Cheating Little Vixens

The majority of mammal species are either polygynous, where one dominant male mates with multiple females, or promiscuous, where both sexes have multiple partners. However, while monogamy may be less common, it isn't exactly rare, either, with it having evolved several times in widely separated mammalian groups. In some cases, this is what we would term "facultative" monogamy, where animals (often large predators) are sufficiently widely spaced that it's simply difficult for a male to find multiple partners, or, if he can, they live sufficiently far apart that he can't plausibly defend more than one of them from his rivals. In others, monogamy is an essential part of the breeding process, typically because the young are too much effort for one parent to raise alone.

The Crab-Eating Fox That Wasn't

There are many species of "fox" native to South America. I covered all of these in a series on the dog family a few years ago and I noted at the time that they aren't really foxes in the sense of being related to the likes of red, Arctic, and fennec foxes. Instead, we know from both genetic and anatomical studies that they are more closely related to the group that includes wolves, jackals, and coyotes. 

The dog family has its origins in North America and it seems clear that what happened here is that some wolf-relative that happened to look a bit like a fox headed south at some point, where all of its remaining descendants live today. North and South America joined up relatively recently, geologically speaking, so it's likely that the origins of the South American foxes actually lie in the North, already looking somewhat like their modern form before they made the trip.

Miocene (Pt 17): A Diversity of Dogs

Eucyon

As North America dried out in the Late Miocene, and slowly transitioned towards the deserts and open grasslands that became dominant across the central parts of the continent, it wasn't just the herbivores that were forced to adapt. Carnivores may not have been affected so directly, but, if their food source was changing, they had to do so too.

There were two particularly significant changes among the North American mammalian carnivores that took place around this time. One was the extinction of the bear-dogs, a group with a long history on the continent that was, by this time, typified by relatively large animals that would have looked more like bears than dogs (although they were neither). Over in Europe and Asia, the bear-dogs survived for rather longer, although even there they struggled...  but in North America, the changes were too extreme for them to cope with, and they died out as the Late Miocene dawned.

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.

The Dog Family: The Marks of Zorros

Culpeo

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.

The Dog Family: Arctic and Grey Foxes

Arctic fox

The same generalist habits and adaptability that have allowed foxes to colonise the deserts have also allowed them to evolve to suit one of the other great barren ecosystems: the Arctic tundra. Here, where even wolves are not particularly common, we find what else but the Arctic fox (Alopex lagopus)?

Arctic foxes are truly creatures of cold and desolate habitats. In Europe, they are found only in Norway, Iceland, and the coasts of the White and Barent's seas in northern Russia. Indeed, it is one of only two species of land-dwelling mammal native to Iceland - the other is the wood mouse, although there are some human-introduced animals there as well. Elsewhere Arctic foxes are found right round the coasts of the Arctic Ocean, in northern Siberia, in northern and western Alaska, northern Canada and its islands, and even in Greenland. Despite this wide, multi-continental, distribution, most belong to just one subspecies, although those living in Iceland, Greenland, and Svalbard form one or two distinct subspecies between them, and there are also distinct subspecies on the isolated Pribilof and Commander Islands in the Bering Sea.

The Dog Family: Foxes of Africa

Fennec fox

The fact that foxes will eat pretty well anything that's small enough has meant that some species have been able to colonise surprisingly harsh environments. The kit fox, for example, inhabits the desert shrublands of much of the western US, while Blanford's fox lives in the dry hills of the Middle East and south-central Asia. No fox, however, is more desert adapted than the fennec fox (Vulpes zerda) of North Africa.

Fennec foxes (sometimes simply called "fennecs") are also among the most distinctive of foxes. For one thing, they're the smallest wild members of the dog family, with particularly small adults as little as 33 cm (13 inches) in length, plus tail, and weighing just 800 g (28 oz.)  They have pale sandy-and-white fur, which is unusually long and soft - they even have fur on the pads of their feet, to give them some protection from baking hot sand. And, of course, there are the huge ears, quite out of proportion to the rest of the animal, which help to radiate away heat in an animal that would rather not lose too much water by panting.

Fennec foxes live across almost the whole of the Sahara Desert, from the Atlantic coast to the Nile valley. They are not typically found east of the Nile, where the closely related Blanford's foxes are found instead, but there are a few exceptions, and, for example, both species inhabit the Sinai. In fact, fennec foxes actually prefer the open sand dunes of the desert interior, an exceptionally harsh and arid environment.

The Dog Family: Foxes of the American West

Swift fox (in summer coat)

There are six living species of fox native to the North American continent. One of those is the red fox, which is also found through much of Asia and Europe. Three others, including the grey fox of the southern US, are not traditionally considered to belong to the genus Vulpes, and I will be returning to these at a later date. Which leaves two close relatives of the red fox that are unique to the continent. Both, as it happens, live out in the wilds of the American West.

Heading out into the west, the first of these two species we come to is the swift fox (Vulpes velox). The native range of this animal happens to line pretty up well with a series of interstate borders, and it's found from northwestern Texas/eastern New Mexico in the south to western South Dakota/eastern Wyoming in the north.

As one might imagine, given this area, they like flat, wide open short grass prairie, and apparently avoid everything else, although they don't seem to have a great problem with cropland. They are small foxes, standing only about 30 cm (one foot) high, similar in height to a small terrier or a King Charles spaniel, although, due to a slim build, they are also considerably lighter than those dog breeds. During the winter, they have a dark grizzled grey back with tan markings on the flanks and legs, but, aside from the black tip to the tail and the pale belly, the whole animal takes on a browner hue in the summer, when it sheds its thick pelt.

The Dog Family: Foxes of Asia

Blanford's fox

Asia is a large and varied continent, home to no less than seven species of fox, even using the most narrow of definitions for that term. Three of these, the red, Arctic, and Rüppell's foxes, are also widespread on other continents; the red foxes of Japan, for instance, belong to the same species as those found in Britain and North America. Of the four that are (mostly) confined to Asia, I have already covered the corsac fox of the central steppe lands, but three still remain.

Heading east from Europe the first such species we come to is Blanford's fox (Vulpes cana). This is named for William Thomas Blanford, who first described it as a unique species in 1877 while working for the Geological Survey of India. Blanford, who discovered the animal in what is now Pakistan, seems to have been somewhat surprised that he was first European naturalist to notice it. He may have had a point, since it's fairly distinctive.

The Dog Family: Red and Corsac Foxes

Red fox

Most members of the dog family can be described, broadly speaking, as "foxes". The term "fox" no longer has a strict scientific meaning, since it encompasses two separate lines of evolution that aren't directly related to one another. Furthermore, as we'll see in a few month's time, there are some animals within those lineages that really aren't foxes at all, as we'd normally think of the word.

Nonetheless, it's a term that's widely used, and is taken to refer to small to medium-sized canids that have have bushy tails, prominent ears, pointed snouts, moderately long legs, and so on. The archetypal such animal, and the one that most people in the Northern Hemisphere likely think of first when the term "fox" is used without any further qualification, is the red fox (Vulpes vulpes).

The red fox is, in fact, the largest of the "true" foxes (as opposed to those of the second, younger, evolutionary line, which are actually more related to wolves). It is also perhaps the most brightly coloured of all foxes, although there is some variation in the coat colour, with brown, yellowish, and even silvery-grey individuals. None of these match directly to any of the more than forty subspecies that have been identified over the years, although it's likely that many of those represent rather finer hair-splitting than is actually required.