Sunday 5 November 2023

Skunks of the World: Stink Badgers!

Sunda stink badger
As I mentioned at the beginning of this series, for most of the 20th century, skunks were thought to be mustelids, members of the same animal family as weasels, polecats, badgers, and the like. They were given their own family in the 1990s, once it became clear that racoons were more closely related to mustelids than they were. But the genetic analyses that revealed this fact also provided another surprise.

It had been assumed that skunks (as a subfamily of mustelids) lived only in the Americas, much as racoons do. But the genetic studies showed that two species of supposed badger living in Indonesia were not, in fact, badgers at all, but members of the newly erected skunk family. These animals are collectively known as "stink badgers", although the local name of "teludu" and "pantot" are sometimes preferred.

It might seem odd that we'd mistake a skunk for a badger, and in fact, the story isn't quite that simple. For one thing, when Anselme Desmarest first scientifically described the animal in his 1820 work on the mammals of the world, he identified it as a skunk, placing it in the same genus as the American animals. For another, at least one study in the 1970s suggested that stink badgers might be closer to skunks than they were to other badgers. This was based on their brain anatomy, with skunks and stink badgers both having the parts of their brains dedicated to smell enlarged compared with "other" mustelids.

Set against this, we have the fact that skunks, so far as was known, were otherwise unique to the Americas, and that stink badgers don't really look much like them. While modern studies are unequivocal that, yes, they really are skunks, they split off from the other members of their family around 10 million years ago, probably when the latter wandered across a land bridge into North America.

By far the more widespread of the two species is the one that Desmarest originally named, the Sunda stink badger (Mydaus javanensis). This is currently divided into three subspecies, one living in Sumatra and Java, one in Borneo, and the third on the Natuna Islands between Borneo and Peninsular Malaysia. Even today, it is apparently one of the most commonly seen carnivorous mammals in these islands and hunting is sufficiently low-level (although not non-existent) that it does not appear to be under threat.

Having said that, especially compared with North American skunks, we don't really know all that much about it, and it's probably not quite as widespread as it once was. Stink badgers are about the same size as striped skunks, only weighing around 2.5 kg (5 lbs 8 oz.), but otherwise have the stocky build and short, muscular limbs we would expect of a badger. They are very dark brown in colour, rather than black, with a white or off-white patch of fur on the head and, sometimes, a narrow white stripe down the back. The tail is white and has far shorter fur than that seen on other skunks; there is no "bottlebrush" threat display seen in other skunks. The narrow, slightly elongated, head is almost hairless on the snout.

And, yes, as their name suggests, stink badgers are more than capable of spraying potential threats with a noxious fluid from their anal glands. This does not appear to have been analysed in any detail that I can find (although some of the components are used locally in perfumes - presumably in very small quantities) but it's said to be potent enough to blind or even asphyxiate dogs. While this might sound like a clue to their skunky nature that we should have spotted earlier, it's worth noting that zorillas can do the same thing - and they really are mustelids.

Despite their generally wild distribution stink badgers are not common in the dense primeval forests that cover much of their native islands, preferring more open woodland, whether that be because it is on the natural periphery of denser jungle or has been partially cleared by human activity. 19th-century accounts reported them at elevations of over 2000 metres (6,500 feet) but they also seem common in the lowlands, perhaps down to sea level. They may inhabit caves in the mountains, but more commonly use burrows, whether those they have dug themselves or appropriated from other animals. These are not the deep complex burrows of European badgers, not least because stink badgers at best live in pairs, rather than communal setts, and are usually no more than 60 cm (2 feet) deep. 

Stink badgers are nocturnal and omnivorous. In the wild, they feed on insects, worms, eggs, and carrion, alongside whatever plants may be local to the area. Earthworms seem to be their preferred food, and they spend a fair amount of their time rooting around in the soil with their hairless snout and large fore-claws trying to find them. It has been suggested that the distribution of stink badgers is influenced by places where the soil is best suited for earthworms, although the evidence for this is currently weak.

Most of their other habits remain a mystery, at least to Western science. The females have six teats, which suggests a maximum litter size of that number, but two or three young is apparently more typical. Presumably, these are raised in burrows, but the details remain unknown.

Palawan stink badger

The second species was not identified as such until 1887. The Palawan stink badger (Mydaus marchei) lives only in the southwestern Philippines, on Palawan and the Calamian Islands. For a while in the 20th century, it was considered distinct enough to be given its own genus, but it's hard to see why, since the two species are difficult to tell apart. The Palawan species is slightly smaller, with adults weighing about 2 kg (4 lbs 4 oz.), with a shorter tail, and ears that are so small as to be almost invisible... but otherwise, it's essentially the same as its more widespread relative.

We know even less about the Palawan species than we do the Sunda one and the little we do know suggests that they're behaviorally, as well as physically, similar. They inhabit lowlands (there are mountains on Palawan, but they only just reach 2,000 metres, so the badgers couldn't be found higher than that anyway) including grasslands and swamp as well as open woodland. While the Sunda species apparently avoids plantations, the Palawan one does not similarly avoid rice paddies, especially where they are close to scrubby bushes suitable for hiding in. They are said to eat molluscs and small crabs as well as the same types of food eaten by their relatives.

When approached by humans or other potential threats, they snarl and stamp their feet, much as a regular skunk would. One individual was reported to pretend to be dead when a researcher touched it... but when he tried to pick it up and carry it elsewhere, it eventually decided to spray him. Oddly, he later said that the smell was "pungent but not offensive", comparing it to almonds and certain kinds of ant. He also saw the badger using the same secretions to mark the trails it walked along, so it's likely that it isn't purely defensive as it is in regular skunks.

All of which represents essentially our entire knowledge of the species. It also brings me to the end of the living members of the skunk family. We do know of some fossil skunks, however, with the oldest North American example being Martinogale, which lived in California about 9 million years ago, and either was, or was closely related to, the first skunk to reach the continent from Asia. It was about the size of modern spotted skunks - that is, quite a bit smaller than the striped sort - and, despite some primitive features, probably already looked very skunk-like. Obviously, we can't know how good it was at spraying from what's basically a well-preserved skull, but every living skunk is, so it's a fair bet.

Martinogale is followed by Buisnictis, which is known from Mexico to Kansas, and lived from around 5 to 2 million years ago, during the Pliocene. Its teeth more closely resemble those of modern American skunks, and it could even be their direct ancestor. (We can't know this, of course, but at present, we have no other candidates, so it's at least plausible). It's likely that the first skunks crossed into South America, to give rise to the hog-nosed species of today, around 2 million years ago when the Panama land bridge opened up, with the striped and spotted skunks of the north diverging from one another not much later, perhaps when they were separated by the advancing ice sheets.

The origin of the stink badgers is less clear, since we lack any fossils showing clear relationships to them. However, we can be confident that skunks first appeared in Asia and headed east, rather than going the other way, because some of the Asian fossils we do have are older than Martinogale and this also fits with what we can infer of their origins from mustelid-like animals. The best-known of these is Promephitis, which first appeared around 11 million years ago and survived right through to the start of the Ice Ages 2 million years ago. That's far too recently for it to be the ancestor of stink badgers, and its precise placement within the family is unclear. Similar in size to a modern striped skunk, it lived across Eurasia from Greece to China showing that skunks were once widespread on this continent. Indeed, Palaeomephitis, which lived 12 million years ago in Europe, may be the oldest known skunk, but its remains are sufficiently fragmentary that we can't currently be sure.

In any event, genetic evidence suggests that skunks are much older than this, likely having first appeared some time during the Oligocene, around 30 million years ago. The gap between this date and the oldest known fossils is large enough that we can't be sure when the powerful stink glands would have first appeared - for all we know, they may be a feature of the one branch of the family that survives, arising relatively recently in the common ancestor of stink badgers and American skunks. 

Skunks, raccoons, and mustelids together form an evolutionary group called the "musteloids", a collection of smallish carnivores that often, but not always, tend towards omnivory. However, not all living musteloids fit into one of these three families. There is one exception, and I will round out the year by taking a look at the odd one out...

[Photo by "U.Name.Me" from Wikimedia Commons, drawing by J. Huet, in the public domain. Cladogram adapted from Caro et al. 2012 and McDonough et al 2022.] 

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