Fox week, day 3: Two other species

December 4, 2013 • 6:38 am

What a great group of readers I have! I complained about my dearth of fox pictures, and what happens? Ceiling Cat sends me readers bearing gifts of fox pictures and videos, including species other than Vulpes vulpes.  In fact, I now have more than enough pictures for a week; but if you have some good ones, I’ll still accept them.

Today I’m featuring species besides the familiar red fox (but Reynard will return).  First, we have three bat-eared foxes (Otocyon megalotis) from reader Bob Johnson, photographed by him in Kenya in 2008 (click to enlarge):

Bat eared fox 1

The bat-eared fox has a disjunct range in Africa, with each of its two regions representing a separate subspecies (O. m. megalotus in the south and O. m. virgatus in the east).  Its ears are large (about 13 cm, or 5 inches), as is usual for foxes inhabiting warmer climes.

The observation of longer extremities in related species (or in populations of a single species) in warmer habitats is called “Allen’s rule.” It holds for warm-blooded animals like mammals and birds, and that should be a clue to its evolutionary significance. Try to guess the answer without Googling. There two possible answers, both of which may hold:

Bat eared fox 3

The range:


Like the fennec below, the bat-eared fox is largely insectivorous, dining mainly on termites. It’s also monogamous and, unusually, males do most of the parental care—at least according to Wikipedia.

Bat-eared fox 2

The fox with the longest ears relative to body size is the fennec (Vulpes zerda), which lives in the Sahara desert (the reason for those crazy ears).  The species is nocturnal, and 80% of its diet consists of termites.

It’s the smallest of all foxes (1.5-3.5 lb, or 0.7-1.6 kg), weighing less than an average housecat. It’s my favorite of all foxes because it’s adorable, furry, and the most catlike of canids. Here are two pictures taken from the web. The second is a cub, whose ears look even more ridiculous because all dogs and cats have relatively larger ears when they’re young:




And, from the other half of the world, an Arctic fox—also snapped by Bob during a trip to Churchill, Manitoba this November (I posted one of his polar bear snaps from the same trip here).

Arctic fox 1

The species name is Vulpes lagopus, and it has a pan-Arctic range:


As you see, this species has much smaller ears, and the selection pressures involve at least one environmental factor that drove the evolution of large ears in desert foxes. Its tail is also bushy, and during the cold Arctic winters (animals can tolerate temperatures of -50 C), it wraps its tail around its head like a muffler. It’s snout is also relatively less pointed than that of foxes in more temperate climes—for the same reason why the ears are small.

Unlike the fennec or bat-eared fox, this one is a carnivore, dining on small mammals like rabbits, mice, and voles.

Another adaptation of this species is that, like many Arctic birds and mammals, it changes color with the seasons, being white (as above) during winter, and turning grey or brown in summer. That is also adaptive and simply can’t be explained by genetic drift (pay attention, Larry Moran!), for it’s a parallel trait seen in many Arctic animals. And the adaptive significance is clear.

There are also two morphs: the regular one (‘white’) and a ‘blue’ morph that lives in more coastal regions, though both can be found in the same place, as seen in the picture below. The blue color is due to homozygosity for a single recessive gene.  Blue foxes, prized for their pelts, were moved to the Aleutian Islands en masse to try to preserve the morph.

Blue Morph and White Arctic Foxes

30 thoughts on “Fox week, day 3: Two other species

  1. Years ago, when driving along some back roads in Mexico, our group came across another fox species which I would tentatively call a kit fox (Vulpes macrotis). It stepped out on the road just ahead of us, looked startled, and was gone in a flash. It too showed Allen’s rule rather nicely.
    I know the answer as to why big ears and long skinny legs are adaptive, but I will leave it to others.

      1. No. Some other mammals sweat as well (as evident to anyone who’ve seen a horse after a run). Apes have sweat glands as well, but not as many as human, and not all over the body.

  2. I loved the bat- eared foxes I saw in Kenya and Tanzania in my early 20s. For some reason I first heard it as BAD- eared foxes, and have to keep reminding myself that they’re not badass…

    1. Bate eared foxes in southern Africa can be twice the size of eastern ones – the first ones I saw in east Africa are so tiny in comparison that I squealed embarrassingly at their cuteness. That disjunct range is common to many animals in Africa – the eastern and southern arid zones were once linked and are now split by mopane forests and other habitat types. Aardwolf for example show a similar distribution to bat ear foxes, and there are sometimes different species filling similar niches: eusocial naked mole rats in the east, eusocial Damaraland mole rats in the south. Unfortunately, bat eared foxes love foraging for bugs in roads and are common roadkill in South Africa

  3. I strongly suspect that adult fennec fox is a resident of the Phoenix Zoo. The animal, the background, and even the shooting angle and perspective all fit my memory….


  4. I’m pretty sure it’s heat regulation. Our d*g has a very short snout and is small with lots of hair. We have read to be watchful for ambient temp extremes as a result.

  5. The fennec foxes are very cute with their big ears & little bodies but arctic foxes are quite lovely as well….well all foxes are really.

    From what I remember learning of Allen’s law is that the adaptation is to do with heat conservation as well as not getting your extremities nipped off in the cold. When I learned about it, it was in a physical anthropology class so the examples given were tall slim humans that lived in warmer climates like India versus shorter limbed humans who lived in climates like the tundra regions of north america (at the top cold parts).

  6. These fox photos are so wonderful! You really do have some wonderful followers that are able to supply such great photos! I’d never even heard of the “blue” morph of the artic fox before now. I’m intrigued to look into this further!

    Thank you for sharing the wonderful things you share here. I’m a fairly new reader, and becoming a big enthusiast of evolutionary biology!

  7. Temp regulation. Was it this site that featured a video I viewed last week of an arctic fox listening with its northern latitude-sized ears for mice activity under 3 feet of snow? That video seems to disqualify enhanced hearing, due to large ears, for hunting small rhodent prey as a feature of evolutionary adaptation. If I hadn’t seen that video, I might have first guessed the ear size is for hearing only and moved on, never considering capacity as an animal temperature radiator.

  8. I recently saw a documentary about arctic foxes and their tough lives. I found them to be most beautiful foxes, especially when they don their white winter coat!

    Fennec foxes are also most endearing. The photo of the little Fennec pup reminds me of a Mogwai before it turns into a Gremlinn!

  9. Fox experience. I live in western Napa County CA. Lots of foxes hereabouts. both Red and Grey .Hybrids?
    A neighbor found a Red Fox on my place with it’s head stuck in a empty gallon jar of mayonnaise. It had worn itself out trying to get it’s head out. My neighbor held the fox while I used a pair of tinsnips and we freed it.
    I actually think it was grateful as it did not try to bite.

  10. As I understand it, the blue morph is due to a dominant gene. I have long understood that it was lethal when homozygous, but I have not been able to confirm that by googling.

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