Baby skunks and the evolution of stink

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Each spring female striped skunks will begin searching for the perfect hole.  They will look under decks, in culverts, and in the burrows of woodchucks, foxes, and even muskrats or badgers.  If they can’t find what they are looking for they will dig their own burrow, excavating a tunnel around 5 feet long and lining the chamber of the den with soft grasses and leaves for a comfy mattress.  Even with all this activity, female skunks will do their best to keep their search and their chosen burrow a secret.  Why all this trouble to avoid drawing attention?

This perfect hole is the den where a female skunk will give birth to her litter, a bundle of 5-10 blind and hairless baby skunks whose black and white skin tones are a preview of the distinctive black and white striped fur to come.  Unlike adult skunks that easily defend themselves from predators using their devastatingly stinky anal spray, baby skunks are defenseless. Any predator that finds a skunk den can quickly make a snack of the skunk babies, and male skunks also enter dens and kill and eat young.  A female with young in a den will aggressively fight off male skunks and vigorously defend the burrow and young from predators, often to the dismay of a coyote or bobcat that has been temporarily blinded by the spray of the mother.  The transformation from docile skunk to protective mother happens about a week before giving birth, and woe to the animal that provokes her at this time.  By the time the young skunks are 8 days old they can emit musk, but they are unable to defend themselves by spraying musk spray until they are about a month old.

Once skunks become adults they have little to fear from other animals. The musk that skunks spray from highly developed anal glands is such an effective defense that adult skunks are rarely killed by predators, although they are occasionally eaten as a last resort by foxes, coyotes, bobcats, or mountain lions. Great horned owls also prey on skunks, and since they have little sense of smell and are also nocturnal they may pose the greatest risk to skunks, but the threat is still relatively small.

Outside of the birthing season female skunks are happy-go-lucky animals that go about their nightly lives mostly oblivious to other animals.  The only time skunks appear to even pay attention to a person or animal is if they feel threatened, when they will begin a typical set of behaviors that progress from hissing while arching their back and displaying their tail, to stomping their front feet, and ultimately bending in a U-shape to simultaneously look at the threat and aim the business end of their musk glands before spraying.  While this strategy is remarkably ineffective against cars, it will drive off other animals and skunks will even chase after fleeing intruders.  Since the top running speed of a skunk is similar to the running speed of a frightened person this can lead to some heart-pounding nighttime encounters!

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Skunks are the only mid-Atlantic species that have this particular defense, but this ability has evolved multiple times in several different species around the world.  In a fascinating display of what is known as convergent evolution, or the evolution of similar attributes in different species groups, all of these species share common traits.   Species that spray anal musk for defense are mid-sized (compared to other carnivores), have black and white markings, are typically nocturnal, use open habitats, and are often stocky animals that do not run fast.  The bold black and white striping stands out well even at night, warning potential predators at any time of day.

The hard question is which came first?  Did skunks and other species evolve their effective musk defense and then start using open meadows and slowly evolve to be stockier and slower because they were less at risk of predation? Or did they evolve more musk production and the spray defense after their use of open habitats and slow, stocky bodies made them easy pickings for predators? This is the kind of interesting question that drives scientists to do what they do, but we understand if it is the last thing on your mind if you trip over an aggressive female skunk some spring night in the future!

For more information and pictures of striped skunks see:

Encyclopedia of Life

ARKive (pictures only)

Sources

Elbroch, M. and K. Rinehart. Behavior of North American Mammals.  New York: Houghton Mifflin,  2011. 374 pgs.

Stankowich T.S., T. Caro, and M. Cox. 2011.  Bold coloration and the evolution of aposematism in terrestrial carnivores. Evolution. 65(11): 3090-3099.

Wade-Smith, J. and B. J. Verts. 1982. Mephitis mephitis. Mammalian Species. 173:1-7.

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