subscription
apple | Spotify | Amazon | love radio | player.fm | tune in
cast box | poturama | Podcast Republic | RSS | patrain
Podcast Transcript
Every year, hundreds of millions of birds migrate around the world.
Some migrate very short distances, some migrate very long distances, and some don’t bother to migrate at all.
For centuries, people didn’t know why birds migrated, how they traveled such long distances each year, or where they went.
Thanks to modern science and technology, we now have a better understanding of how it works and where it goes.
Learn more about bird migration in this episode of Everything Everywhere Daily.
Bird migration—assuming the internet theory is wrong and birds do exist—is one of nature’s most incredible feats of navigation.
Before I go into detail about the how and why, I should probably first explain the what.
Migration is simply the seasonal movement of animals, almost always during the summer and winter months. It is almost always between areas used for breeding and/or feeding.
Birds aren’t the only animals that migrate. There are other animals that also migrate, such as wildebeest, reindeer, whales and butterflies. However, none of them achieve the migratory achievements of birds.
For a long time, humans didn’t know that birds migrated. Because people couldn’t travel very far, they only saw half of the migration story. They know that birds disappear at certain times of the year and then come back.
Where they went and why they left is hotly debated.
Aristotle had several different views on what happened to birds when they disappeared.
He believed that swallows hibernated in the mud during the winter. He thought redstarts turned into robins in the winter.
Likewise, Aristotle knew that cranes were reported to fly annually from the northern Black Sea to the marshes along the Nile.
Not everyone is confused by the birds’ movements. Ancient Polynesians used bird migration and flight direction to aid navigation.
Nonetheless, Aristotle’s theories persisted into the Middle Ages and beyond, even though they were wrong.
By the 18th century, most Europeans believed that swallows hibernated through the winter, although there was no evidence that swallows actually hibernated.
The sailors’ reports began to change the naturalists’ minds. They reported seeing swallows flying north over the Mediterranean Sea.
In 1822, a stork was discovered in Germany, shot with an arrow made of African wood. The only way it got there was by being shot in Africa thousands of miles from where it was found.
The phenomenon of bird migration became generally accepted in the mid-19th century after extensive observations of birds in different parts of the world at different times of the year.
Bird migration is an evolutionary strategy that has developed over millions of years.
There are several reasons for migrating, and there are some drawbacks to this strategy.
The most obvious reason for migration is food. Many birds migrate to areas where food is abundant, especially during the breeding season. For example, insectivorous birds fly to northern latitudes in the spring and summer when insects are plentiful, then return to warmer climates in the fall and winter when northern food sources are reduced.
Bald eagles migrate, but not like other birds. They will spend the summer in the far north and then fly south to where they won’t freeze over in the winter. Eagles can tolerate fairly cold temperatures, but they need to eat, which they can’t do without access to lakes and rivers.
Other birds do migrate in response to temperature. They never developed the ability to insulate themselves in cold climates, so they had to leave.
One of the main reasons for migration is reproduction. Birds fly to certain nesting areas each year. In at least one case, the fact that certain species of birds migrated to the reserve to breed may have saved them.
Whooping cranes were once abundant in North America, but their numbers have been reduced to near extinction due to habitat loss.
However, a small group managed to survive, but no one knows where their nesting site is.
In 1954, they discovered the whooping crane’s hideout. The species’ only remaining natural breeding habitat is found in Wood Buffalo National Park in northern Alberta, Canada.
Wood Buffalo National Park is a very large national park, the largest in North America, and very difficult to access. Most of the park is wetland and is inaccessible during the summer.
Whooping cranes migrate there in the summer and breed in a completely protected area. The locals who live there don’t even know the cranes are there because they can only access the area in the winter when the water freezes and the cranes disappear.
Once one accepts that some birds undergo seasonal migrations, the really big question is how to proceed. Naturalists eventually realized that certain birds migrated across a large portion of the Earth every year.
Bird migration is not completely understood, but there are several popular theories about how they travel long distances.
The first is endogenous programming.
Endogenous programming in bird migration refers to the innate genetically encoded behavioral and physiological processes that guide the migratory activities of birds. This internal programming determines when birds migrate, where they go and how they get there, independent of environmental factors.
Most birds have an internal body clock, or circadian rhythm, that tells them the best time to begin migration. This clock is affected by hormonal changes, which are triggered by changes in daylight length. These hormonal changes affect behavior and physical conditions, such as fat storage, in preparation for their migration.
Much of a bird’s migratory instincts are encoded in their genes. Research shows that migratory behavior is heritable. Studies involving crosses between migratory and non-migratory birds have shown that offspring inherit migration direction and distance, suggesting that migration patterns have a strong genetic component.
However, many ornithologists believe there is more to it than that. There are built-in mechanisms that help birds navigate.
Some birds contain tiny magnetic particles, usually iron oxide called magnetite, in their beaks or brains. These particles are thought to act like tiny compasses. Studies have shown that these particles can help birds detect Earth’s magnetic field, providing a sense of direction. This is called the magnetite-based hypothesis.
Another famous theory involves cryptochromes, light-sensitive proteins found in the retinas of migratory birds. These proteins may enable birds to literally see the Earth’s magnetic field as a visual pattern covering their normal field of view, often assumed to be a visual “map.” This light-dependent mechanism is thought to be affected by the wavelength of light, particularly in blue light.
However, birds can sense magnetism, which can be more complex than simply knowing which direction is north or south.
Unlike a compass, which shows magnetic poles as horizontal attractions pointing north and south, birds are sensitive to the tilt of magnetic field lines. This means they can detect the angle at which these lines intersect the Earth.
One of the reasons we know this isn’t just endogenous programming is because the magnetic field around the birds was artificially altered in the experiment. These experiments suggest that changing magnetic field conditions may confuse migrating birds, affecting their ability to orient themselves correctly.
This strongly supports the theory that birds rely on the Earth’s magnetic field to navigate.
Most birds migrate in flocks. There are several good reasons for this. The first is related to energy conservation.
For example, when geese fly in a V formation, they expend about 20% less energy than when flying alone. This is the same principle why cyclists lag behind the leaders who take most of the wind resistance.
Another reason is safety in numbers. If you fly in a group, some people in your group are more likely to survive than if you are traveling alone. If you have a large enough group, you can also deter predators from attacking.
Despite their strong desire to migrate, there has been a recent phenomenon of birds no longer migrating. This has happened to some Canada goose populations.
Geese in urban areas began to stay put during the winter instead of flying south.
Urban environments often provide abundant food sources, such as grasses in lawns and parks, and man-made water bodies that do not freeze over in the winter, such as heated ponds on golf courses and parks. These conditions reduce the need for immigration.
The problem is that when geese stay put, their offspring may lose the knowledge of migration, meaning they may stay in place forever.
As I mentioned before, every migratory bird has a completely different migration pattern.
Arctic terns have one of the most impressive migrations of all species. It is the longest migratory bird in the world, traveling approximately 71,000 kilometers or 44,000 miles each year between its Arctic breeding grounds and the Antarctic coast.
Arctic terns are a circumpolar species, meaning they are found throughout the Arctic regions of North America, Asia, and Europe. Therefore, they choose multiple routes to fly to Antarctica every year.
The tagged birds were found to have flown along the east-west ocean as they traveled from the Arctic to the Antarctic and back.
By comparison, the bird considered to have the shortest migration is the North American blue grouse, also known as the dusky grouse. They live in the Rocky Mountains of the western United States and Canada. They are terrestrial birds and can only make short flights.
They migrate only a few hundred meters up the mountain each year. The strange thing is that in winter they go up the mountain instead of down.
What would you do if you were a bird from East Asia and your flight south was blocked by the Himalayas, the highest mountain range in the world?
Bar-headed geese flew right over them. They are known for flying over the Himalayas during their migration, reaching altitudes of up to 6,500 meters or 21,300 feet, where oxygen levels are very low.
The black-headed warbler is a small North American songbird that makes one of the most arduous flights of any migratory bird, flying 2,700 miles (4,350 kilometers) non-stop from New England to South America.
They are suspected of feeding on insects while flying.
Not all birds that fly long distances migrate. Some birds are simply nomadic, moving from one place to another whenever conditions are right.
Flamingos and albatrosses are two birds that can fly thousands of miles but don’t actually migrate. They are constantly traveling, and whenever food becomes scarce, they move upward, usually in an east-west direction.
Bird migration is one of nature’s greatest wonders. Through a combination of genetic programming and the ability to read magnetic fields, these dinosaur descendants were able to pull off some of the most impressive nautical feats in the animal kingdom
