Episode 5: The zombie mice of Marion Island

Mice on the sub-antarctic Marion Island are out for blood, and they're feasting, zombie-style, on living, immature albatrosses.

Mice on the sub-antarctic Marion Island are out for blood, and they're feasting, zombie-style, on living, immature albatrosses. The tiny mammals are turning out to be a very big threat to these giant seabirds. Photographer Thomas Peshak says it was worse than watching the first four seasons of The Walking Dead.


TOMAS PESCHAK (PHOTOGRAPHER): I’ve watched every single season of “The Walking Dead” and this is rougher than any one of those episodes. It’s a horror show, basically. Zombie-mouse apocalypse with mice and albatrosses.

PETER GWIN (HOST, OVERHEARD AT NATIONAL GEOGRAPHIC): In between assignments in South Africa and South America, photographer Tom Peschak stopped by the Nat Geo studio. And he told us a story that made us stop in our tracks.

PESCHAK: Imagine you are on a sub-Antarctic volcano. It's an island in the middle of the Southern Ocean thousands of miles from anywhere. One of the most remote islands in the world and one of the least visited as well.

GWIN: Tom came to this apparently peaceful island to search for the many species of seabirds that live there and the strange horror that afflicts them.

PESCHAK: All of a sudden in this landscape of black and green and gray there is this red that pops out at you all of a sudden. And you’re just going, “Well, what is that?” You come around this boulder and you are literally looking at a bird that has been scalped.

The entire back of its head and the entire neck has been eaten away. And that's how you find the gruesome evidence of one of the most critical conservation crises that are facing seabirds.



GWIN: I’m Peter Gwin and this is Overheard at National Geographic. I’m an editor and writer for the magazine and this week I have a story for you. It’s about a remote island that’s been overrun by flesh-eating zombie mice. And there’s just one hope for fighting back.

[music ends]

GWIN: We’ll get back to zombie mice in a minute, but first there are a few things you need to know about seabirds. And look, I know what you might be thinking:

PESCHAK: Most people don't care about seabirds. You know, most people think that seabird behavior largely consists of stealing your french fries at the beach and then pooping on your car in the car park.

GWIN: For what it’s worth, seabirds don’t really care about you either. The birds that Tom photographs don’t live anywhere near people. They spend their days hunting for food over thousands of miles of open ocean. And when they’re done, they nest far away from the windshields and finger foods of civilization. And hey, maybe you would too if you had what they had. See, one of the great things about being a seabird is that you get your own private honeymoon island.

PETER RYAN (PROFESSOR): No bird has managed to get over the trick of laying eggs.

GWIN: This is Peter Ryan, a professor at the University of Cape Town. He studies the birds that nest on these islands.

RYAN: The reason why they're breeding on these little remote specks of land in the middle of the ocean is that they are safe havens for them.

GWIN: The particular island that our photographer Tom visited is called Marion, and it’s a halcyon paradise for birds. It’s just 100 square miles, but it’s packed with 28 species of seabirds—scrambling over rocky beaches and screaming out for mates.

[bird noise]

Among those are four species of albatross. They’re enormous birds; the largest of the four has a 10-foot wingspan. It’s called “the wandering albatross” and about a fourth of the world’s population nests on this island. They’re here because Marion is surrounded by a twelve-hundred-mile moat. The island is like a fortress. One that’s secure enough for the albatross to leave their babies unattended in public.

PESCHAK: And they have to leave their young for days and weeks at a time while they while both parents out looking for food. There's no trees to build a nest in. I mean they are nesting on the ground. They are incredibly vulnerable.

GWIN: But vulnerable to whom? This is an island inhabited almost exclusively by birds and insects.

PESCHAK: So during the day they're pretty safe. But then when night falls the mice become active.


[ominous music]

GWIN: Rodents have followed humanity like a shadow. Like cockroaches or pigeons, they eat the food that we throw away and take shelter in our walls. No one meant to bring mice to Marion Island, and no one knows exactly when they arrived. But one day in the early 1800’s, the first few mice landed on Marion with a group of seal hunters. And when the hunters left, those mice stayed behind and started a colony.

PESCHAK: And for two hundred years they peacefully coexisted with the seabirds. The mice ate insects and seeds and the birds come there to nest. And then beginning in the early 2000's, something began to shift. The winters in Marion are getting warmer. And as these winters are getting warmer, it appears that more and more of the mice are surviving.

RYAN: The warmer and drier the summer, the more mice. But then come winter it turns crap again and the mice just become frantic.

PESCHAK: The island can no longer sustain the mouse population.

RYAN: You've got—million mice frantically looking for foraging opportunities.

PESCHAK: And the first thing they came across were these seabirds.




MINITER: What's up?

GUTIERREZ: Can we show you something really quick?


[ambient office noise]

GWIN: Our producer Brian was shocked when he saw the mouse-attack pictures for the first time and he wanted to recreate that experience for a few of us. So we huddled around his computer to take a look.

GUTIERREZ: So what you do is you go to zombie-mouse-dot-org.


MINITER: Oh man.

JACOB PINTER (PRODUCER): It's like—is the whole back of its head, like, open...?

MINITER: It looks like everything is peeled off.

PINTER: ...or missing?


PINTER: Oh God, it looks like a “Saw” movie.

MINITER: How methodical. And you know what? The interesting thing here is the bird is seemingly unperturbed by this whole thing. He's just—I mean has—has the mouse eaten his motor functions? Oh my gosh, there's a second mouse all up in his feathers.

GWIN: It’s true. the birds don’t seem to mind that the mice are slowly eating them from the top down.

RYAN: Yeah, I think at least initially they do. But they just become fatigued by the whole process. During the day all the healthy chicks are standing up and they're flapping their wings and preparing their wing muscles for when they make that first momentous flight out to sea. And you can pick up the guys who are who are being attacked by mice because they're not standing up and they're not flapping; they're just crashed on their nests. And then if you go into the colony at night, the whole situation is reversed. All the happy birds are lying there happily sleeping with their heads tucked away and the guys who are being attacked are standing up so the mice can't get on them.

But slowly through the night I think the poor birds just get fatigued and by three, four o'clock in the morning they lie down. And as soon as they lie down, the mice are on them. And you know two or three nights of that and they’re just exhausted and they just, they just give up. They don't respond.

GWIN: These attacks are particularly gruesome because on Marion, the mice start with the head.

RYAN: We call it scalping and we think that the reason why they targeted the head was because that was the easy place to attack these big fully feathered chicks. None of the video footage has really seen any sort of attempt by the adults to do anything about it. They've certainly got the equipment to kill a mouse. I mean if you put your finger too close to an albatross and it decides to take a bite, you'll know all about it. And they would definitely kill a mouse if they bit them. But they just don't see them as a threat.

GWIN: Evolution happens slowly. And Albatross parents haven’t been around mice long enough to develop a mouse-killing instinct. Their chicks do have one weapon— specialized to fend off other birds on the island: hot stomach oil.

RYAN: And this oil—if it gets onto the plumage of the predatory birds—gives them a really tough time because it disrupts the waterproofing of the feathers and makes basically a big sticky mess that they can't get rid of. But of course, the mice don't really care about that kind of thing. If they puke hot oil on them they'll just lap it up and think it's great.

GWIN: In short, the albatross don’t have the knowledge or the will to take care of the mice themselves. So you might think it makes sense to bring in a specialist. One with mouse-hunting instincts. The Rick Grimes of zombie mice. So—what about cats?


GWIN: Well, long before the mice started attacking the seabirds—back in the 1940’s—a few scientists set up a weather station on Marion and they noticed mice getting into their food.

RYAN: In order to kind of keep the mice from being a problem on the little weather station, they took a couple of cats down. And of course, that's not a very good idea, as we know these days.

GWIN: You can probably guess where this is going.

RYAN: Cats are very non, non-selective. They thought, "Wow, this is paradise. Look at all these stupid birds that have never seen a cat before. You know?"

GWIN: The fight-fire-with-feline approach backfired miserably. Over the next three decades, those five cats multiplied, expanding far beyond the weather station. And they moved on from mice to become a hungry, bird-hunting horde.

RYAN: It was estimated there were about 2000 cats on Marion. And those 2000 cats were killing an estimated 450,000 seabirds per year.

GWIN: It turns out that a honeymoon island for seabirds is an open buffet for house cats. They were driving the island’s birds to extinction. Something had to be done. And so the project to get rid of cats on Marion Island began.


GWIN: The first thing they tried was introducing a deadly cat virus to the island. The disease killed thousands of cats, but they began to develop an immunity, and were soon perfectly capable of bouncing back. So those last cats had to be exterminated individually.

PESCHAK: It took the conservationists years of shooting and eradicating cats to get rid of the cats that they introduced to get rid of the mice in the first place.

GWIN: Doing anything on an island like Marion is tough. At a latitude of 47 degrees south, it’s right in the middle of “The Roaring Forties”—a belt of terrible weather that encircles Antarctica.

PESCHAK: Back-to-back low-pressure systems just plow into this island. This is a tough place to even just be in summer. Now imagine you were living in a tent and you're trying to hunt cats at night with a spotlight.

GWIN: Despite those challenges, the 14-year project was successful and Marion was pronounced cat-free in 1991. But in the background the mouse population was slowly building. And by 2015 they were scalping seabirds with gusto. But hunting mice will be much harder than hunting cats.

PESCHAK: You cannot go out and individually trap hundreds of thousands of mice that have literally spread across the entire island. Luckily there’s hope. You know the technology exists to eradicate mice—even from an island as wild as Marion.

GWIN: And what is this technology?

PESCHAK: Well, it sounds really easy because all you have to do is blanket the entire island with poisoned mouse bait.

GWIN: Oh. is that all? I guess we can pack up and go home now. But it’s obviously not going to be that easy.

HOLLY JONES (PROFESSOR): Let me preface this by saying there's no silver bullet in conservation. But if there was one, invasive mammal eradication on islands would be it.

GWIN: Holly Jones is a National Geographic explorer and professor at Northern Illinois University. She studies remote islands before and after big projects like this. And she knows exactly how complicated it’s going to be.

JONES: Okay. So we have had about twelve hundred attempts at invasive-mammal eradication on islands.

GWIN: And these eradications are generally pretty effective

JONES: So the success rate is around 85 percent.


GWIN: Marion Island is part of South Africa, and recently their government decided to try and kill the mice. All that experience working with smaller islands has taught us that poison is the only way to effectively remove them. There are just too many mice to hunt individually and the terrain is too chaotic to lay traps. But even though it’s the easiest option, it definitely won’t be easy.

PESCHAK: This is an island with mountains and ridges and valleys and lava fields and caves and now you have to go at the beginning of winter.

GWIN: By spreading the bait in winter, they can be sure that the mice are hungry

and more willing to eat the poison. But that horrible winter weather makes things hard because the best way to spread the bait is by helicopter.

PESCHAK: So now they have to get an icebreaker with two helicopters to this island at the beginning of the winter in the Southern Ocean. Now you actually have to fly these helicopters. And Marion Island is one of the toughest places in the world to fly.

GWIN: There might only be two to three hours each day when the pilots are able to effectively spread the poison. And when they do, they must fly very carefully; each square inch of the island must be covered.

PESCHAK: Because if they leave one patch, those mice are going to survive. And they may have killed everything, but those mice are going to reinvade everywhere else. So you have to do it either all at once, or not bother at all.

GWIN: If anything, Tom is underselling how difficult this project will be. The island needs to be coated in poison twice to get any baby mice who weren’t eating solid food during the first round.

The entire project could take months if you build in the time it takes to set up and wait for ideal weather. That whole time, the team on the ground will have to keep several hundred tons of bait dry and mildew-free. And they have to do all of this while protecting the island ecosystem they’re there to rescue in the first place.

JONES: Yeah, so seabirds don't eat bait because they eat fish and other stuff from the ocean. So they're usually pretty good. What tend not to be pretty good are land birds. So this bait is grain based. And so if there's a land bird who's interested in grain based-type stuff then they can eat it.

The other thing is that predatory birds—they could eat the poisoned mice or rats and then die.

GWIN: The conservationists will do everything they can to prevent that from happening: use poison that quickly decomposes, dye the bait green so it’s unappetizing to birds, they may even temporarily relocate some birds to other islands. But none of these precautions are a guarantee of safety.

JONES: If you have a few birds that eat the bait and die, the rest of the birds are gonna go on and they're gonna reproduce and their young isn't gonna get eaten anymore. And so their populations often flourish even if they take a bit of a hit during the eradication process.

GWIN: Jones knows this because she’s had first-hand experience on one of these islands.

JONES: Yeah I've been to—to one. After the Anacapa Island rat eradication.

GWIN: Here’s what that trip was like:

JONES: Some of my least favorite days on islands. So it's, it's great on the one hand because you know that the birds and other animals that you were trying to save are gonna do way better. But at the same time it's never—it's never fun to collect carcasses of animals ever. Right?


JONES: But what I really love is then coming back say a few months or years later and seeing the just huge rebound. Like the rebound happens really fast. In the case of the Anacapa Island rat eradication. Birds stopped just being limited to sea caves and they started sort of nesting in other places. And birds that had never even been documented nesting on the island started nesting on the islands.

GWIN: As people, we have the ability to save an entire island of unique birds. It’s a chance to set right one of the many environmental mistakes humans have made throughout history.

JONES: The mice didn't get there on their own. And so the question is: as sentient beings who know that we brought this problem to islands, do we have an obligation to remove that problem?

GWIN: Of course, removing one problem can cause problems of its own. And we can’t always anticipate them. Just like we couldn’t have foreseen the zombie-mouse apocalypse.

PESCHAK: And what scares the crap out of me is that this introduction happened 200 years ago. Two hundred years. And only now are we seeing the consequences of that accidental introduction.

GWIN: What mistakes are we making now that will lie dormant, waiting to greet us in another part of the world two hundred years from today?


GWIN: If you’d like to see some of Tom’s photographs of the zombie mouse apocalypse—beware they’re very disturbing—take a look at his website. We have a link in our show notes. And if you liked this episode, subscribe to Overheard at National Geographic and leave us a review.


Overheard at National Geographic is produced by Brian Gutierrez, Emily Ochsenschlager, Kristen Clark, Robin Miniter, and Jacob Pinter. Our editors are Casey Miner and Ibby Caputo. Hansdale Hsu composed our theme music and engineers our episodes, with additional help from Nick Anderson, Devin Ocampo, and Jerry Busher. Special thanks to: Pineapple Street Media, Peter Medlin and Rasmus Bitsch. This podcast is a production of National Geographic Partners.

Susan Goldberg is our editorial director. I’m your host, Peter Gwin. Thanks for listening, and see y’all next week.