The Dog Family: Bat-eared and Crab-eating Foxes

Bat-eared fox

The species of the dog family can, broadly speaking, be placed into three main subgroups: the wolf-like dogs (including, for example, coyotes), the true foxes (that is, those related to the red fox of the Northern Hemisphere), and the South American, or "false" foxes. However, there are a few species whose placement in the family tree is rather less certain. One of these is the grey fox of the eastern US, but there's another that's so peculiar it was once placed in a subfamily all of its own, as if it weren't really a fox at all.

The bat-eared fox (Otocyon megalotis) lives in eastern and southern Africa, although, interestingly, not in between. They can, for instance, be found in far northern Zambia and Malawi, and in far southern Mozambique, but that's as close as the two populations get. Which, to save you the trouble of getting out a map, is a gap of about 1,000 miles or so. Given their complete lack of contact with one another, it is perhaps unsurprising that the two populations are considered separate subspecies.

Modern genetic analysis has shown that bat-eared foxes probably are real foxes, albeit ones whose ancestors diverged from the line that led to all the other true foxes very early on. It has to be said, though, that that isn't 100% certain, and it's possible that the divergence was so early that they just go at the base of the tree, not closely related to anything.

But what, you might wonder, is so strange about bat-eared foxes that caused us to place them in separate subfamily even before we had any molecular data? Well, actually quite a lot - as foxes go, they're pretty weird. But the crucial factor at the time was the number of teeth that they have. The basic pattern for all placental mammals is that each jaw should have three incisors, one canine tooth, four premolars and three molars on each side. Most living species have lost some of these teeth along the way, leading to the various different patterns we see today; dogs, for instance, generally have two, not three, molars in the lower jaw.

But what doesn't happen, except in dolphins and the like, is that placental mammals get more teeth than their ancestors had. Which is why the fact that bat-eared foxes have four molars in the lower jaw is so peculiar. With three molars in the upper jaw (more than a dog should have, but at least not beyond the maximum that ought to be possible), bat-eared foxes have a total of at least 46 teeth, more than any other land-dwelling placental mammal. Some individuals, in fact, have even more, with up to 50 teeth being reported.

This appears to be due to a mutation somewhere in their ancestry that led to them growing an extra upper first and lower second molar, in the same way that individual humans might sometimes have six fingers... but, in this case, it's a mutation that stuck, and became a hallmark of the species.

To the casual observer, of course, the fact that the fox has more teeth than it has any right to is far from obvious. But what certainly will be obvious are the enormous ears that are the source of both its common and scientific names. (The scientific name means something like "giant-eared ear-dog", somewhat redundantly). Other than that, it's a smallish fox, with a particularly slender body and a distinctive coat pattern of black and grizzled honey-tan. Oh, and getting back to the teeth again, they're remarkably blunt and rounded for a dog, and don't have the usual meat-shearing surfaces on what ought to be the carnassials.

The large ears, blunt teeth, and slender build are all related to the fox's diet, which is also the source of many of its behavioural quirks. Bat-eared foxes feed primarily on termites, and, in particular, on just two species of harvester termite. These termites are found in eastern and southern Africa, although, interestingly, not in between. They can, for instance, be found in far northern Zambia and... do stop me if this is sounding familiar.

To be fair, it's not quite that they eat nothing but termites. They also eat a fair few beetles, for instance, along with some other invertebrates, fruit when it's in season, and even, very occasionally, small vertebrates and eggs. But pretty much everything that the foxes do is shaped by the habits and availability of harvester termites.

They live in grassy plains, open savannah, and scrubland, because that's where the termites are. They're nocturnal in East Africa, because so are the termites there... but in southern Africa, where the termites come out during the day in winter, so do the foxes. They maintain relatively small territories of just one or two square kilometres, because the termites stay put and they don't need to travel far to find them. And they hunt almost entirely by sound, holding their snout close to the ground and their large ears cocked forward to hear termites rustling through the grass.

Like other foxes, the bat-eared species tends to live in mated pairs. However, the partners are remarkably faithful to one another, apparently sharing a deeper and more exclusive pair-bond than is typical of foxes, and with paternity tests showing more fidelity than in any other dog species. While this isn't universally the case, especially in East Africa where some males may travel with two or three breeding females, that it typically is is likely also to do with those termites.

It's one thing for a wolf to bring meat home for his pups, but carrying termites is a bit tricky. Instead, until they're old enough to join in on foraging expeditions, the young really do have nothing much to keep them fed except for their mother's milk. That means that she has to do a lot of foraging herself, even before her pups can follow her about, to be able to produce enough milk, and, in particular, to get enough to drink. Rather than leave the pups alone, she leaves them in the care of their father, who spends much longer caring for and grooming the pups than male foxes normally do. So he'd better make sure they're his.

Sure, if he can father pups by two or more faithful females, that's even better for him, but it's a lot of effort, especially when he has to spend so much of his day looking for termites himself. Which explains why polygyny does happen, but isn't that common.

Communication between the foxes is, despite their excellent hearing, primarily visual, and they aren't particularly noisy animals. Movements of their ears and tails seem to be their favoured way of conveying things to one another, including holding their tail in an unusual (for dogs) bent position when they are frightened or particularly excited. The pair bond is established during the winter, mainly by having quite a lot of sex - up to ten times a day, over the course of several days - and cuddling up to one another afterwards. Litters have anything up to six pups, although two or three is most common, and the young are initially sheltered in an underground den.

Crab-eating fox

In comparison, the crab-eating fox (Cerdocyon thous) of South America is not quite such a peculiar animal. It is undoubtedly related to its neighbours, the zorros or "false" foxes, but not very closely. Indeed, the oldest fossil relatives of the living animal actually come from North America, where they lived before the two continents collided. Both that animal and the ancestors of the zorros must have headed south separately to give rise to the various species we have now.

Physically, the crab-eating fox is unremarkable. It is medium-sized for a fox, with a dull grey pelt, and the usual fox-like features of a bushy tail and pointed snout. It lives very widely across the northern, central and eastern parts of the continent, where it inhabits virtually every habitat available to it, save for the depths of the Amazon Forest and the chilly grasslands of the south. This adaptability means that it does not seem much bothered by logging and the advance of agricultural land, and it even seems happy on the fringes of urban habitats.

Crab-eating foxes do, indeed, eat crabs, although largely because they eat just about anything they can find. The exact mix of their diet varies tremendously across their range, depending on what happens to live where they do. In the mountainous forests of southeastern Brazil, for instance, fruit forms the largest single part of their diet, while in a suburban area in the same general part of the country, they eat almost no fruit at all, feeding primarily on rodents. And, yes, in the forested lowlands around the Orinoco River in Venezuela, close to where the animal was first described, they mainly feed on freshwater crabs.

They live in mated pairs, often accompanied by two or three fully grown, but non-breeding, young. This latter feature is unusual among South American foxes, and male crab-eating foxes in particular seem to remain in contact with their parents after leaving home. Some have even been reported to return to their parents' territory to help look after younger siblings from subsequent litters. Another peculiarity is an unusually low metabolic rate, apparently at least partly because they don't need to put too much effort into finding something that they're willing to eat.

Small-eared dog

The short-eared dog (Atelocynus microtis) has been found to be a close relative of the crab-eating fox by some studies, but not by others, so that its exact position in the dog family tree is not entirely clear. In fact, relatively little is known about it, due to a combination of it living only in the depths of the Amazon jungle, and being quite good at hiding. When they are seen at all, it's during the day, and usually near rivers or swampland - or actually in them, as they seem to do a lot of swimming.

Short-eared dogs are about the size of a large fox, and have the same pointed face and bushy tail we'd expect of foxes, but with short, rounded ears, that we definitely wouldn't. Their colour seems to be quite variable, although a sort of dark grey is apparently most common. They're omnivores, as foxes typically are, although with a strong preference for fish, at least in the places we've seen them. They seem to be quite solitary, not even sticking to mated pairs, and when we do see females with pups, it's in the dry season, so presumably that's when they give birth.

Which is about all we know of this, perhaps the most mysterious of all dogs. It also brings me to the end of the animals that could reasonably be called "foxes". There are, however, four species left in the dog family that I have yet to cover, animals that are neither foxes nor truly wolf-like. To see the first two of those, we don't even have to leave South America...

[Photos by Joanne Goldby and "Giro720", from Wikimedia Commons. Painting by St George Mivart, in the public domain.]