Sunday, September 4, 2011
The Showtl's Underworld, Part 4
Can you see the bristles on its hind feet?
Well, neither can I.
Bristled feet are a diagnostic characteristic of the world's smallest diving mammal -- the American water shrew.
The photo doesn't do justice to the shrew's hairy feet, but that doesn't mean it isn't Sorex palustris.
It matches the other external features.
Water shrews look like miniature torpedoes when they dive for amphibians, fish and aquatic insects in fast-flowing streams, and they do it all while dog paddling and twirling their tails like propellers.
Shrews (and especially shrews of the red-toothed tribe or Soricinae) live in the fast lane, pushing the envelope of energetic possibility.
They have relatively high thermal conductance, which means they are not well insulated, but their compensation for this deficiency is a high basal metabolic rate (BMR) and high body temperature (38.6 degrees C = 101.3 F).
Thus, shrews are fascinating topics of investigation, but as subjects of energetic study they are frustrating in the extreme.
Within the physiologist's metabolic chamber or respirometer, research subjects are supposed to rest peacefully in a state of post prandial quietude as the equipment measures their oxygen consumption and carbon dioxide production.
And they should also be "postabsorptive" -- not digesting food -- because digestion has a caloric cost and raises metabolism.
Shrews are not good at this, because they are fussbudgets around the clock and they rest only briefly.
Their basal metabolic rate is so high, that the time it takes for food to pass through the digestive system ('throughput" to physiologists, "poop time" to most readers) is about an hour.
Count yourself blessed if you ever see a water shrew.
You have seen a rare sight -- the world's smallest diver, and one of the faster poopers in the west.
Question: the practitioners of what outdoor recreation have the best chance of seeing water shrews?
Post you answer in the comment section, and speak up if you yourself have seen one in action.
Gusztak, R.W. , R.A. MacArthur, and K.L. Campbell. 2005. Bioenergetics and thermal physiology of American water shrews (Sorex palustris). Journal of Comparative Physiology, 175:87-95.