Why whale songs travel across oceans and change every year

HostWhen you look out at the ocean from the beach, it seems like this vast, quiet space. You might see some waves or a boat, but it feels like a world of silence once you get below the surface. But if you were to take a special underwater microphone and drop it deep down, maybe half a mile or so, you would hear something that sounds almost impossible. You could hear a whale singing from thousands of miles away. It's not just a faint noise, either. It’s clear, like the water is acting as a natural fiber-optic cable for sound. How does a living thing send a message across an entire ocean basin like that?

GuestIt’s all about a specific slice of the ocean called the SOFAR channel. That stands for Sound Fixing and Ranging channel. Think of it as a hidden highway for sound that sits deep underwater. To understand why it works, you have to look at two things that change as you go deeper: how cold the water is and how much the water weighs down on you. Near the top, the water gets colder as you go down, and cold water slows sound down. But as you get even deeper, the weight of all that water above you, the pressure, starts to build up. High pressure actually speeds sound back up. Right in the middle, between six hundred and twelve hundred meters down, those two forces find a balance. This creates a layer where sound moves at its slowest possible speed.

HostThat seems like it would do the opposite. If the sound is moving slow, wouldn't it just fade out faster?

GuestYou’d think so, but it actually traps the sound. When a whale sings in that layer, the sound waves try to scatter up toward the surface or down toward the floor. But because of how the water is layered, the waves keep getting bent back into the center of the channel. It’s called refraction. Instead of the sound getting lost in the wide open sea, it stays focused in that one flat layer. It can travel for thousands of miles with almost no loss of energy. It’s like a long, liquid pipe that carries the song from one side of the world to the other.

HostSo the ocean provides the highway, but the whales still have to be incredibly loud to fill it. I mean, we make sound by blowing air out of our lungs and through our throats. If a whale did that for twenty minutes, they’d run out of air and have to come up for a breath, right?

GuestThat’s the wild part. They don't have to exhale to sing. Humpback whales have this specialized setup in their throat. There’s a big U-shaped fold of tissue that works a bit like our vocal cords, but they don't let any air out while they use it. Instead, they have a large, stretchy bag called a laryngeal sac. To make a sound, they just push air from their lungs into that bag and then move it back again. They’re basically recycling the same breath over and over internally. Since they aren't blowing bubbles or losing air, they can keep those low, heavy shakes going for a long time. It creates a deep kind of resonance that’s perfect for that underwater highway.

HostSo they’re basically just hummers. They keep it all inside. But when we hear these songs, they aren't just random noises. They sound like they have a real pattern to them. Does every whale just have its own favorite tune?

GuestActually, they're strict conformists. In any one group of whales living in the same area, every single male is singing the exact same song. It’s not like birds where one might have a slightly different trill. They all follow a very rigid structure. The songs are built in layers. You have small sounds that make up a phrase, then those phrases make up a theme, and then a few themes in a row make the full song. If you’re a male whale in that group, you have to sing the current hit single. If you don't, you might not be recognized as part of the group or you might not be able to compete for a mate. They want to be on equal footing, so they all stick to the script.

HostThat sounds a bit boring for them. If they all sing the same song, does that mean the song stays the same forever?

GuestNot at all. The songs are always changing, just very slowly. Maybe a phrase gets a bit shorter one year, or they add a new little sound at the end. It’s a bit like a game of musical telephone. But every now and then, there’s what we call a cultural revolution. A totally new, catchy song will show up, usually from a different group of whales from a different part of the ocean. When the local whales hear this new tune, they drop their old song almost instantly and start singing the new one.

HostHow does a new song even get there? If they’re thousands of miles apart, it’s not like they’re hanging out at a club together.

GuestIt ripples across the sea. Researchers have watched this happen in the South Pacific. A new song might start with whales off the east coast of Australia. Then, a traveler moves east and sings that song near a new group. Those whales pick it up, then someone from that group moves further east, and the song keeps jumping. It moves like a viral trend all the way to French Polynesia. It’s like a hit song from a different country taking over the radio until everyone is humming it.

HostIt’s amazing to think that while we see a quiet, empty blue surface, there are these massive songs moving through the deep water like a game of telephone.

GuestSome of these songs are so catchy and travel so well that a single new tune can completely replace every other version in an entire ocean basin in just one or two seasons.

HostThe next time I look at the waves, I’ll be thinking about that deep-sea highway and the fact that, right underneath the boat, a whale might be learning the latest hit song from a traveler halfway across the world.