How female dolphins know which males to avoid - National Geographic

Marina: Welcome back to Deep Voices — I'm so glad you're here. I'm Marina, a marine biologist who has spent the better part of two decades completely in love with whales and dolphins, and this is the show where we dive into their world — their songs, their languages, their cultures, and the extraordinary science trying to understand what they're actually saying. Marina: Before we get into today's stories, a huge thank you to our sponsors: Ada, who helps businesses integrate A I into their workflows in smart, practical ways; Ago Consulting — pronounced "Ahh-Go" — silicon development experts working across everything from A I to full system-on-chip design; and Zen Semiconductor, an umbrella company with a whole portfolio of businesses across the silicon industry. We genuinely appreciate their support — it's what keeps this show swimming. Marina: Okay. Today we have a really remarkable set of stories. We're going to talk about how female dolphins essentially built their own social radar to filter out bad-news males — and it is fascinating. We're going to look at new physics around whale song that sounds almost impossibly strange. And we're going to visit the sperm whales of the Mediterranean, where scientists have discovered something incredible about how dialects change over time. Let's go deep. Marina: So let's start with VOICES OF THE DEEP — and today I want to begin with something that honestly stopped me in my tracks when I first read about it. Scientists studying bottlenose dolphins have been looking at how female dolphins know which males to avoid. And when you dig into it, it turns out the answer is deeply, beautifully social. Marina: Here's the thing about bottlenose dolphin society — it's complicated in ways that would make a sociologist's head spin. Male bottlenose dolphins, particularly in places like Shark Bay in Western Australia, form these intricate alliance networks. You have pairs and trios of males who work together to court females — and sometimes that "courting" is coercive. Males in alliances will herd females, essentially keeping them close against their will. Marina: Now, for a long time researchers focused a lot of attention on the males — their alliance structures, their strategies. But more recent work has started asking the other question: what are the females doing about all this? And it turns out, a lot. Marina: Female dolphins are paying close attention to the social world around them. They watch. They listen. They learn which males are reliable, which are aggressive, which ones tend to show up together and behave in threatening ways. And they use their own social networks — their friendships with other females — to essentially share that information. Marina: Think about what that means. These aren't just individual animals making individual choices. They are embedded in a community that collectively processes social information. A young female dolphin isn't starting from scratch — she's learning from the females around her who has a reputation for what. Marina: And here's where it connects to communication in such a direct way. Dolphins produce a huge variety of vocalizations — clicks, whistles, burst-pulse sounds — and they also pay close attention to each other's signature whistles. Every dolphin has one, a unique call that's essentially their name. And females appear to track which male whistles are associated with which kinds of behavior. It's acoustic reputation management, in a way. Marina: There's also fascinating research showing that females in alliance-heavy environments like Shark Bay synchronize their behavior with trusted companions — they swim together, they surface together, almost like there's safety in coordination. It's not just emotional bonding, though that's real too. It's a practical strategy. Marina: What moves me about this research is how it reframes the story. For so long, the narrative around dolphin society has been about male competition and strategy. And yes, that's real and interesting. But the females have been running their own complex social intelligence operation the entire time — and we're only just beginning to fully appreciate how sophisticated it is. Marina: Now. Let's talk about something that bridges the physical world and the acoustic world in a way that I find almost poetic — and that's the question of how a whale's dive shapes its song. Marina: Researchers at Syracuse University have been looking at humpback whales — the great singers of the ocean — and asking a question that sounds simple but turns out to be anything but: does the depth at which a whale sings change what its song actually sounds like? Marina: And the answer, it turns out, is yes — in really interesting ways. As a humpback whale dives deeper, the pressure around it increases. And that changing pressure affects the whale's body, including the structures it uses to produce sound. So the song that comes out at two hundred meters down is not acoustically identical to the song produced near the surface. Marina: Now, humpback males sing these long, elaborate sequences — they can go on for hours — and we know those songs change over time as cultural trends sweep through populations. But this research adds another layer: the physical act of diving is itself shaping the acoustic output in real time. Marina: What that means for how we interpret recordings is significant. If you're listening to a hydrophone recording and you don't know where in the water column the whale was singing, you might be misreading things. Two whales singing the same phrase at different depths could sound different to our instruments. And to each other. Marina: There's a question buried in here that I love: do whales know this? Are they compensating for pressure changes as they sing? Are they modulating their output to keep the song consistent, the way a trained singer adjusts their voice on stage versus in a studio? We don't fully know. But the fact that we're even asking it says something wonderful about where cetacean research is heading. Marina: And then — okay, I have to tell you about this because it is one of the most brain-bending things I've come across in a long time. Whale song appears to travel faster than the speed of sound. And somehow — somehow — this does not break Einstein's theory of special relativity. Marina: Here's what's happening. Sound in water doesn't travel at a fixed speed. The ocean is layered — warmer water near the surface, colder and denser water below — and those layers refract sound. There's a layer called the SOFAR channel, which stands for Sound Fixing And Ranging, and it acts like a natural acoustic highway deep in the ocean. Sound gets channeled along it and can travel enormous distances. Marina: What researchers have found is that under certain conditions, the apparent propagation of whale song — the way the wave pattern moves — can exceed the local speed of sound. It's what's called a superluminal phase velocity in physics terms, and it's a real phenomenon that also occurs with light in certain contexts. Marina: But here's the key: no information or energy is actually traveling faster than the speed of sound. It's the wave pattern, the shape of the signal, that appears to move faster — not the actual physical disturbance. It's a bit like if you swept a laser pointer across the moon really fast — the dot of light can move faster than light itself, but no actual photon is making that trip. The rules are intact. Einstein is fine. Marina: What it does mean for whales is that their songs — already some of the most extraordinary acoustic achievements in the animal kingdom — are behaving in ways that involve genuinely complex physics. The ocean is not a passive medium for their communication. It is an active participant, bending and channeling and in some cases apparently accelerating the patterns of their voices across hundreds of miles. Marina: That image just floors me. A humpback singing somewhere in the North Atlantic, and the pattern of that song rippling outward in ways that touch the edges of relativity theory. Nature is so much stranger and more wonderful than we give it credit for. Marina: Alright — let's move into our second thread. CULTURE AND DECODING. And I want to center this on sperm whales, because the news out of the Mediterranean right now is genuinely exciting. Marina: Scientists have been studying sperm whale populations in the Mediterranean Sea and they've found something remarkable: the whales there have their own evolving dialects. Now, sperm whales communicate using clicks — sequences called codas. Different clans of sperm whales around the world have different coda repertoires, almost like regional accents or languages. We've known this for a while, thanks in large part to researchers like Luke Rendell and Hal Whitehead who've spent decades studying sperm whale culture. Marina: But what the Mediterranean study is showing is that these dialects aren't static. They change. They evolve. The Mediterranean population is relatively isolated — the Strait of Gibraltar is a narrow passage, and sperm whales don't move freely between the Atlantic and the Mediterranean — and so this group has been developing its own acoustic culture in relative isolation. Marina: What the researchers found is that the coda repertoire of Mediterranean sperm whales has been shifting over time. New patterns appear. Some older ones become less common. It looks, in structure, remarkably like how human dialects drift — words fall out of fashion, new expressions catch on, and over generations a regional accent can become almost its own distinct dialect. Marina: Now, the question of how this happens in sperm whales is fascinating. Sperm whale society is matrilineal — females and their young live in stable social groups, and young whales learn from the adults around them. The codas they produce, they learned. They weren't born with them. That is culture, in the full biological sense of the word: socially learned behavior that varies between groups and changes over time. Marina: And this is where A I enters the picture in a way that feels genuinely transformative. Project CETI — the Cetacean Translation Initiative — is one of the most ambitious scientific undertakings I've ever come across. Their focus is primarily on sperm whales in the Eastern Caribbean, off the island of Dominica. And what they're doing is deploying an enormous array of sensors — underwater microphones, bio-logging tags on the whales themselves, even small robotic listening devices — to capture whale communication at a scale and resolution we've never had before. Marina: The goal is to collect billions of coda clicks and then use machine learning — large A I models, similar in some ways to the language models that have been making headlines — to find structure in that data. Not to impose human language structure onto whale communication, but to let the patterns emerge from the data itself and then try to understand what they mean. Marina: One of the things that makes sperm whale codas so interesting for this kind of analysis is that they have combinatorial structure. Individual coda types can be combined in sequences, and the context in which they're produced matters — who's present, what the whales are doing, what happened before. That layered structure is exactly what makes them amenable to the kind of analysis A I is good at. Marina: Now I want to be careful here, because this research is ongoing and we don't have translation yet. We can't tell you what a sperm whale is saying. But what we are beginning to be able to say is that sperm whale communication has structure that goes well beyond simple signals — it has something that looks like a combinatorial code, maybe even something like a phonemic system. And that is genuinely extraordinary. Marina: The Mediterranean dialect research and the CETI work in the Caribbean are really two pieces of the same puzzle. One is showing us that these dialects are alive and changing — they have a cultural history. The other is building the tools to actually read them. I cannot wait to see what the next decade brings. Marina: And now — our third thread. A CETACEAN-AND-PEOPLE STORY. And today I want to talk about something that sits at the intersection of welfare, ethics, and the very question of what we owe these animals — because PETA has filed a complaint with the Federal Trade Commission against a dolphin facility in the Florida Keys. Marina: The facility in question is the Dolphin Research Center in Grassy Key, Florida. PETA's complaint to the FTC alleges that the center's claims about conservation and education are misleading to consumers — that people are paying to swim with dolphins believing they're supporting conservation, when PETA argues the reality of the dolphins' lives in captivity is far removed from what those marketing claims suggest. Marina: Now, I want to be thoughtful here, because this is a genuinely complex topic and there are real people on multiple sides of it who care deeply about dolphins. The Dolphin Research Center has been operating for decades and does conduct some research. Facilities like it have historically argued that up-close encounters inspire conservation support and that the dolphins in their care receive excellent welfare. Marina: But the scientific understanding of dolphin cognition and social needs has advanced enormously in recent decades — and that's shifted the ethical conversation. We now know that bottlenose dolphins in the wild have large home ranges. They live in complex, fluid social networks. They have signature whistles — those individual names I mentioned earlier — and they form bonds that last for years, sometimes decades. The social environment of a dolphin is not something you can replicate in a pool, no matter how well-maintained. Marina: There's also research showing that dolphins in captivity can experience chronic stress — elevated cortisol levels, repetitive behaviors, disrupted social relationships when animals are moved between facilities. These are not abstractions. They are measurable physiological and behavioral signals that these are animals with rich inner lives that are not being fully met in captive environments. Marina: What I find significant about the PETA complaint — whatever you think of PETA as an organization — is that it's framing this as a consumer protection issue. It's saying: if people are being told their money is going toward conservation and education, that claim needs to be substantiated. And I think that's a legitimate question to ask of any facility in this space. Marina: At the same time, I want to acknowledge the genuine complexity. Some of the dolphins at facilities like this have been there for many years and may not be releasable. What do you do with an animal that was born in captivity and has never hunted for itself? These are not easy questions. There's no clean answer. Marina: What I do think is that the science on dolphin cognition and welfare should be driving these conversations — and increasingly, it is. The more we learn about what dolphins actually are, the harder it becomes to justify treating them as entertainment props. But the transition to a world without captive dolphin facilities requires thinking seriously about what happens to the animals who are already there. Marina: This story, for me, is really about a broader reckoning that's happening in our relationship with cetaceans. We fell in love with dolphins in part because of facilities that let us see them up close. And now that love, combined with science, is pushing us to ask whether that kind of encounter is actually good for them. That's not a comfortable question. But it's the right one. Marina: And that brings us to the close of today's episode — and I'll be honest, I always feel a little reluctant to stop when the stories are this rich. Marina: What ties all of today's threads together, I think, is this: cetaceans are not just interesting. They are sophisticated, culturally complex, acoustically extraordinary beings who have been living full, communicative, social lives in the ocean for tens of millions of years — long before our species existed. Female dolphins with social networks sophisticated enough to build reputations. Sperm whales with dialects that evolve across generations. Songs that travel in ways that brush up against the edges of physics. These are not minor details. They are reminders that intelligence, culture, and voice took forms in the ocean that we are only just beginning to appreciate. Marina: This is Deep Voices, brought to you by Ada, Ago Consulting, and Zen Semiconductor. Thank you for supporting the science and the stories that keep this show going. Marina: If today's episode moved you, please subscribe wherever you listen to podcasts — it genuinely makes a difference — and share it with someone who loves the ocean, or who needs to. The show notes for today's episode have links to all the research and reporting we talked about, so check those out if you want to go deeper. And remember: somewhere out there right now, a whale is singing something we don't yet understand. Let's stay curious until we do. See you next time.