When Pigs Fly, Island Foxes Die

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Island fox Urocyon littoralis
Island fox, Urocyon littoralis
Photo courtesy Pacific Southwest Region USFWS from Sacramento, US, CC BY 2.0 , via Wikimedia Commons

If you’ve ever thought to yourself, “The world needs cuter foxes… I mean foxes are cute, but if they were even cuter, that’d be even better,” then the island fox may be for you. Also known by Latin nerds as Urocyon littoralis, the island fox is not only adorable, it’s also the subject of a pretty amazing tale of tragedy and recovery. From their very origins to their current survival, they are perhaps unique among wildlife in that their fate seems to have been constantly intertwined with humans since the dawn of their species. Luckily, their tale is not over yet, and so far, the island fox has proven more resilient than anybody expected.

Off the coast of southern California in the United States, there’s a loose group of eight islands known as the Channel Islands. They’re divided in to two groups, the northern islands and the southern islands. Six of those eight islands are home to one of the world’s smallest and cutest canid species, the island fox, which is endemic to those islands, meaning that they’re found nowhere else in the world.

Now, foxy fans out there are saying to themselves, “Hang on, fennec foxes are the smallest and cutest species of canid in the world, everyone knows that!” To which I say, “Shut up, that’s not even fair, fennecs are obviously not real animals but rather creatures from a fantasy anime cartoon brought to life by the wish of a dying child, so they don’t really count.” (Look at a picture of a fennec fox and you’ll see what I mean, they’re ridiculous).

Swipe right for adorbs

But look, this isn’t a fox rating blog, so let’s stay focused on the island fox. The very existence of these guys is pretty fascinating in itself. There is absolutely no doubt that they are directly descended from the grey fox, a much more common species found throughout much of North America. They are also absolutely considered a separate species. For one, they’re dramatically smaller. Island foxes are the size of a cat, and not a big cat either. Not like a Maine Coon. They’re the size of that little stray cat you took in who had obviously never had a decent meal in their life. They also have different behavior from grey foxes, and different breeding habits. But for all that, they’re an extremely young species in evolutionary terms. Carbon dating from the oldest remains discovered on the Channel Islands, combined with genetic analysis, suggest that the island fox split off from the grey fox only 7000 years ago. That’s basically yesterday as far as evolution is concerned, and by itself that’s kind of fascinating.

Island foxes are pretty clearly the result of some grey foxes somehow winding up on these islands and being cut off from the rest of the population, after which they pursued their own evolutionary path until they no longer could really be considered grey foxes. There’s no dispute about this, and in itself, that’s not unusual… islands often have their own special endemic species that are descendants of more common species from the mainland. What’s interesting, though, is the timing. 7000 years ago, human beings were wandering around all over California, and they even lived on the Channel Islands.

Island fox, Urocyon littoralis, licking their chops
Photo courtesy Pacific Southwest Region USFWS from Sacramento, US, CC BY 2.0 , via Wikimedia Commons (cropped original)

Normally, when a critter that can’t fly or swim well ends up on an island like this, you figure it’s the result of an extraordinary event, like a couple of individuals riding a log or a mass of floating vegetation from the mainland out to the island by sheer chance. It’s compared to winning the lottery… it’s super unlikely, as it seems unlikely for animals to end up adrift like this at all, and even more unlikely that they happen to make it to an island before they die of thirst or starvation. But as long as it’s technically possible, over thousands or even hundreds of thousands of years, someone’s bound to hit the lottery sooner or later. And… that might still be what happened. But the fact that humans already lived on these islands means that that theory isn’t the most likely one. It’s quite possible that one of the local native tribes, the Chumash people, captured or even tamed grey foxes and brought them over from the mainland. It also turns out that the Chumash seemed to really love foxes… they considered them to be sacred, depicted them in artwork, and even seem to have even given some island foxes ceremonial burials. And the bonus is, we are pretty sure that island foxes originated in the northern island group, and that the Chumash took them to the southern islands. So, the sure bet seems to be human intervention from the get-go, not the floating log lottery. Although, we don’t know for sure.

All of which means, these little guys probably developed into their own unique species because humans liked them so much, that they introduced them to a new environment where they could flourish. Think about that for a moment. If true, then humans accidentally created an entirely new species, just by moving some individuals from one place to another. That is wild, and I’m not sure if there’s any other species that can make quite the same claim. At the very least it’s remarkably rare. So, the origin of these dwarf foxes is pretty unique in all of biology.

Eagles and piggies and foxes, oh my

So that’s the beginning of the island fox story. Fast forward to modern times. Well, relatively modern. For the youngs out there, this part will still seem like ancient history, long before the age of Tik Tok dances and Playstation 5 scalpers. It all starts with DDT. Remember DDT? Ah, the good old days, when we used to spray poison all over the country, and it killed all the birds, because we didn’t like getting bit by mosquitos at our church picnics. The story of DDT is a whole ‘nother thing, but for now you just need to know that part of the problem with it was that it was an insecticide, used back in the ’50s and 60’s, that accidentally got in to a number of different species of birds. While it didn’t generally kill them, it did make the shells of their eggs thin and fragile. So fragile that birds were breaking their own eggs just from sitting on them in the nest. DDT caused a lot of problems, but most famously it was almost single-handedly responsible for bringing the American bald eagle to the brink of extinction. Bald eagles hadn’t been doing too well even before DDT, and losing the ability to reliably rear young just about did them in.

So, bald eagles had always lived and bred on the Channel Islands. While baldies will sort of eat any meat they can get, they prefer sushi. They spend most of their time hunting fish and seabirds, and only take guys like island foxes when it’s easy and convenient. So, while they might occasionally eat a young fox that gets caught out in the open, they didn’t have a real impact on their populations. That means you might not expect it to matter much to the foxes when DDT wiped out the local population of bald eagles. And maybe it wouldn’t have, but DDT wasn’t the only fuckery that modern humans got up to on these islands. There had also been failed attempts at ranching on them, and when people eventually gave up trying to raise goats and pigs there, some folks just turned their livestock loose. Those animals sustained their own breeding populations, which wasn’t a good thing because they destroyed native plant species and competed with native herbivores. But, that still wasn’t enough to drive the island fox to the brink of extinction… the foxes are omnivores and eat a mix of insects, rodents, fruit and other vegetation, so they can be flexible when their food supply changes.

two bald eagle chicks in the nest, staring directly at camera
These two bald eagle chicks would like to know if that DDT shit was YOUR idea

But, in what is an amazing example of the unexpected interactions that can happen in ecology, the presence of feral pigs on the Channel Islands, plus the local extermination of bald eagles, combined to bring about the island fox’s downfall. Because it set the stage for an outsider to step in: the golden eagle. It turns out, golden eagles and bald eagles don’t play well together. Baldies just don’t tolerate them and aggressively drive them away. So, as long as bald eagles lived on the islands, golden eagles would sometimes come around for a visit, but they never stayed long and never bred there. Once the local bald eagles died out, though, there was nothing stopping golden eagles from moving in and taking their place. They weren’t as badly affected by DDT and their populations never crashed as dramatically as the bald eagle’s did. And the thing is, golden eagles like to hunt mammals, not fish.

Now… this still normally wouldn’t have been a terrible thing for the island foxes. While golden eagles will eat island foxes, the foxes are small and there never were many to begin with on the islands. They were also, historically, the largest animals on the island, so there wouldn’t have been a whole lot else for the eagles to eat. Normally, the golden eagles would have knocked their population down some, but the foxes just wouldn’t have been able to provide enough food to keep the golden eagles there year round… individuals might stick around for a bit, eat a few foxes, and then leave for better hunting on the mainland.

But the pigs changed everything. Golden eagles, it turns out, love pork. Young pigs are the perfect size for them, and there were plenty of them on the islands thanks to humans. So, when the bald eagles died out and the golden eagles moved in, they had a feast on their hands… or talons. Whatever. Point is, with the pigs, there now was enough food to convince the goldens to stick around and raise families. This was something they had never done before. But they didn’t just eat pigs, of course. If they had, that would have been fine. But no. They also ate those cute little island foxes every chance they got.

Trash pandas ruining everything

The problem was, adult foxes are a perfectly good meal for an eagle, but adult pigs aren’t, they’re too big. So what happened was, the golden eagles would eat all the foxes, cubs and adults. Their populations would crash. But the adult pigs survived and kept on breeding and pumping out delicious meals for the eagles, and enough of the piglets grew up to keep things going. If the eagles had just relied on the foxes for food, their populations would have crashed when the foxes did, and that would give the foxes a chance to build their numbers back up a bit. It would have created a boom and bust cycle, which we see in other species where there’s one main prey species for a predator. But with the pigs as an alternate food source, the eagle populations stayed pretty stable. They ate foxes whenever they could, and otherwise relied on the pigs for a steady food supply. The foxes never got a break.

Feral pig in tall grass
You, piggo. I blame you. You’re the one.
Photo courtesy of California Dept of Fish and Wildlife, Sacramento, CA, USA, CC BY 2.0 , via Wikimedia Commons

By the late 1990’s, it was obvious that island foxes were in a bad way. And biologists were pretty sure they knew why. They had actually been observing the golden eagles eating foxes, and they were finding fox remains in eagle nests. The only good thing was, the eagles weren’t as big of a problem in the southern group of islands. The biggest of the southern Channel Islands, Santa Catalina Island, still had people living on it along with the foxes, and the foxes seemed to adjust pretty well to their presence. While the Santa Catalina foxes are considered a different sub-species from the foxes on the northern islands, they were still a fairly stable reserve of island foxes, so at least the entire species wouldn’t go extinct if the northern populations died out. Until, that is, a drunken raccoon showed up.

Well, okay. Not drunk, but it probably was acting strange. The story goes that a raccoon hitched a ride on a ship from the mainland to Santa Catalina, and this raccoon was sick with distemper, a viral disease more commonly associated with dogs. In raccoons, along with other symptoms, distemper causes them to behave strangely and erratically, including stumbling around randomly during the daytime and bumping in to things. Like they’re drunk. It’d almost be kind of cute if it weren’t a death sentence for them. And the island foxes apparently had no defenses against it, because all of the sudden, distemper was spreading through the Santa Catalina foxes like wildfire. In one year, it had nearly wiped them all out. So, between golden eagles and distemper, by 1999, the total population of island foxes had gone from several thousand to just a couple hundred. Populations on two of the islands had gone down to just 15 individuals. That could very easily have been the beginning of the end for the island fox.

Setting things back to normal

Luckily, though, the island fox had plenty of friends among us humans, and an urgent recovery effort was begun in the year 2000. Researchers had a pretty good understanding of what had gone wrong and what a complicated set of circumstances had led to it. So they knew that to reverse the damage would take a coordinated, multi-pronged approach. The first step was to capture as many foxes as they reasonably could from each island, and attempt to breed them in captivity while keeping the subspecies from each of the islands separate and still trying to minimize inbreeding. This step was crucial. Dealing with the ecological conditions that brought the populations down was going to take time, and there was no guarantee the island fox would survive long enough to see that happen without captive breeding.

Keeping and breeding wild animals in captivity is never a sure thing. Some animals are hard to just keep alive in captivity, and many species are difficult or impossible to breed in captivity. They’re so sensitive to their environments that we just can’t provide an artificial environment that’s good enough for them. Fortunately, island foxes turned out to be a piece of cake to keep and breed in captivity. Maybe the Chumash did tame them, maybe that’s partly why it was so easy to keep their descendants. Regardless, it was good news for the island fox. Meanwhile, the pig and eagle food web had to be dismantled. And this actually turned out to be harder than you might expect.

Golden eagle in snow feeding on a carcass
And this would be why golden eagles were such a problem in the Channel Islands
Photo by Jarkko Järvinen, CC BY-SA 2.0 , via Wikimedia Commons

First off, there was the thorny issue of removing the golden eagles from the Channel Islands. You see, they couldn’t just shoot the eagles. Golden eagles are not only protected by U.S. federal laws such as the Migratory Bird Treaty Act, they actually have their own special law that protects just them as well as bald eagles. The Bald and Golden Eagle Protection Act meant that biologists couldn’t just up and kill the golden eagles in the islands. It didn’t matter that the golden eagles were doing okay on the mainland while the island foxes were on the brink of extinction. The law isn’t very flexible. So, we had one protected species standing in the way of the recovery of another. The compromise was to trap and relocate the birds, a process that was much more time consuming, difficult, and expensive than just shooting them would have been. And there was no guarantee that it would work… the eagles might well just make their way back to the islands.

Meanwhile, the feral pigs that plagued the islands had to be dealt with. Even this turned out to be trickier than expected, because the pigs actually had their own advocates. Some animal rights advocates vocally opposed killing the pigs. The United States Humane Society published opinion pieces in the newspapers, arguing that the pigs had as much of a right to live on the islands as the foxes. And you can see their point. If you view a pig as an individual with thoughts and feelings, then it does seem pretty harsh to kill it just because it was in the wrong place at the wrong time. Same goes for the golden eagles, for that matter.

Here, piggy piggy

But the fox biologists had a pretty hard time buying it. These pigs, after all, were domestic animals gone feral. They weren’t a unique species. They weren’t even an unusual breed of pigs. They were just ordinary pigs. For better or for worse, biologists tend to look at problems from a population or species level, not from the point of view of individuals. Pigs as a species weren’t about to go extinct any time soon. The island fox was. The interaction with golden eagles insured that foxes and pigs wouldn’t be able to safely co-exist on the islands. And re-homing the pigs would be even more difficult than moving the eagles. There were a lot more of them, for starters. And even if you could trap them all, you couldn’t just turn them loose somewhere on the mainland… that would just be transferring the problem from one place to another. In the end, the need to reset the ecology of the islands won out over the rights of the pigs to live there. Pigs were eradicated from the northern Channel Islands within a couple of years, along with feral goats, sheep, and even mule deer and elk that had been introduced as game animals. Any remaining golden eagles were deprived of all their favorite foods.

The third big step was to bring back bald eagles. By 2000, DDT had been banned for a while and the waterways baldies depend on for fish were a lot less polluted than they had been in the 1960’s and 70’s. So capturing some bald eagles and releasing them on the islands without harming any populations on the mainland was a lot more feasible than it once would have been. And it worked. Enough of the bald eagles stuck around and started to breed that they kept the golden eagles away. The ecosystem was returning to normal.

Island fox in low vegetation
Pacific Southwest Region USFWS from Sacramento, US, CC BY 2.0 , via Wikimedia Commons

But, the recovery effort didn’t stop there. Though it wasn’t the main factor in the decline of the island fox, the plant communities on the islands had been pretty drastically altered by humans as well. Native plants that the foxes liked to eat had been replaced with non-native species, either by accident or planted intentionally by people who had lived there. A lot of the scrub brush the foxes preferred had been replaced with non-native grasses, and wetlands had been filled in. So, work was done to start removing the exotic plants and to replace the native species that the foxes used as food and cover. The wetlands were dug out and restored. Unlike the mess with the eagles and pigs, restoring the plant community has proved to be much harder… seeds can persist in the soil for years before germinating, and a single plant that’s overlooked can repopulate the whole island. Plus, people still visit the islands and still live on some of them, so they’re going to keep introducing non-native plants, either on purpose or accidentally. It’s likely that the work to restore the native plant community on the Channel Islands will be an ongoing effort for the foreseeable future. But it’s still been pretty successful, and a lot of the original habitat used by island foxes has been restored.

There was still the problem of the distemper virus, of course. There was no way to ensure it was gone from the Channel Islands, and absolutely no way to make sure it wouldn’t return. Especially with people living on the islands and visiting them, along with their dogs who should be, but might not be, vaccinated against the virus. Plus there was always the chance, even likelihood, of another sneaky raccoon showing up. So the captive foxes all got vaccinated, not just for distemper but for rabies as well. And, once the whole situation with the eagles and pigs was sorted out, they started releasing the vaccinated foxes back to their respective islands. The released foxes did so well, that by 2007, the captive breeding program was no longer needed and all the remaining foxes were turned loose. By 2016, the population levels on all the islands were about where they had been historically.

The comeback kits

All in all, the recovery effort was amazingly successful. A lot of things could have gone wrong… the island foxes could have proven difficult to breed in captivity. The golden eagles could have proven difficult to keep out of the islands. The bald eagles might not have become re-established. Enough pigs and goats could have managed to survive to repopulate the islands. And any number of other, unpredictable things could have happened to throw a wrench in the works. But none of that happened. Everything went more or less according to plan. The science was followed and… it all just worked. Nature is inherently unpredictable, and just because in theory ecosystems should work a certain way, doesn’t always mean they actually do. But this time it all worked out. The bald eagles kept the goldens away. The feral animals were successfully eradicated without any surprise reappearances. And when returned to an ecosystem that looked more like the one they had evolved in, the foxes thrived. And it only took about 16 years to achieve all this. No other species has ever declined and then recovered in such a short period of time. It’s remarkable.

Of course, the future isn’t guaranteed for the island fox. Distemper will always remain a threat. On Santa Catalina specifically, humans remain a threat. There’s a couple little towns there, and lots of tourists visit. A couple dozen foxes get hit by cars or killed by dogs each year. It’s not a huge problem, but with only a couple thousand individuals on the island, you want to avoid these sorts of accidents as much as possible.

Island Foxes II: Clone Wars

There’s also the problem of genetics. The island fox was probably never very genetically diverse anyway. Genetic studies indicate they probably originated from just a few or maybe even just two individual grey foxes that colonized the islands. Any more genetic diversity than that is just thanks to whatever random mutations have cropped up in the seven thousand years since then. And while the foxes seemed to be doing fine with such a limited gene pool, the devastating population crash in the ’90s made the genetic situation much more extreme. When a species recovers from such a small population like that, we call that a genetic bottleneck. A species can go in to a bottleneck with a diverse and robust gene pool, and come out of it with a bunch of inbred individuals that all share the same genetic disorders or disadvantages. Sometimes this doesn’t turn out to be that harmful, but other times, they never really recover from it, no matter how big their population gets afterwards. For now, island foxes seem to be okay. In fact, it’s kind of shocking how well they are doing, considering how restricted their genetic diversity is now.

Pair of island foxes, one nuzzling the other's face
They’re not cute. They’re not! You’ll never convince me.

The most extreme example of this potential genetic problem is the San Nicolas subspecies. The foxes on this island now have such a low genetic diversity, that the individuals are all nearly clones of each other. They are possibly the least genetically diverse population of mammals in the world. Their populations have dropped significantly since their initial recovery, down to around 250 animals from around 700 a few years before. On the other hand, research done in the 1980’s before the big crash suggests that the fox population on San Nicolas may have always fluctuated, so only time will tell if this kind of incredible lack of genetic diversity is a problem for that subspecies or not. The fact that they’re surviving at all, with no obvious signs of genetic disorders or the usual issues you see with mammalian inbreeding, is pretty amazing. If a group of humans became that closely related, they’d be like something out of a horror movie, if they managed to survive at all. Island foxes just keep surprising us.

The story of the island fox is one of the more fascinating conservation success stories out there, and a great example of how tinkering with ecosystems can have unexpected results. We nearly wiped out a unique species that we probably created to begin with, despite the fact that we never hurt the animals themselves directly. And that’s why I continue to find biology and ecology fascinating. Everything affects everything else, and while you can study it and model it and create mathematical formulas to describe it, the interactions even between just three or four species can prove to be surprisingly complex and hard to predict.

And now I’m off to capture some fennec foxes and introduce them to some deserted island. It’s a bit of an investment, but if things go according to plan, in just a few thousand years they’ll evolve in to a species that’s so little and cute, it’s gonna make that Baby Yoda guy look fugly.


National Parks Service Island Fox Page
Remarkable Recovery of the Channel Island Fox
The Fates of Channel Island Foxes and Isle Royale Wolves

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