Taxonomy and Systematics
Dragoo (2009) recognized two subfamilies within the family Mephitidae. One subfamily, Myadinae, includes the two species of Mydaus stink badgers. In the other subfamily, Mephitinae, Dragoo recognized 10 skunk species in three genera: Conepatus, Mephitis, and Spilogale. Dragoo noted that the number of species recognized will likely change as revisions are undertaken using modern methods such as molecular phylogenetic analysis. However, as of 2009, he recognized the following six genera and twelve species of mephitids:
Mydaus (2 species): Sunda Stink Badger (Mydaus javanensis), from Java, Sumatra, and Borneo (the Greater Sunda Islands), and Palawan Stink Badger (M. marchei), from the island of Palawan in the Philippines. These two species were at one time placed in two separate monotypic genera, the Palawan Stink Badger being placed in a genus Suillotaxus.
Conepatus (4 species [now 3?]): American Hog-nosed Skunk (Conepatus leuconotus), from the southwestern United States south to Nicaragua; Molina's Hog-nosed Skunk (C. chinga), from Peru to Chile, Argentina, and southeastern Brazil; Striped Hog-nosed Skunk (C. semistriatus), with an apparently disjunct distribution from southeastern Mexico to Colombia and Venezuela and northeastern and central Brazil; and Humboldt's Hog-nosed Skunk (C. humboldtii), from Chile and Argentina. Schiaffini et al. (2013) analyzed morphometric and mitochondrial DNA variation and concluded that C. chinga and C. humboldtii are actually conspecific (i.e., belong to the same species) and that environmental variation seems to be responsible for shape and size variation in Conepatus skulls from southern South America. Thus, they considered all the skunks of southern South America (Uruguay, central and southern Chile, and Argentina) to belong to a single species, C. chinga. Similar analyses previously resulted in the collapsing of the putative species C. mesoleucus ("Western Hog-nosed Skunk") into C. leuconotus ("Eastern Hog-nosed Skunk") (Dragoo et al. 2003).
Mephitis (2 species): Hooded Skunk (Mephitis macroura), found from the southwestern United States to Nicaragua, and Striped Skunk (M. mephitis), found across much of Canada and most of the United States south to northwestern Mexico.
Spilogale (4 species): Pygmy Spotted Skunk (Spilogale pygmaea), found in western Mexico; Eastern Spotted Skunk (S. putorius), found across much of the eastern and central United States; Western Spotted Skunk (S. gracilis), found in the western United States south to northern Mexico; and Southern Spotted Skunk (S. angustifrons), found from central Mexico south to Costa Rica. Although the Eastern and Western Spotted Skunks were long considered to belong to a single species, a variety of data suggests that they are at least largely reproductively isolated and should be recognized as distinct species (Kaplan and Mead 1994 and references therein; Kinlaw 1995 and references therein). Spotted skunks are the smallest of the skunks and are good climbers, able to move up and down tree trunks like squirrels.
Skunks are best known for their extremely enlarged scent glands (modified apocrine sweat glands) at the base of the tail, which they use to squirt a noxious fluid at potential predators. These enlarged scent glands are among the several features that were long considered to be shared with weasels, resulting in the skunks being included in the weasel family, Mustelidae. It is now clear, however, that at least some of the characters traditionally used to unite skunks and weasels are not actually shared, derived characters ("synapomorphies"), as is logically required if they are to be used as evidence that the two groups share a more recent common ancestor with each other than with other carnivorans (Dragoo and Honeycutt 1997 and references therein). Analysis of chromosomes also does not suggest a very close relationship between skunks and weasels. Molecular phylogenetic data have shed considerable light on the phylogenetic placement of the Mephitidae within the order Carnivora and consistently indicate that the skunks and mustelids are not actually closely related. As of 2013, it appears that Mephitidae is basal to a clade consisting of Ailuridae [Red Panda], Procyonidae [raccoons and allies], and Mustelidae, with Ailuridae basal to (Procyonidae + Mustelidae) (Dragoo and Honeycutt 1997 and references therein; Eizirik et al. 2010; Nyakatura and Bininda-Emonds 2012; Sato et al. 2012).
All skunks exhibit some degree of sexual dimorphism in skull morphology, but this is most evident in the spotted skunks. Male skunks have a baculum ("penis bone"), although it is smaller than it is in most carnivores, and females have an os clitoris. Dragoo (2009) reviewed the skeletal morphology of the skunks.
Skunks have been recorded from sea level to 4200 meters, but are more common at elevations below around 1800 meters. The family is distributed mainly in the New World, from Canada to Argentina, but the two species of stink badgers are found in the Philippines, Java, Borneo, and Sumatra. New World skunks are found in an extraordinary range of habitats, but generally not in the most arid and hot deserts of the southwestern United States or in arctic Canada (although there are, in fact, reports of Striped Skunks occurring north of the Arctic Circle). Northern Mexico and the southwestern United States have the highest skunk diversity, with three genera and five species, although typically no more than two species co-occur in the same habitat. Striped Skunks do well in urban areas, as do Hooded Skunks in the desert southwest of the United States. Even spotted and hog-nosed skunks may be adapting somewhat to living in urban areas. The only skunks in South America are the hog-nosed skunks, which are found in a wide range of mostly fairly open habitats. In their range in southeast Asia, stink badgers are found mainly in montane areas, although they have been found at lower elevations as well. They can occur in a range of open natural habitats, agricultural areas and secondary forest, as well as in the vicinity of human habitation.
Skunks are opportunistic and omnivorous in their feeding habits. All of them will eat insects, but insects tend to represent an especially large component of the diet for hog-nosed skunks. Hog-nosed skunks spend more time and energy digging for beetle grubs and other insect larvae than do other skunks, explaining the resemblance of their shoulder blades and humerus (upper forelimb bone) to those of American Badgers (Taxidea), which are also committed diggers. Like the nose of a hog, the nose of a hog-nosed skunk is hairless, flexible, and well suited for rooting for food. Stink badgers forage at night for worms and other invertebrates as well as eggs, carrion, and some plant matter. They are rather slow-moving animals with a top speed around that of a walking human.
Skunks dig holes in the ground or use burrows excavated by other animals. In warm weather, they will nest above ground under cover and some skunks (Hooded and spotted) will even nest in trees. They are generally nocturnal and solitary (although in very cold weather, females may den together, sometimes with a single male, to conserve body heat and body fat). Their natural predators include Coyotes, Bobcats, foxes, and owls.
Striped Skunks are known to be induced ovulators, shedding eggs within 40 to 50 hours of copulation. Dragoo (2009) reviewed the basic reproductive physiology of skunks.
A skunk's spray is a potent defense, but escape is generally a skunk's first choice when it encounters a perceived threat. If escape is not a feasible option, performing a threat display rather than actually spraying may be effective (stink badgers may play dead). If threatened, an American Hog-nosed Skunk can put on an impressive threat display, standing on its hind legs, then coming down on all fours, hissing and flinging dirt backwards and, eventually, stomping its front paws, raising its tail, baring its teeth, and spraying and biting. Depending on the circumstances, a skunk can spray either a cloud of fine mist or a narrow stream, often directed at the face, which can sting and temprarily blind a predator as well as overwhelm its olfactory system. Interestingly, a skunk is able to avoid spraying scent on its own body except for in exceptional circumstances, e.g., when it has been captured by a predator and is desperately trying to save itself or after being hit by a car.
In much of the world, domestic and feral dogs are the primary reservoirs and vectors for rabies. In the United States, however, extensive vaccination has shifted this status to wild mammals, especially carnivores. Prior to 1990, Striped Skunks accounted for the most cases of rabies reported in the United States, but after 1990 an increase in the prevalence of rabies among Northern Raccoons (Procyon lotor) bumped skunks to #2.
The populations of most skunk species seem currently to be relatively secure, at least on a global scale. The Pygmy Spotted Skunk, however, is listed on the IUCN Red List as Vulnerable. It has suffered from substantial habitat destruction across much of its range and in some places these animals are killed, stuffed, and sold as souvenirs. For skunks in general, the main threats seem to be hunting by humans and habitat loss. The Palawan Stink Badger is generally common, but may be vulnerable simply because its range is rather limited. The Eastern Spotted Skunk was once common throughout the midwestern and southeastern United States, with consistent annual range-wide harvests of >>100 000 animals. In the 1940s, however, populations crashed and the decline has continued more slowly in subsequent decades, although the cause of this decline is unclear. The species is currently listed by various state agencies as endangered, threatened, or "of concern"’ across much of its range. (Gompper and Hackett 2005)
(Dragoo 2009 and references therein)
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