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.
As one might expect, they are well adapted to the heat. Fennec foxes start to shiver if the temperature gets much below 23°C (73°F), and temperatures have to exceed 37°C (99°F) before they begin to feel uncomfortable enough to start panting. Although they are certainly happy enough to drink on the rare occasions they come across water, they don't actually need to do so, being able to gain enough water from their food alone. Their kidneys are remarkably efficient, producing urine that can be up to five times more concentrated than that of humans.
On the other hand, it does get very cold in the Sahara at night, and, while their long fur does help protect them from this, it's also one of the main reasons that they need sand dunes - they need something at least moderately soft to burrow into when the sun goes down. In the right sort of soil, fennec fox dens can be extensive, up to 10 metres (30 feet) in length, and often with multiple entrances.
What do they eat out in the desert? They can eat small lizards, desert rodents, and the like, as well burrowing into the ground to access the tubers and roots of the few sizeable plants they come across. But mainly they eat insects, such as grasshoppers and locusts. Here, the large ears show their secondary purpose, giving the animals an acute sense of hearing (it's not just the visible part of the ear that's large, but also the internal anatomy). They can hear small animals moving across the surface of the sand, and even burrowing beneath it, rapidly digging to excavate their prey if necessary. Unusually among foxes, they do not perform the typical four-legged pounce to capture small prey, simply darting straight for it.
They hunt alone, but, this aside, are quite social animals. As with most foxes, they are monogamous, but the offspring of a mated pair can remain with their parents for over a year after they have reached nominal independence, and the dens of neighbours may share connecting tunnels. They greet one another with yaps, barks, or squeaks, depending on the context, and can even purr when they're happy. And, as if all of that isn't cute enough, the adults also play with one another almost as much as the pups do. (In respect of this social life, incidentally, it has been noted that, despite their much smaller size, their brains appear to be just as anatomically complex as those of the largest wild canid, the grey wolf).
They breed between January and February, giving birth to a litter of up to four pups about seven or eight weeks later (compared with nine weeks in the domestic dog). Like all dogs, their mating is marked by a "copulatory tie" that physically prevents the pair from detaching once they've started the act. However, this does last an unusually long time in fennec foxes; two hours is about average, with the maximum adding another 45 minutes or so to that.
For instance, it is an unusually small fox, but not as small as the fennec. It has a sandy-coloured coat, but one that's slightly darker and greyer than the fennec's is. It has large ears, but not quite that large. In other respects, the similarity is stronger; it has fur on the soles of its feet, and it drinks when it can, but doesn't actually have to.
Despite this, the fennec fox was, for a while, thought to be sufficiently unique to be given its own genus, Fennecus. We now know that it's very closely related to Blanford's fox, and so belongs to Vulpes. However, while those two foxes presumably share a single, desert-dwelling ancestor, Rüppell's species turns out to be a close relative of the common red fox, representing an entirely separate evolutionary adaptation. This likely happened later than the Blanford's/fennec origin, when something akin to the red fox first ventured into the southern deserts.
Rüppell's fox has been studied rather less than the fennec fox, likely at least in part because the latter is more extreme, and therefore potentially more interesting. It manages to avoid too much competition with its smaller relative by staying away from the worst parts of the desert, preferring rocky margins, dry river beds, oases, and semi-desert steppe land. Where fennec foxes are not found, however, it does inhabit terrain more associated with that species, such as the sandy interior of Saudi Arabia, and of certain parts of Pakistan.
They eat much the same food, concentrating on insects, although they dig less, and, when going for plant matter, are more likely to climb trees to get at dates or chew the leaves of succulent plants than they are to dig up the roots. Largely nocturnal, they avoid the heat of the day by burrowing into the ground, changing sites about once every five days - although the female digs much larger, longer-lasting burrows when she has pups to rear. (The father, although he certainly brings his pups food, plays with them, and so on, apparently lets his partner do all the digging. Babysitting is one thing, but major construction is clearly woman's work).
Heading further south, we come to one of the least studied and most mysterious of all the members of the dog family: the pale fox (Vulpes pallida). About the same size as Rüppell's fox, it can be most easily distinguished by having a black, rather than a white, tip to its tail, although it also has a paler colour overall and ears that aren't quite so large externally. (Internally, however, the ear chambers are actually larger, suggesting that it has a good sense of hearing).
Pale foxes live in the Sahel, a band of semi-desert environment that separates the Sahara from the lusher tropics further south, and they are found across the whole of the continent, from Mauritania and Senegal in the west to Eritrea in the east. One of three species colloquially known as "sand foxes" (the others being Rüppell's and the Tibetan fox), they do seem to prefer very dry habitats, and, like their cousins further north, don't seem to need to drink.
They appear to be largely herbivorous, preferring things like wild melons, but, naturally enough they also eat insects and small vertebrates from time to time. They are nocturnal, resting in burrows during the day, which can be 15 metres (45 feet) long and 3 metres (10 feet) deep. They seem to share these with relatives at least, and so are presumably fairly gregarious, but that's about as far as our knowledge goes. They may, perhaps, be better known to the Dogon people of Mali, who apparently use their traces in divination rituals.
Like them, it is omnivorous, but it also maintains separation from the medium-sized carnivores of the area by preferring to feed on mice and rats. This leaves other prey for its potential competitors, ensuring that there's enough food for all of them without having to fight too much. Of course, despite their preference, Cape foxes do eat other food, too, and they are large enough to catch and eat the local hares, which would likely be well beyond any of the desert species to the north, even were they available there. They are hardly top predators, though, themselves frequently falling prey to the local jackals.
Socially, Cape foxes are monogamous, with each mated pair sharing a territory separate from that of their neighbours, but still hunting on their own. Males leave home when they are old enough, or when their mate dies, suggesting that it's largely the female that maintains the territory, allowing her partner to share it while he is around. They communicate with one another largely by means of a high-pitched howl, although females also bark to warn off intruders approaching the den where she hides her pups.
They are capable of breeding throughout the year, although the constraints of the climate mean that not all do so, with some restricting themselves to times of the year that will give their pups the best chance in life. They raise their young in burrows, which they often dig themselves, but sometimes pinch from aardvarks or hares. In some harsher terrain, such as that on the edge of the Kalahari Desert, these can apparently become large communal burrows, shared by neighbouring pairs, but this is an unusual occurrence.
The ability to eat more or less whatever they come across is doubtless a large part of what allowed foxes to enter desert environments in the first place, evolving to suit them better on at least three occasions - once each on the lines leading to fennec and Blanford's foxes, to Rüppell's fox, and to the kit fox of North America. It's also likely what helped the Tibetan fox adapt to its desolate high-altitude home. There is, however, another habitat that is similarly hostile, but in almost the opposite way, and to see how foxes adapted to that, too, we need to head out into the Arctic...
[Photos by Drew Avery, Jesper Särnesjö, and Jeppestown, from Wikimedia Commons. Painting by J. G. Keulemans, in the public domain. Cladogram adapted from Lindblad-Toh et al, 2005 and Bardeleben et al, 2005.]