Indeed, sables and pine martens still look very similar, although the former have shorter tails, and the 'bib' on their chests is usually less distinct, varying from pale brown to yellowish. Their fur is rich and luxurious, especially during the winter months, and can be anything from pale brown to the near-black colour for which they are most famous. Largely on the basis of this variation in colour, up to thirty different subspecies have been identified, although, personally, I suspect that the animal is just rather variable in appearance, and many of these subspecies won't turn out to be valid under more thorough investigation.
Like pine martens, sables inhabit both deciduous and coniferous forest, although they prefer the latter. They were once found across the vast forests of Siberia, into Mongolia and northern China, and, even today, they inhabit the islands of Hokkaido and Sakhalin either side of the Japanese/Russian border. They can, of course, climb trees, but they seem to do so less than pine martens do, and they make their homes in underground burrows, sometimes of considerable length, with entrances partially concealed beneath tree roots or similar cover.
Like other martens, they are generally solitary, although males and females don't mind sharing the same area. Indeed, in Hokkaido, they seem remarkably tolerant of each other, perhaps because there is plenty of food but, it being an island, relatively little space to inhabit. However, they are not particularly attached to their homes, and, if times are bad, they will travel many miles to seek out fresh pastures. They are mostly carnivorous, feeding mainly on rodents, although any meat will do in a pinch, and they will eat berries and the like when nothing else is available.
Also like pine martens, they breed in the summer, but do not give birth until the following spring, generally producing a litter of three or four young, which will be weaned by the time the breeding season rolls around once more. They are, for the most part, crepuscular, but will happily switch to nocturnal or daytime activity, depending on their circumstances, or even the time of year.
Sables are most famous for their fur, which remains among the most valuable of any animal. By extension, the word 'sable' has come to refer to black fur in general, whether of breeds of rabbit or other domestic animals, or of species of antelope. Up until the mid twentieth century, sable populations suffered from hunting, and today, there are wide stretches of Siberia where they no longer live, and they are all but extirpated from China. As fur farming became more popular in Russia, they recovered, and wild sables are no longer under threat.
Fur farming itself is not without its problems, since most wild sables are not the near-black colour that is in most demand commercially. Attempting to breed for this valuable colour is certainly successful, but it does result in a restricted gene pool, and a general loss in female fertility.
Japanese martens, which also live in Korea, are physically very similar to their American cousins, which is to say, slightly smaller and slimmer than the pine martens and sables. They tend to be slightly paler, too, and, while they can be dark brown, many are yellowish, with a near-white bib. While American martens are restricted to pine forests, the Japanese species inhabits broadleaf forests around the central mountains, where they nest in either trees or burrows. They are apparently nocturnal, and eat a high proportion of insects and other invertebrates, as well as the more usual rodents, but we know surprisingly little else about them.
Like other martens, they are hunted for their fur, although today the Japanese government imposes a strict hunting season during the winter, and has established a couple of protected areas, including one for a threatened subspecies on Tsushima Island. Neither of the other subspecies (there's one each in Japan and Korea) appear under any threat, however, and they are apparently more at risk from road accidents and attacks by feral dogs than they are from deliberate hunting.
Korea is also home to the yellow-throated marten (Martes flavigula), which also inhabits nearby Manchuria. This northern subspecies, however, is somewhat isolated from other yellow-throated martens, most of which live further south. They are found through much of central, southern, and eastern China, south of the Himalayas in India, Bhutan, and Bangladesh and across South-east Asia, as far as the islands of Borneo and Sumatra. A subspecies on Java is endangered, but they seem safe enough across most of their range. That may well be because their fur is too coarse to be valuable, although they are frequently eaten in Taiwan.
Somewhat unusually, they appear fairly sociable with others of their kind, and hunt in pairs, or small family groups. They breed around August, at least in some parts of their range, and give birth in the spring.
The least known of all the martens is the Nilgiri marten (Martes gwatkinsii), which is found only on the forested slopes of the Nilgiri hills in southwest India. So similar is it in appearance to the yellow-throated marten, that some authors have considered them to be the same species. From what little we know, it has much the same lifestyle as its slightly larger and more widely distributed cousin, and it is considered a vulnerable, though not endangered, species, as much due to the advance of local agriculture as anything else.
The fisher (Martes pennanti) is probably not a true marten, although it is certainly a close relative. It lives in a relatively narrow band of territory either side of the US/Canadian border, and also down into California, where it inhabits dense forest with heavy cover. While perfectly capable of climbing trees, they spend more time on the ground than any other marten, and they are mainly crepuscular, although they can be active at any time of day or night. Fishers create no permanent dens, simply borrowing hollow trees or brush piles for a night or so at a time.
They corner the porcupines on the ground, sometimes after chasing them down from a tree, warily circling them and making sudden lunges at the animal's face - the only area that doesn't have heavy protective spines. This can continue for up to half an hour, with the porcupine constantly trying to present its spiky rear end to the fisher, and the fisher trying to get round to the front. Eventually, if the fisher is lucky, the porcupine succumbs to its wounds, and can be safely flipped over on to its back before feeding.
Aside from their propensity for hunting on the ground, the social life of fishers is much the same as that of any other marten. With delayed implantation, gestation lasts almost a full year, with the female mating again just ten days after giving birth - meaning that she must spend almost her entire adult life pregnant.
Like so many other members of the weasel family, fishers have been hunted extensively for their pelts. So much so that, by the mid twentieth century, they had been almost entirely wiped out in the US, although they fared somewhat better in Canada. There is some evidence that the population of porcupines rocketed as the fishers died off in their native lands, but something closer to a normal balance has been restored since, with the species being re-introduced to a swathe of states across northern and western America. In places such as Oregon, fisher populations are still suffering from this past destruction, but, as a whole, the species is no longer at risk.
[Sable image from China Wildlife Conservation, Japanese and yellow-throated martens by "Gin Tonic" and "Altaileopard" from Wikimedia Commons, fisher by John Jacobsen, from the US Fish & Wildlife Service. Cladogram adapted from Koepfli et al. 2008.]