Wednesday, March 20, 2013

Of shrews and owls

What: On Saturday Nathan and I went for a wander in Centennial Woods. We were exploring the lower stretches of Centennial Brook in Fox Marsh when we heard some crows making a ruckus to our East. We decided to track down the birds and see what the fuss was all about. Turns out the crows were harassing a barred owl that seemed more interested in napping than paying attention to the crows. After about 15 minutes the crows left the owl at peace. It was interesting to watch the owl over then next 45 minutes or so because any time a crow flew nearby it would caw, just to remind the owl they knew it was there. We walked back to my house to get better binoculars and my camera and the owl was still there by the time we got back. I snapped a couple of pictures of the owl perched near the top of an old white pine.

Short-tailed shrew skull found in barred owl pellet
Ecological notes: I've found a few owl pellets recently, (coincidentally?) all at the base of old white pines. The last one I pried apart was on the small end of pellets, but still had one vole and one shrew skull in it. The shrew skull was beautiful - I've always been drawn to the purple on the enamel of the teeth (as in rodents, the color is due to an iron pigment). Rodents have iron pigments on their incisors and softer exposed dentine (our dentine is hidden beneath our enamel) to maintain a sharp chisel edge. Anemic rats have been found to lack the pigmentation on their incisors! Older scientific articles speculated that the coloration could have been used as a signal (making the teeth visible when the animal grins aggressively). I doubt that, as white is equally visible. In shrews, it could signal health (redder teeth means more virility, as red feathers indicate virility in male cardinals, flamingos, etc).

Challenge: Find its eyes (or ears)!
I'd put more money on it being an architectural thing, increasing the strength of the teeth. Shrews are insectivores (in the order Insectivora, along with moles, neither of which are related to rodents; rodents, in fact, are closer to humans than shrews; shrews are closer to elephants than rodents like voles). Their diet consists primarily of arthropods (those six-legged bugs), which have hard shells. If you ate nothing but crab and had to chew through their shells with your teeth you could imagine your teeth would wear down pretty quickly. Reinforced teeth help their teeth last longer, though most shrews don't live past a year. Mira also found a short-tailed shrew (Blarina brevicauda) in Centennial Woods last week, which would be about the 6th this winter that showed no outward sign of any trauma.

Right front of short-tailed shrew

Rear feet of short-tailed shrew

Some observations we made about the shrew:
  • They have super short hair that rubs well both forward and back (possibly for entering unknown tunnels in search of prey)
  • They have large ear openings, but the external ear itself is super small
  • Their eyes are all but absent
  • Their whiskers are very prominent up the snout
  • The snout seemed to have the same reddish purple color that the teeth have
  • Their claws were exceptionally long
Where: Centennial Woods

Other notes: Almost exactly a year ago I spotted a barred owl in the same spot in the same way. I had actually followed the crows to a nearby spot where they were mobbing a red-tailed hawk.

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