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Friday, July 12, 2013

A New Look At Skunks

A New Look At Skunks

Few mammals are more easily recognized than the striped skunk (Mephites mephitis).  The species is prominent in children’s books, cartoons and movies and many are seen dead along highways.  But much of what we’ve been told about the odiferous, cat-sized animal with the ultra-familiar white stripe on a black body is myth, or at least, not quite correct. 

Authors of books on mammals have long-considered all four North American skunks – the striped skunk, spotted skunk (Spilogale putorius), hooded skunk (Mephites macroura), and hognose skunk (Conepatus leuconotus) – as members of the weasel family (Mustelidae).  But genetic research by evolutionary biologist, Jerry Drague, and others has revealed that skunks have much different chromosomes and proteins than weasels and should be classed in their own family (Mephidae).  Although weasels use odor to mark territories and some, like mink, even use scent to repel other species, skunks take it to a whole other level.  Skunks have also evolved some behaviors not shared by any of the weasels.

Only the striped skunk is found in Michigan.  Its range includes almost all of the U.S., except Alaska, and extends north to the boreal forest of Canada and south well into Mexico.  The spotted skunk also has a wide range, but is not found as far north or east.  The spotted skunk does well in prairie habitat, even in the cold climates of Wyoming, the Dakotas, Minnesota and Wisconsin.    And unlike the other skunks, it can climb and feed in trees on birds’ eggs and smaller mammals.  The hooded and hognose skunks are confined to the southwestern U.S. and Mexico.

The striped skunk is nocturnal, but occasionally moves about in daylight.  It feeds on almost anything from small animals to eggs to dead carcasses and garbage.  It is a highly-skilled predator of mice and voles, on a par with foxes and cats in catching small rodents in grassy areas.  The striped skunk uses a set of burrows and dens, often returning to several spread out along a route that may be 15 miles long.  A skunk typically travels about three miles a night during feeding, but that varies greatly depending on the terrain and food availability.

The males tend to be solitary, but female skunks sometimes den together, especially in the winter in cold climates to share body warmth.  Striped skunks don’t hibernate, but may stay underground for several days during harsh winter weather.  Mating typically occurs in February or March with young born temporarily blind in May.  Litter size varies widely – usually four to six – but with as many as 10 occasionally recorded.  This prolific reproductive rate can lead to populations of up to 60 skunks per square mile in some areas.  Some of the highest skunk populations occur in urban/suburban areas where skunks take cat food off of porches and garbage from dumpsters by night and hole up under abandoned buildings by day.

One study found that skunks and cats can be surprisingly tolerant of each other, often sharing resting and feeding areas.  The normal reaction of skunks to larger animals, however, is to threaten chemical warfare.  The striped skunk employs a series of tactics and warning gestures before it gets down to the business of spraying a would-be predator.  First, it tries to walk or run away; this is followed by a backwards shuffle if forced to face the threat.  Next, the skunk often stomps its front feet up and down.  When a quick escape seems unlikely, the skunk elevates its tail to show as much of its white stripe as possible.  (The spotted skunk will actually do a very impressive hand-stand with its rear and tail high in the air.  Yes, it can spray from that position!)  A predator with previous (and bad) skunk experience may remember the white warning signal.  If not, the skunk then releases as much as four tablespoons of a greenish liquid emitted from a nozzle-like structure.  It comes out as a mist that looks yellowish as it travels through the air.  It was evolved to irritate the odor-sensing system of many of the skunk’s potential predators.  It works on most (see accompanying story on the next page), but one important predator of skunks not effected much by the spray is the great horned owl.  It has a very poorly developed sense of smell and its eyes aren’t irritated by the chemical.

Researchers have also discovered that some people are much less susceptible to skunk spray than others.  There are individuals who can be sprayed at close range with very limited reaction.  Researchers comparing sprays in laboratories have found that spotted skunk spray tends to smell “sweeter” than that of striped skunk, at least to most people.

After a skunk sprays, it takes several days for it to replenish its supply.  The skunk apparently can’t tell when it carries enough chemical for an effective defense.  So, the evolution of the series of warning gestures is very important for survival of skunks that are temporarily “unloaded.”  The skunk carries out the same gestures regardless if the chemical is present.  If there is none, and the predator does not fall for the “bluff,” the skunk gets eaten. 

Skunks take a toll on both eggs and newly-hatched young of ground-nesting song birds, pheasants and quail, but also reduce numbers of small rodents, snakes, and harmful insects.  They raid poultry houses, but take fewer eggs and chickens than other common predators.  They do sometimes carry rabies – ranking second to raccoons among mammal carriers of the dreaded disease.

Many people have de-scented or ranch-raised skunks as pets.  The latter are often all-white or blonde.  Some skunk owners find them delightful, but most people aren’t willing to provide the care skunks require.  It is illegal and otherwise highly inadvisable to capture and keep a skunk found in the wild.

Dr. Patrick Rusz
Director of Wildlife Programs

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