Saturday, December 13, 2008

The facts, just the facts, Mam!

Continued from "The Corpse in the Garage"

The Body:
total length 3 3/4 inches, body length 2 1/18 inches, tail length 5/8 inch, forefoot length 3/8 inch (without nails), hind foot length (without nails) 9/16 inch

The shrew I found in the garage was tiny, if you have never seen one, it is apparent from my measurements that they are quite small. Since his tail is only slightly longer than his back foot, he is a short-tailed shrew. In the southeast, there are several short-tailed shrews. There is the least shrew (Cryptotis parva), but they are very small and distinctly bicolor. My guy is not like that. The other short-tailed shrews are in the Blarina species. There are three or four Blarinas depending if you are a taxonomic lumper or splitter: northern short-tailed shrew (Blarina brevicauda), southern short-tailed shrew (Blarina carolinensis), Elliot's short-tailed shrew (Blarina hylophaga), and Everglade short-tailed shrew (Blarina peninsulae) as a species if you are a splitter, or Blarina brevicada peninsulae as a subspecies if you are a lumper. In north Alabama, it is simplified somewhat in that only the northern and southern might be found here. Note I said, "might be." Range maps are all over the place, and the only consistency in the maps is their inconsistency. So, I do not know whether the shrew is a northern or a southern short-tailed shrew.

What are the differences between the northern and southern? Minor, and somewhat esoteric, skull differences are found and to some degree, size. The best detectable difference is chromosomal count, but as far as I can tell, there has been no comprehensive genetic study of short-tailed shrew distributions in Alabama. In "Mammalian Species," published by the American Society of Mammalogists, the southern short-tailed shrew appears to occur below the Tennessee River in this area, and the northern short-tailed shrew appears to be above the Tennessee River. So, by that, it would probably be the northern, but not so fast! "Mammalian Species'" authors report that the total length of northern short-tailed shrews as ranging from 106-126 mm in Pennsylvania to 125-141 in Nebraska. For southern short - tailed shrews, the authors give sizes in several southern states: 72-95 mm in Louisiana, 99-105 mm in South Carolina, 90-105 in Kentucky, 84-102 mm in Florida. these measurements my shrew (95mm) is a southern short-tailed shrew. To confuse it more Schwartz and Schwartz in Wild Mammals of Missouri report these total length ranges: northern 95-127 mm (3 3/4 -5 inches) and southern 72-107 mm (2 3/4- 4 1/4 inches). So you can see there is size over lap between these species. The Schwartzes, appearing to follow Brown's distributions in the south from his book, A Guide to the Mammals of the Southeastern United States, show that southerns are the only inhabitant of north Alabama. Befuddled and not amused I do not know what my poor deceased shrew’s identity.

So, not knowing what shrew it was, I thought I would consult the authorities, and I whipped off an email to the Anniston Museum of Natural History:

“I am trying to find out what short-tailed shrews live in north Alabama. Range maps I've found are contradictory; some report the northern and some report the southern short-tailed shrew, but none report overlap in ranges.”

I promptly received an answer back from Dr. D. Spaulding, Curator of Collections. He sent me an Alabama mammalian land species list and neatly side stepped the question:

“I have attached a list of all the Land Mammals of Alabama. We have 4 species of shrews in Alabama.”

His answer or lack of answer tells me volumes...that there is probably not a definitive answer without genetic studies. So I do not know what kind of short-tailed shrew it is (I’m leaning to southern, but what do I know).

Next, what is its gender? I've been calling it a he, but I really do not know its gender. These shrews do not have an external scrotum as the testes are housed internally in the body, a primitive feature. The birth canal of the female is not a separate external opening. A shrew is a primitive mammal and has a cloaca, the external opening, into which the urinary, intestinal, and reproductive tracts empty. So there is no obvious external gender difference. There are minor size differences reported between males and females, but that is relative and not a definitive marker.

So what do I know? The shrew is small, it is either a northern or southern short-tailed shrew, its gender is unknown, and it died from undetermined causes. I would make a poor policewoman! I am not the only one lacking the facts, science know very little about these shrews. Their semi-fossorial (semi-burrowing) lifestyle along with that they do not reliably enter into traps makes them difficult to study.

Why care about a small mammal such as the shrew that you may never see, well...Jackson in his book Mammals of Wisconsin did the math:

Assuming that each individual consumes an average of about one-third its own weight each day (eight grams), the army of 84 million mole shrews [his name for short-tailed shrews] in Wisconsin consumes more than 500 million tons of pests annually, and equivalent of two big truck loads a day for each county in the state. If we assume that each Blarina averages less than three invertebrates (insects, snails) a day and less than two mice a year then numbers consumed would reach the almost unbelievable, yet not unlikely, number of 90 billion invertebrates and 150 million mice...The mole shrew must be accepted in the class of mammals as a very useful ally to man.

Just think, without shrews in your yard you might be overrun with roly-polys!

Later what is known of the cool natural history of short-tailed shrews...

Pam Croom © 2008

References used in "The Corpse in the Garage" and "The Facts, Just the Facts, Mam"

Brown, L.N. 1997. A Guide to the Mammals of the Southeastern United States. The University of Tennessee Press. Knoxville. 236pp.

Chapman, S. 1990. The Natural History of Shrews. The Natural History of Mammals Series. Comstock Pub. Assoc. Cornell University Press. Ithaca. NY. 178pp.

Choate, J.R., J.K. Jones, Jr., and C Jones. 1994. Handbook of Mammals of the South-Central States. Louisiana State University Press. Baton Rouge. 300pp.

Fry, B. G., The Poisonous Primate?!, accessed 12/3/08

George, S.B., J.R. Choate, and H.H.Genoways. 1986. Mammalian Species. 261: 1-9

Jackson, H.H.T. 1961. Mammals of Wisconsin. The University of Wisconsin Press. Madison. 504pp.

McCay, T.S. 2001. Blarina carolinensis. Mammalian Species. 673: 1-7

Pepling, R. S. 2004. Critter Chemistry: The Stunning Saliva Of Shrews, Researchers are trying to unravel the mystery of the shrew's venomous brew. Chemical & Engineering News. accessed 12/3/2008

Schwartz, C.W. and E.R. Schwartz. 2001. The Wild Mammals of Missouri. University of Missouri Press. Columbia. 2nd re. ed. 368pp.


Gerritnow said...

Hey, I love your photos..they are really nice...

Pam Croom said...

Thanks for visiting!

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