The Catlike Canid

Until the 1990s, no one really knew about island foxes. Sure, a few did; the species had existed on California’s Channel Islands for a while, but they hadn’t been around as long as most other North American wildlife (more on that later). So if you had visited out there, you might have seen one or two. But that’s the only place they live. In fact, they are the most “geographically restricted” of any of the canid (dog-like) species; they only exist on the six largest of California’s eight Channel Islands. And they exist at very small population sizes, no more than 500 to several thousand on any of the islands. They’re also very small, physically; indeed, island foxes are one of the smallest canid species (there are other pretty small fox species: fennec foxes, of the Sahara and Sinai Peninsula, weigh in at 1.5 – 3 pounds).

One reason island foxes are small is that, for many island species, it helps to be small. Resources are basically in short supply on an island, which has limited area and resources compared to the mainland. If you’re smaller, you don’t need as much to eat. So not only are island foxes small, they have smaller territories than other canid species, and also smaller litter sizes, averaging only about two pups per litter. There are other, more dramatic examples of this island syndrome, the tendency of island species to be small. Full-size mammoths made it out to the Channel Islands during the Pleistocene, and evolved into the pygmy mammoth, a species that stood only shoulder-high.

Now, not many species actually make it out to offshore islands, and the Channel Islands have never been attached to the mainland. The Channel Islands are continental islands, meaning they’re fairly close to the nearby continent (in this case 15-50+ miles from mainland California), as opposed to oceanic islands, such as the Hawaiian island chain. Species have primarily arrived at the Channel Islands by flying or swimming, though there are two other ways foxes, which really don’t swim, may have arrived. The first is called rafting: foxes may have floated out to the islands on rafts of vegetation debris when El Nino storms sent surges down nearby rivers and out to sea. This is also called “sweepstakes” dispersal, because of the low probability that it has of occurring.

The other possibility is a more delicious one. It’s possible that native Americans may have brought foxes to the islands. The genetics of the island fox is well known, and the mainland gray fox is their closest ancestor. In fact, the island fox looks like a junior version of the gray fox, being a third smaller than its ancestor. And here’s the thing: there are no island fox fossils older than about 6,000 years, and that’s well within the time frame of human occupation of the islands, which goes back about 13,000 years. So it’s entirely possible that natives brought mainland gray foxes to the islands, and that some evolved, rather rapidly, into the island fox species we know today. Island foxes enjoyed a special relationship with the Chumash and Tonga, native peoples of the islands. Island foxes were never hunted by these natives, and some appear in native burials, as if they occupied a higher status. Plus we know for a fact that native Americans transported island foxes from the northern islands, where they first evolved, to the southern islands. All this may add up to a human-assisted colonization of the islands by foxes. And that serves to bookend this story nicely: humans may have brought foxes to the islands, and now have the opportunity to ensure their persistence into the future.

As it is, island foxes rapidly evolved into the six different subspecies recognized today, one on each island where they occur. They are different enough genetically and physically to justify that distinction. Island foxes are the largest native carnivore on the islands, the undisputed kings of their habitats; there are no other medium to large-size carnivores, such as coyotes, bobcats or mountain lions. Because they were never hunted by humans or other animals, island foxes are less nocturnal than other carnivores, and can be observed during the daytime and at dawn and dusk. While this expanded their opportunities to hunt, mate and otherwise be foxes, it also made them vulnerable to the appearance of a novel predator, as we shall see in our next installment…