Saturday, 26 September 2015

The Dog Family: The Marks of Zorros

When North and South America collided towards the end of the Pliocene epoch a little over two million years ago, dogs were, for the first time, able to cross to the southern continent, a place that had previously been somewhat lacking in large mammalian carnivores. The dogs that crossed over all seem to have been related to wolves, rather than foxes. However, the fox body plan and lifestyle, with its high adaptability, proved so useful that most of the living descendants of these animals look just like foxes.

However, they are not "true" foxes, but rather, wolf-like animals that evolved into creatures that happened to closely resemble the members of the much older lineage that we find on the other continents (red foxes, Arctic foxes, the various kinds that we find in Africa, and so on). Recognising the distinction surprisingly early, some nineteenth century naturalists called them "fox-tailed wolves", and there has been a (largely unsuccessful) move to call the animals "zorros" in English, to distinguish them from the true foxes. That this didn't take off is perhaps due to the fact that "zorro" simply means "fox" in Spanish, and most of the researchers studying the animals are likely to be Spanish speakers... so it's not really a lot of help.

There has also been some argument as to what the scientific name of the group should be. Back in the 1850s, German-born naturalist Hermann Burmeister created two genera to describe the animals: Lycalopex (which means "wolf-fox") and Pseudalopex ("false fox"). It's now agreed that there is no real difference between the two, and we should only use one of the two names, but there has been little consistency in the literature as to which one it should be. Technically, because he came up with it first, Lycalopex should have priority, and it has become more popular over the last five years or so, but the alternative is still slightly more common, and, since I tend to use the IUCN as a tie-breaker in these situations, it's the one I'm going to use here.

But, basically, they're the same thing, and "Lycalopex" will probably become more common with time.

The largest of the South American foxes, and the first to be scientifically described, is the culpeo or Andean fox (Pseudalopex culpaeus). This is about the same size as the familiar red fox of the Northern Hemisphere, which is itself the largest of the true foxes, but is, in other respects, a fairly typical representative of the physical appearance of the South American species. It has the bushy tail that distinguishes most foxes, and a snout that, while narrower than one would expect for most "wolf-like" canids, is, perhaps not quite as much so as is typical of true foxes. The coat colour varies a little, but is generally greyish over the back and flanks and tawny or tan over the rest of the body.

Note: some more recent studies have suggested that
Darwin's fox may actually be closest to the Sechuran fox
Culpeos live in western South America, and, as their alternative name suggests, primarily in and around the Andes mountain chain. Other than that preference for a relatively high altitude, they seem to inhabit almost every food-bearing habitat available, from damp equatorial jungles to hot desert margins and the chilly southern wastelands. The further south they are, the less likely they are to venture into the higher peaks, but near the equator they may be found as high as 2500 metres (8300 feet) above sea level.

Perhaps due to their larger size, they are also the most carnivorous of the South American foxes, and, while this mainly means things like rabbits and large rodents, they will attack domestic livestock such as sheep, and wild hoofed animals such as guanacos (a relative of the llama). On the other hand, being foxes, they are far from pure carnivores, and will also eat a fair amount of fruit, especially when game is difficult to acquire. Indeed, they may even act as effective seed dispersers for Peruvian pepper, something that's arguably a bit of a problem in those parts of their range where the plant has been introduced, rather than growing wild.

Although there have been some reports of pairs of males sharing an area, like true foxes, they are mostly solitary animals, avoiding one another outside the breeding season. They seem to be almost entirely nocturnal, and, while there has been some suggestion that this is largely to avoid humans, even where they are legally protected, they still seem to be more active at night than during the day. They mate in the spring, giving birth to a litter of three to eight pups around eight weeks later.

Sechuran fox
If the culpeo is the largest of the South American foxes, the smallest is the Sechuran fox (Pseudalopex sechurae) of the coastal Sechura Desert of Peru. In truth, it isn't that much smaller in its general dimensions, although it's much slimmer build makes it a far lighter animal. Compared with many other foxes, we don't know a huge amount about it.

Clearly, Sechuran foxes prefer dry habitats, since that's where they live, and that seems to vary from thorny woodland to both desert and beach-front sand dunes. They also seem to prefer eating meat, but rarely get the opportunity to do so, subsisting mainly on seed pods and insects. Like many African foxes, they do not need to drink, obtaining the minimal amounts of water they need from their food. So far as we can tell, they appear to be solitary and nocturnal.

Only two species of South American fox live entirely east of the Andes. One of these is the hoary fox (Pseudalopex vetulus) of southern Brazil. This inhabits the cerrado region, the relatively open savannah habitat that lies between the Amazon and Atlantic Forests, and, while we know little of its detailed preferences, it seems to avoid dense woodland and swamp. The great bulk of their diet consists of insects, especially termites. Although they also eat a fair amount of fruit, and will eat meat or carrion if they can get it, the latter is apparently a very small part of their diet, and their jaws are not particularly strong.

Compared with other South American foxes, they may be more inclined to travel in pairs, with mated couples spending as much as a third of their time together. Males have been reported to escort their older cubs on foraging expeditions, even once the female has begun to lose interest in them as they age; this may be partly because carrying food back to the den is rather wasted effort when you're not eating much that's bigger than a termite.

Further south, in the southern tip of Brazil, and in Uruguay, Paraguay, and across northern and central Argentina, we find the pampas fox (Pseudalopex gymnocercus). As its name implies, this inhabits the pampas grasslands that lie south of the main forested regions of the continent, although it is also at home in relatively forested environments and in agricultural land. Pampas foxes are amongst the most generalist of the South American species, eating just about anything that's small enough, and changing their diet to match whatever happens to be available at the time. (On the down side, this does mean that they are enough of a threat to livestock to be worth hunting - but they seem to be common enough that this hasn't had much effect on their overall population).

South American grey fox
Compared with their hoary counterparts, pampas foxes also show more typical habits when it comes to their general lifestyle. Notably, they are much more solitary - even mated pairs spending only about a tenth of their time together. On the other hand, they do bring food home for their cubs, since the bigger bits are likely to be worth the trouble. Where hoary foxes often sleep for the day in rocky ravines and the like, the pampas species is more likely to use burrows - albeit ones dug by animals such as armadillos, rather than something they have constructed themselves.

Further south still, we come to the South American grey fox (Pseudalopex griseus), inhabiting central and southern Argentina and Chile, and even successfully introduced to the main island of Tierra del Fuego off the southernmost tip of the continent. Although it is smaller than the pampas fox, and prefers colder climates, the two species are remarkably similar. Both inhabit a mix of forest and relatively open grassland - the cold steppes of Patagonia in the case of the more southerly species - and both are highly omnivorous, eating whatever they can get. Likewise, they are both nocturnal and solitary, although that tends to be true of foxes in general, and so is rather less meaningful.

So similar are they, in fact, that there is some doubt that they are really separate species at all. The largest and most recent study, in 2013, concluded that the two species gradually merge into one another as you cross the putative boundary between their ranges. In the absence of detailed genetic evidence showing whether or not they interbreed, this would imply that they are, most likely, different subspecies of the same creature. Specifically, since it was named first, it would be the pampas fox that wins out, and gets to keep its scientific name. This can be compared with the culpeo, which also inhabits some of the same area as the South American grey fox, but is clearly both physically and behaviourally distinct (e.g. eating more meat) where the two are found together.

It had long been thought, however, that one subspecies of South American grey fox was found only on Chiloé Island, just off the coast of Chile. First discovered by Charles Darwin in 1834, these foxes were a bit weird, looking rather different than their mainland kin, presumably as a result of their long isolation. But then, in 1990, a small population were found hiding in the Nahuelbuta National Park on the mainland... which meant that their odd appearance had nothing to do with their island life. Genetic testing followed, and it turned out that they were actually a completely different species: Darwin's fox (Pseudalopex fulvipes).

Darwin's fox
Darwin's foxes are small, an effect enhanced by their unusually short legs, and they also have much darker fur than any other South American fox. Although we now know that they don't just live on the island, and we've found even more hidden populations nearby just in the last two to three years, the area that they inhabit is still a very small one. In particular, they only inhabit forests, often hiding particularly deep inside them (which may explain why the mainland populations proved so hard to discover), which limits even those parts of the island that are available to them.

While they'll eat almost anything, in practice, their diet is limited by what is around them. On the mainland, this often means rodents, and, given the chance, they do seem to prefer eating meat. But on the island, where the greatest numbers of them are found, such meat is in short supply, and they have been reported to dine mainly on insects during the spring and summer, and on almost nothing but fruit in the autumn.

They don't appear to be territorial, possibly because they can't afford to be, and are often found close together even outside the breeding season. They may also be less nocturnal than other foxes, perhaps precisely so that they can avoid them, giving them a chance to eat slightly different prey and so survive together in the same area. The little we know of their breeding suggests the use of rocky dens or tree cavities to rear pups, and litters of only two or three at a time.

The total population is estimated to number only around 250, almost all of them on Chiloé Island, and despite official protection for the species, this figure is thought to be declining. This makes Darwin's fox the single most critically endangered of all modern canid species (barring one that's already extinct, which I'll get to in a later post). In addition to the usual problems of loss of habitat and illegal poaching, perhaps the biggest threat is simply the presence of dogs - not so much because they attack the foxes (although they do) but because they carry canine diseases that the small, genetically homogeneous, populations of foxes are ill-equipped to handle.

That there might soon be one less species of fox in the world is a depressing note to end on, although we are at least doing our best to ensure that it doesn't happen. But, in fact, there are two species of fox that I have passed over so far in this survey, and one of them is also an inhabitant of South America...

[Photos by Brian Ralphs, Mike Weedon, "Piker", and Fernando Bórquez Bórquez. Cladogram adapted from Lindblad-Toh et al, 2005 and Bardeleben et al, 2005.]


  1. "pairs of males sharing an area"

    That, I imagine, should say "pairs of mates ..."?

    1. No; I would guess that they were brothers from the same litter.