Sunday 5 August 2012

Weasels in Burrows: the 'True' Badgers

European badger
The word 'badger' has been applied to a number of species of stocky, moderately sized, members of the weasel family, that are not necessarily all closely related to one another. That's not due to any sort of carelessness with the names, because, for a long time, it was thought that they were closely related.

It's hardly an unreasonable conclusion, because they do look strikingly similar to one another, even to the extent of having similar coat markings. Modern genetic analysis, however, has shown that they are rather more different from one another than appears at first glance. Indeed, one group of 'badgers' - the stink badgers - turned out not to belong to the weasel family at all, but, instead, to the skunk family.

The stink badgers are obviously beyond the scope of this series on mustelids, but the various other species are not. The remaining badgers, however, still do not constitute a single group within the weasel family, as was once thought. That's because they don't have a single ancestor from which all other badgers - and crucially, nothing but badgers - are descended. All badgers are related, because everything is related, if only you go back far enough, but they're often more closely related to other animals than they are to each other.

Having said that, many badgers do belong to a single subfamily, officially called the Melinae, or 'meline badgers'. This includes the first badger species to be scientifically described, and takes its name from the genus Meles, to which that species (the European badger) belongs. Since the word 'meles' is simply Latin for 'badger', it also seems reasonable to describe this group as the 'true' badgers, with the others being animals that just happen to resemble them.

Although many other members of the weasel family dig burrows, badgers are highly suited to this task, and are the most powerful and effective diggers within the family. This is apparent in their relatively large, muscular bodies, and their short limbs and tails. Unlike other weasels, badgers walk entirely on the soles of their feet (although some of the martens do come close to this gait, without quite fully managing it). The forefeet have powerful claws for digging through the soil, although the hindfeet, which simply push the excavated soil out of the way, are less modified.

European badgers (Meles meles) are surely among the most familiar of all wild mammals to British readers. This is due to their remarkable tolerance of human activity; while their preferred natural habitat is woodland, they are highly adaptable, and are commonly found in agricultural land, suburban gardens and city parks. While they are nocturnal, and rarely seen during the day, they remain, with the possible exception of foxes, the most easily seen wild animal in the UK without even having to head out into the country. Charities such as the Badger Trust exist specifically to support their welfare, and there are numerous local badger watching groups across the country.

These are the badgers of Wind in the Willows and of Hufflepuff, instantly recognisable from their appearance. It's not at all clear why they have those stripes on their face, although the fact that so many other badger species have them too indicates that there's presumably a good reason. The most favoured suggestion is that they may be a warning to other animals that they're capable of fighting back if attacked, and are best left alone, but they could also have a social purpose or even help to protect the eyes from glare.

There are a number of sites about European badgers, such as badgerland, on the internet, and numerous readily available books about them, so I'll pass them by without too much further comment. However, because its so unusual for members of the weasel family, their social system deserves some mention. With the exception of some otters, mustelids are generally solitary, avoiding each other's company outside of the breeding season, and barely tolerating it then. European badgers, however, are a different matter - but why?

A significant clue may come from the fact that they aren't quite as sociable as you may think. European badgers are found throughout continental Europe west of the Volga River, as well as on a few islands of the Aegean Sea (although not on Sicily, Corsica, Sardinia, or the Balearic Isles), and in the Middle East from Turkey, Lebanon, and Syria, through northern Iraq and Iran as far across as Afghanistan. Across most of this range, they don't live in particularly large groups, and, especially on the margins, they are actually solitary.

Yet, in Britain and Ireland, they live in clans of up to two dozen individuals. The key factor is probably the climate. European badgers will eat almost anything - unlike other mustelids, up to 50% of their diet consists of vegetable matter - but they particularly like earthworms. It seems that in Britain, the frequent rain and lush natural vegetation is good for earthworms, and, indeed, for most of the other things they eat. As a result, the population density of badgers in Britain is far higher than in any other country, and there's so much to eat that they find themselves pushing up close to one another without having to share much food. Social living seems to simply be a solution to that, allowing them to make full use of what's available.

Indeed, groups of European badgers are not especially hierarchical, compared with many other group living animals, such as wolves. There is generally a dominant male and female, but individuals tend to sleep apart in different chambers within the sett, and they don't, for example, compete much for mates. In fact, what seems to happen is that, when young badgers grow up, they simply don't bother to leave home, because there's enough food around for them not be competing with their own parents. As a result, setts grow over the generations, with tunnels reaching hundreds of metres in length, and new chambers being added over time. Crucially, this is not what happens outside of the UK, where young badgers often leave home as soon as they are able.

As a result, the badgers in a sett will all be closely related, so that they have to wander off to find new partners when it comes time to breed. Both males and females will mate with several different partners when they get the opportunity, making it pointless for the males to fight over the privilege, and even litter-mates may have different fathers.

Within a group, European badgers recognise each other by scent. Like other members of the weasel family, they have well-developed anal scent glands, which they use to mark, not only the bounds of their shared territory, but also each other. This helps to identify kin, since they will fiercely defend their territory from outsiders, and cooperatively mark the borders to ensure that they do not inadvertently leave any gaps.

There are subtle differences in the appearances of badgers across their range, and over twenty different subspecies have been identified at one point or another, although it's far from clear how real they all are. Certainly, there is a fair degree of genetic variability among them, and its interesting to note that Irish badgers have greater kinship with those in Spain and Scandinavia than they do with those in Great Britain - evidently, there were two different re-colonisation events after the retreat of the glaciers at the end of the last Ice Age

Many were originally described as entirely separate species, back in the nineteenth century when systematic zoology was relatively new. Later, in the twentieth century, they were all merged back into a single species, said to inhabit, not just Europe, but also much of Asia. The species was identified as the "Eurasian badger", and many sources, both online and in print, still use this old term, and will tell you that Meles meles is found far beyond Europe and the Middle East.

Genetic studies, beginning in 2002, have since shown that these animals represent at least three different species, of which the European badger is only one. The Volga River is thought to be the boundary between the European species in the west and the Asian badger (Meles leucurus) in the east. The river is too wide for them to easily cross for much of its length, although the two do live together along its upper reaches, and perhaps as far east as the Kama River.

Asian badgers are smaller, slimmer, and lighter in colour than their European kin, but otherwise appear extremely similar - which is why it took so long to confirm they are a different species. They live across central Russia, Central Asia, much of China and Mongolia, and into Korea and the neighbouring Russian Far East. It's assumed that their habits are similar to those of European badgers, too, but we don't really know for sure.

That's because, since they weren't thought to be a separates species until ten years ago, nobody bothered to do much specific research into their habits. In fact, even among European badgers, most of the research has been done in Britain, leaving the habits of their less sociable kin elsewhere in Europe less clear.

In comparison with Asian badgers, we do know a little more about the third species, the Japanese badger (Meles anakuma). Somewhat smaller than European badgers, these have a browner cast to their fur, and less distinct facial stripes, but, again, they are sufficiently similar that, even today, there is dispute about whether they truly are a separate species or not.

Their biology is generally similar, too. For example, they eat a similar mix of food, with a preference for earthworms, and, at the right time of year, persimmon. Like European badgers, their native habitat is forests, but, while they also venture into the suburbs, the growth of Japanese cities has led their population to decline over the last few decades.

Japanese badger
Their social behaviour, however, is notably different, at least from the well-studied badgers of Britain. Japanese badgers live in small family groups, consisting of a mother and her offspring. Males apparently live on their own once they reach adulthood, and maintain territories that keep out competitors, while allowing them to visit a small number of local females. Setts are correspondingly smaller, since they are really only used for raising young, albeit the young badgers will continue to live with their mother for over a year after they are weaned.

Furthermore, during the winter, Japanese badgers enter a state much closer to true hibernation than European badgers can manage. The latter are torpid during the winter, staying inactive and not moving outside their setts, but Japanese badgers seem to have a rather more dramatic reduction in their body temperature, and to remain quiescent for a greater portion of the year.

While the Asian and Japanese badgers have often been considered the same as the European species, the same is not true of the remaining species of 'true badger' which is distinctive enough to be clearly different. The hog badger (Arctonyx collaris) lives in China, South-east Asia, and Sumatra, where it inhabits forested, and often hilly, habitats. However, there is an important caveat: a survey of museum specimens in 2008 concluded that, just as with the Eurasian badgers, there may actually be three different species of hog badger.

These species have been identified purely on the basis of their physical appearance, which apparently shows distinct changes from the small, dark hog badgers of Sumatra, to the shaggy animals of China and Tibet, and the unusually large, paler and short-furred ones living in between. This discovery is too new to have propagated through the usual lists of species, so it's unclear how widely it will be accepted. Perhaps the best indication of the status of these 'new' species will come next year, when the IUCN Red List is due for a major review and revision.

For the moment, however, let us treat the hog badgers, as almost all sources still do, as if they are a single species. Their affinities to the Eurasian badgers are obvious, for they have a similar build and size, and similar coat patters, including the two narrow black stripes across the eyes. They can be distinguished from the other 'true' badgers, however, by the fact that their tail and throat are white, rather than greyish and black, respectively. Their snout is narrower, and ends in an elongated pink, hairless tip, with which they snuffle through leaf litter, much as pigs do (hence their common name).

They eat similar food to European badgers, although with a greater preference for meat, and apparently, also with a particular liking for snails. Although they have the same powerful, digging claws that European badgers do, they don't seem to use them so much, and they often spend the day in natural shelters, rather than excavating their own burrows - although they are certainly capable of doing so. Like other 'true' badgers, they are nocturnal, and, at least in China, they hibernate through the winter.

They are quite unlike their kin, but much like most other weasels, in being solitary animals that never gather together for any length of time, except for females raising young. Even that lasts only for the four months or so it takes for the pups to be weaned; as soon as they no longer need milk, they leave their mother for a life on their own.

While none of the 'true' badgers are endangered, or even close to that status, the hog badger is perhaps the most threatened, due to primarily to over-hunting - its apparently considered a delicacy in some parts of Laos. Having said that, across the broad expanse of its range, it lives in many protected habitats, and is specifically a protected species in many countries. Hog badger populations overall are declining, but, for the moment, seem high enough for at least their medium-term future to be secure.

[Images by 'Kallerna' and 'Nzrst1jx', from Wikimedia Commons. Cladogram adapted from Koepfli et al. 2008.]