Saturday, 29 September 2012

Weasels on the Savannah: Zorillas and their kin

Saharan striped polecat
Even before we had good molecular and genetic evidence for how the various members of the weasel family were related to each other, there were a number of different schemes proposed for dividing up the family into smaller groups. Otters were almost universally agreed to be something different from the other weasels, and, in the simplest scheme, everything that wasn't an otter was considered a "musteline". Once the genetic information arrived, it wasn't a terribly great surprise to learn that the martens were a group, the 'true' badgers were a group, and so on. Removing badgers, martens, and the like, meant that the term 'musteline' now referred only to the weasels themselves, and their closest relatives: stoats, polecats, and mink.

What was rather more surprising though, was that one group of what seemed to be quite clearly weasel-like animals actually constituted an entirely separate branch of the family tree. Mostly living in the southern hemisphere, it had not really been obvious before that these animals were especially closely related to one another. Because of that, unlike badgers, otters, and martens, they had no collective name in English. The scientific term for members of this group is "galictines", and that remains the best word we have for them.

Three of the six species of galictine even have words such as 'polecat' and 'weasel' in their common names, because that's what we thought they were before better evidence came along. In reality, other than belonging to the same overall family, they aren't that closely related to 'real' polecats and weasels. Our understanding of their exact relationship to other members of the weasel family is somewhat in flux; they are clearly closer to mustelines and otters than they are to, say, badgers, but the picture may not be as simple as first thought. I'll have more to say on this in a later post.

But what are these creatures? For the most part, they aren't that familiar to people in the west. Many of them live in Africa, and, while we're all familiar with lions, gazelles, and elephants, the smaller wildlife tends to be somewhat overlooked. (Except meerkats. Everyone likes meerkats).

When you look at a zorilla (Ictonyx striatus), it's easy to see why it was once thought that skunks were also members of the weasel family. Zorillas are around the same size as the most familiar North American skunks, and have the same bushy tail and similar black-and-white markings. They are found throughout most of sub-Saharan Africa, and, while they seem to prefer savannah, veldt, and light forest, are also found in mountains, swamps, and agricultural land. In fact, the only environment they really avoid is tropical jungle, and they are therefore absent from central Africa and from the tropical south coast of western Africa. Otherwise, though, they are found pretty much everywhere, and, like many other weasels, they are obviously quite adaptable animals.

The distinctive, and highly visible, coat patterns of skunks serve as a clear warning to any predator that doesn't want a face full of stink, and zorillas are no different. Apart from the sea otter, all mustelids have a scent gland beneath the tail. Many species use this to defend themselves, but in zorillas it's particularly well-developed. Zorillas try to deter larger predators by fluffing their tails up to make themselves look bigger, but if that fails, they will spray them with their anal glands, just as a skunk would. The spray includes foul-smelling sulphur chemicals, and, while some sources say it isn't quite as bad as the smell of a real skunk, others (especially on the internet) claim that it's actually worse. Either way, it evidently stinks so badly that the fine details probably don't matter that much to anyone on the receiving end.

A large proportion of a zorilla's diet consists of insects, including beetles, flies, grasshoppers, and the like. They are also quick and agile enough to catch moths, pinning them to the ground with their fore-feet before eating them. However, over a third of their diet typically consists of small mammals, such as mice and ground squirrels. They hunt, as many animals do, with a combination of sight and smell, and can use the strong claws on their forefeet to dig rodents out of their burrows to eat them.

They don't seem very choosy about their food though, and they will also eat birds, reptiles, and eggs if the chance presents itself. Some of these can be quite large, and they have been reported to take on snakes, pouncing on their back and delivering a series of savage bites to the body some distance away from the head and its deadly fangs.

Like most members of the weasel family, zorillas are highly antisocial, and adult males are said to be particularly aggressive towards one another. Nocturnal animals, although they are capable of digging burrows if they have to, they prefer to spend the day in crevices and hollows that are naturally available - including under houses or sheds, if that's what's around. During the night, they hunt on the ground, although they are said to be good at both climbing and swimming, if they really have to.

They mate in the spring, giving birth just 36 days later - there is no need for the protracted delayed pregnancies of more northerly mustelids in their warm and balmy climate. The young are initially blind and hairless, developing their stripy coat after a couple of weeks. A mother looking after her litter of two or three young is about the only time you'll see more than one zorilla together outside of the mating season.

Another name for the zorilla is "striped polecat", although, now that we know that, whatever else it may be, it isn't a polecat, the name is beginning to fall out of favour. Another problem is that there's another, very similar animal also called a "striped polecat". To distinguish the two, the latter is often called the "Saharan striped polecat", the "North African striped weasel", or combinations of those terms. Unfortunately, its scientific name is also in dispute, due to a lack of clarity as to which genus it belongs. Many older sources prefer Poecilictis libyca, stressing its difference from other species, while most newer sources prefer Ictonyx libycus, emphasising its close relationship to the zorilla.

The problem with the latter name, at least in my opinion, is that it's almost certainly wrong. The exact position of striped polecats in the weasel family tree is far from clear, but there do seem to be very strong grounds for assuming that, no matter what else it might be, it isn't an especially close relative of the zorilla. So I'm going to stick with P. libyca.

In fairness, that's based on fairly recent evidence, and its easy to see why this hadn't previously been suspected. Saharan striped polecats look remarkably like zorillas. They are quite a bit smaller, being closer in size to a stoat than a polecat, but they have essentially the same coat pattern and physical appearance. Not only that, but they can spray foul-smelling liquid just as effectively as a zorilla can, and it may be that the coats are similar for exactly that reason - potential attackers just need to remember the one pattern to stay clear of.

As the "Saharan" (or "North African") part of their name implies, these animals live further north than zorillas. They don't inhabit the heart of the desert, but they do live in rocky semi-desert environments, and coastal sand dunes, right along its fringes, from Egypt in the east to Morocco in the west, around the west coast, and then along the southern edge of the desert from Mauritania to Eritrea on the coast of the Red Sea. Like zorillas, they are nocturnal, although they seem to have a greater preference for vertebrate prey, eating rodents, small lizards, and birds at least as much as they eat insects.

They are good at digging, and use their claws both to dig out prey and to excavate their burrows. Like zorillas, they breed in the spring, although the length of pregnancy seems to be somewhat variable. They are said to be solitary, aggressive, and persistently smelly, and Walker's Mammals of the World advises that they "do not make good pets". Well, quite.

African striped weasel
The third African species is the African striped weasel (Poecilogale albinucha), another black-and-white striped animal, and one that is rather larger than the moniker 'weasel' might suggest. It is longer than the Saharan striped polecat, but much more slender, with the short limbs and lengthy tail of true weasels, rather than the more skunk-like appearance of zorillas. It lives south of the equator, in savannah and grasslands, although it may occasionally wander into light forest, or agricultural land - where it may be helpful, by keeping down mice, rats, and even locusts.

It primarily eats small rodents, although, like its relatives, it also preys on small reptiles, insects, and so on. It apparently doesn't run very fast, and so prefers to track its prey by following their scent trails, and only pouncing on them from short range. However, as with true weasels, its long and slender body means that it can easily fit into burrows of animals smaller than itself, enabling it to pursue them underground. Sometimes it takes over these burrows for its own use, although it also a capable digger, and can construct its own dens when needed.

As the coat pattern suggests, it too can spray foul-smelling liquid on its attackers, although apparently the resulting stench is much less severe than that of skunks or zorillas. They are nocturnal, and slightly less anti-social than their relatives - although males will fight each other at every opportunity, male-female pairs seem to get along well enough, even outside of the spring/summer mating season.

Marbled polecat
Moving north to Asia, we come to the marbled polecat (Vormela peregusna) , one of the most distinctive of all mustelids. They are about the same size and shape as the local polecats, and have a similar 'mask' pattern on their face. However, their back has a variable 'marbled' pattern, being a bright yellow with multiple red-brown blotches. The exact pattern of the blotches can be used to identify different subspecies, although this does not appear to be wholly reliable. Indeed, dominant males change colour during the breeding season, with the coat becoming a richer orange. They are apparently somehow able to prevent weaker males from doing the same, because a subordinate male kept on its own will develop the orange colour, while one in the presence of more powerful males will not.

Marbled polecats live in semi-arid environments, including open steppe-land, rocky hills, and thorny scrub. They are found in a band across Asia, from northern China, through Central Asia and the Middle East, and as far west as the Balkans, where they are especially common in Romania and Bulgaria, but are also occasionally found in neighbouring regions such as Greece and Serbia. They are not particularly common, perhaps because their chosen habitat can't support a high population, and they are sometimes hunted for their fur, or out of fear that they will kill domestic chickens, and are currently considered a 'vulnerable' species.

Like many of their kin, they are nocturnal, and they can dig their own burrows to shelter in during the day. They feed mainly on mammals, such as mice, wild hamsters, and gerbils, but, also like their kin, will make do with whatever they can get. At least some switch diets at different times of the year, as different foods become available. They do have anal scent glands, but, despite being a particularly close relative of the zorilla, these don't seem to be any more potent than those of most other members of the weasel family.

Pregnancy lasts up to ten months, so clearly some form of delayed implantation is involved, as is common with mustelids outside of tropical climes. The litters are also larger than those of the African species, with six to eight young being common. They are solitary, but not especially aggressive towards one another, although they are said to emit a loud growling shriek when angry or frightened.

The word 'galictine' derives from the genus Galictis, which contains the remaining two species of the group. What's surprising, though, is that these animals live in South America, a long way from their Old World kin. It's evident that they split from the remaining galictines fairly early on, but, even so, it's surprising that they live so far apart. More recent evidence casts doubt on how closely related the South American species really are to zorillas, but it doesn't really help matters, because it still shows a clear link with the other African species.

Greater grison
Whatever the molecular evidence may say, the greater grison (Galictis vittata) doesn't look too much like its striped African relatives, either. It's considerably larger, for one thing, somewhere between the size of a ferret and a badger. Its body form is somewhere between the two as well, being slender yet muscular, with a moderately long tail and a head that's more weasel-like than badger-like. The colour, however, is closer to that of a honey badger, with jet black face and underparts, and a grey back sharply cut off by a white stripe down the side of the head and neck.

Greater grisons are forest-dwelling animals, but are adaptable enough that almost any type of forest will suit them, from waterlogged lowlands to steep-sided mountains. They live in the northern and central parts of South America, east of the Andes, and up through Central America as far as eastern Mexico.

Lesser grison
The closely related lesser grison (Galictis cuja) lives further south, from southern Brazil and Bolivia down to at least central Argentina, and possibly almost to the very southern tip of the continent. As its name suggests, it is smaller than the greater grison, although not by very much, and it also has a brownish, rather than grey, back. Although it, too, seems to like forests, it regularly hunts in more open terrain, retreating to heavier cover once it has eaten. Given how far south it lives, a heavy reliance on forest would doubtless be far more limiting for it than for the larger species.

Both species are good diggers, and often inhabit burrows up to twelve feet deep, which they may share with their relatives - although they have little to do with one another when above ground, preferring to hunt alone. They feed on whatever they can catch, although inevitably rodents such as mice, wild guinea pigs, and chinchillas are frequent features on the menu. Greater grisons, in particular, will also tackle somewhat larger prey, and have been observed eating such things as agoutis, poison-skinned toads, and even piranhas.

Unlike the other galictines, they are active during the day, not the night, although they may take a snooze at midday. As their ability to catch and eat piranhas shows, they are good swimmers, and they are also fairly agile in the trees, although they do most of their hunting on the ground. They seem to breed all year round, with litters of up to five young, and mature rapidly. Their fur, fortunately for them, has no commercial value, and they are sometimes kept as pets, being used like ferrets to chase animals from their burrows.

[Picture of striped polecat © Bibliotheca Alexandrina, released under Creative Commons license BY_NC_SA 3.0. Other pictures by "Devonpike", "Wgors", Tony Hisgett, and Ken Erickson, from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008.]

1 comment:

  1. Being very fond of all things mustilid I have to say I really really enjoyed this article. Thank you so much.