Friday, June 24, 2016

Maryland: Weird and Wonderful - The Mystery of The Dead Shrews

Anyone who spends time outdoors in Maryland is bound to come across dead animals from time to time.  After all, one of the tragic but necessary qualities of life is that which lives also dies. With nature being the harsh mistress that she is, many animals fall victim to predation, starvation, disease, competition, and natural disasters.  It is not unusual to find the remains of wildlife past as we explore our parks, gardens, and neighborhoods.

However, one diminutive creature's remains hold an air of mystique to those who find them.  The bodies of shrews are often found completely untouched in the middle of trails and walkways. It's as if in the midst of crossing, the small animals simply dropped dead.  Often mistaken for mice or voles by those who find them, shrews are not rodents, but are more closely related to hedgehogs and moles.  Shrews can easily be told from mice and voles by their exceptionally pointed snouts and sharp, red teeth.

A dead, yet untouched, shrew. 
Shrews' lives can be claimed in many ways.  Being small but active animals, they have a high metabolism and need a steady supply of food to drive it.  During population bursts, it is possible that some shrews may starve for lack of food.  Fights with rivals in order to secure good feeding and breeding grounds may also take their toll. It is even possible that the furiously whirring organs of shrews cannot handle excess stress, and they may die if overly exerted. Further, shrews have remarkably short natural life spans, only 1-3 years.  Factor in parasites and disease, and it seems the Grim Reaper is constantly nipping at shrews' tiny heels.

However, shrews who meet their ends in these ways typically die where they live - beneath the cover of overgrowth and leaf litter, not out in the middle of trails and sidewalks. What is compelling shrews to keel over in such unusual, exposed places?

The answer lies in the shrews' defense mechanism. Many shrews, including our most common shrew, the northern short-tailed shrew (Blarina brevicauda), have a secret weapon - an unpalatable stench and taste exuded from glands on their bellies and sides.  This makes them exceptionally distasteful to scent-oriented predators, such as foxes, weasels, and roaming cats. The shrews' frantic scurrying beneath the leaves is irresistible to such predators, who probably mistake the small mammal for something tasty, like a mouse or vole. Once caught and killed with a bite or shake, it becomes apparent that this little creature is absolutely foul, and its virtually unscathed body is discarded.

Foxes and cats may not like shrews, but scavengers, such as flies and beetles, don't mind the smell!
Foxes and cats often use established trails, including human pathways, as it is easier than bushwhacking and it gives them the best opportunity to smell the markings left by animal and human traffic through the day.  The unwanted bodies of shrews are left by the wayside of these predator highways, some even surrounded by scrape marks or feces, essentially "put out with the trash." Domestic cats who are allowed to roam may leave shrews as "gifts" for their owners (or other friends), in which case, they are often left in conspicuous places, such as doorsteps or even their humans' beds!

Shrews do have predators that eat them, namely owls, which do not seem bothered by their noxious smell.  However, owls tend to swallow their prey whole and leave no carcass, which adds to the rarity of half-eaten or badly mauled shrews.

If you find a dead shrew on your property, take it as a bit of useful information! Here are a few things you can surmise:

  • You have shrew food on your property, which may include worms, beetles, slugs, mice, and small snakes.
  • If you don't like worms, beetles, slugs, mice, or small snakes, you are in luck! You have shrews eating them.
  • You have predators that don't like to eat shrews on your property, probably foxes or domestic cats.
  • You have good shrew habitat, including leaf litter and overgrowth, which is also great habitat for many other creatures, such as frogs and fireflies.
  • You may also have moles, since shrews frequently use old mole tunnels as they forage. 

So what can you do with this information?

  • For starters, don't let your cats outside! Shrews eat pest animals and owls love to eat shrews.  You can help feed owls and control pests by keeping cats away from shrews. Also, cats allowed to roam outside are at higher risk of killing other beneficial wildlife, as well as getting killed themselves!
  • You are doing a good job at creating good wildlife habitat on your property - keep it up! Replace some of your lawn with gardens, and don't worry too much about those mole hills. 

REFERENCES:

Animal Diversity Web, University of Michigan
http://animaldiversity.org/

Internet Center for Wildlife Damage Management, "Shrews"
http://icwdm.org/handbook/mammals/shrews.asp

Maryland Biodiversity Project
http://www.marylandbiodiversity.com/


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