migratory birds use daylight to orient themselves, which is polarized by gas molecules. As a result, on a clear day, birds can see some directional streaks in the sky. When the sun is in the west, the lines go from north to south, which helps with orientation.