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How do birds navigate during migration?

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📓 The short answer

Birds navigate by developing an internal map of visual and scent landmarks. Also birds rely on sun and star positions to orient themselves. Additionally, birds use Earth’s magnetic field, which they can possibly sense through tiny magnetic particles in their beaks or potentially "see" using a special light-sensitive protein in their eyes.

📚 The long answer

Birds don't have Google Maps.

Yet somehow they migrate hundreds, or even thousands, of miles without getting lost.

We know that birds either learn migration routes from older birds or inherit the distance and direction of their migration in their genetic code.

But if you want to get from point A to point B, you need a map and a sense of direction. Let's start with bird maps.

Birds need a map

During a bird's first migration, it builds out a mental map which will enable it to make the same journey year after year. They identify visual landmarks along the way, like rivers, mountains, and forests. Birds also use scent landmarks to recognize familiar locations.

While not all birds survive their first migrations (~30% of songbirds don't make it back 😢), those that do are equipped with a detailed map to guide them on their subsequent journeys.

Birds need a sense of direction

Birds have a few tricks up their wings to help them navigate. Research has found that birds are equipped with at least three compasses, some of which are similar to how ancient humans used to navigate.

Compass #1: Sun compass

Scientists have determined that birds use the sun to navigate. They sense the sun's position in tandem with their internal circadian clock to understand the time of day, which helps them adjust their flight direction accordingly.

Compass #2: Star compass

Also like human navigators, birds seem to use stars as cues to navigate. During nighttime migrations, birds utilize a star compass by recognizing star patterns and constellations, particularly around the North Star, which remains nearly stationary.

Compass #3: Magnetic compass

Studies have also suggested that birds have a magnetic compass. In an experiment observing how birds oriented themselves, a device was placed around covered bird cage that shifted the direction of the Earth's magnetic field. When the magnetic direction changed, so did the birds change their direction.

Two hypotheses explain how this magnetic compass works in birds: a mechanical sensor and/or a chemical sensor.

🧲 Mechanical Sensor Hypothesis

Some birds, including homing pigeons and chickens, have been found to have trace amounts of magnetite particles in their beaks. Magnetite, as the name suggests, is a highly magnetic iron oxide crystal that aligns with magnetic north. So it's possible that birds might sense magnetic pull through magnetite particles in their beaks.

Interestingly, some bird breeders buy magnetite powder to feed it to their birds in an attempt to increase the homing power of their offspring.

🧪 Chemical Sensor Hypothesis

​Recent research has discovered that birds have a light-sensing protein in their eyes, known as cryptochrome, which may allow birds to literally see magnetic fields. This fascinating capability is thought to be based on a quantum phenomenon known as the radical pair mechanism.

When cryptochrome absorbs light, it undergoes a chemical reaction that results in a pair of molecules, each with an unpaired electron. These molecules, known as free radicals, form what's called a radical pair. Because both radicals are created simultaneously, their unpaired electrons become quantum entangled. This means the electrons' properties are interconnected, so a change in the state of one electron instantly affects the other, no matter how far apart they are.

So, what does this have to do with bird navigation? The quantum state of these radical pairs is highly sensitive to magnetic fields. Depending on the alignment of the Earth's magnetic field, the entangled electrons can switch between different quantum states.

These states influence chemical reactions, potentially signaling the bird's brain via the cryptochromes to "see" magnetic fields.

Here's how researcher Henrik Mouritsen describes it: "So maybe it's kind of a shadow on top of whatever else you would be seeing as a bird, but what exactly the bird is seeing we do not know because we cannot ask the bird."

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

📖 Book of the week

​Infamy: The Shocking Story of the Japanese American Internment in World War II by Richard Reeves​

Shortly after the attack on Pearl Harbor, the U.S. government did the constitutionally unthinkable: it forced nearly the entire population of residents of Japanese descent (many American-born citizens) into what they literally called "concentration camps." This book details this dark period of U.S. history, providing heartbreaking personal accounts in the camps, insight into how the government tried to justify the stripping of personal freedoms, and stories of heroism of Japanese-American soldiers fighting on the front lines during World War II despite this mistreatment.

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​Check out the full list of books I've recommended here.

👀 Catch up on other curious questions

• ​Why do birds chirp in the morning?​​
• ​How does your phone track steps?​​
• ​How did early Polynesian explorers find islands?​​

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