Identifying an unknown Shrew
Jamie, a parent of one of the kids at The Guelph Outdoor School where I work wrote to me recently, sharing some photos of a dead Shrew she had found at one of my favorite places near to where I live. She guessed it could be a Pygmy Shrew (Sorex hoyi) and asked what I thought. I looked at her photos, one without and one with scale (a larger Bic brand lighter measuring 80mm long). This is a great start for identifying stuff from photos. It is always good to include common objects for scale, like a lighter, some keys, or a coin (I prefer canadian quarters which are 23.88 mm in diameter, with each letter in the word C-A-N-A-D-A approximately 2 mm wide). I followed up by asking if she had collected the animal and if she could bring it to me to the next day to take good measurements and some photos. Jamie wrote back that she had not collected the animal but that she would take measurements in the field from now on, which is great. I appreciate that kind of follow through.
Next day, I am walking out to meet my students, and there Jamie was waving with something in her other hand. Turns out she and her child went out that morning to collect the Shrew and bring them in so we could take a look with the kids and I could take some measurements. What a gift!
When I got the chance during my sit spot in the morning I took some time to really examine the animal. How do I know that this was a Shrew anyways, and not a some local Mouse (Peromyscus spp.) species? First I checked out the animals head. The three common Mice species that I might come across this time of year, Deer Mouse (Peromyscus maniculatus), White-footed Mouse (Peromyscus leucopus), or a House Mouse (Mus musculus) that ended up out in the woods somehow, all have comparatively large black eyes, while this animal has tiny little beads of black. The mice would also have large ears, while this animal’s ears are even harder to notice than their eyes. Next I can look to the feet and the number of toes. Mice are rodents, and all of the rodents in our area have 4 toes on the front feet, and 5 on the hind feet. This animal had 5 toes on the front feet and 5 toes on the hinds. With these very simple and quick i.d. features I could tell that this was not a mouse, not even a rodent. All that this could leave, based on size, habitat, commonality of species, would be one of the smaller Shrews (Sorex spp.).
Between trying to take quick photos of the Black-capped Chickadees (Poecile atricapilus) flying in to grab some Sunflower (Helianthus annuus) seed I put out, I grabbed my tape measure and jotted some measurements down.
The measurements for the Shrew Jamie found:
Entire Length (EL) : 90 mm
Tail Length (TL) : 38 - 39 mm
Hind Foot Length (HFL) : 10 - 11 mm
Throughout the day I tried to show everyone the dead Shrew. I asked them who they thought it was and commonly I heard Mouse, Rat (Rattus rattus), Meadow Vole (Microtus pennsylvanicus), Mole (Talpidae family) but very few said Shrew. This was a reminder and reinvigoration of my commitment to popularize understandings of Shrews in my broad communities. Many of the children we interested, some even ventured to pet the Shrew. One child asked if they could take them home. I let everyone know they were coming home with me for a photo shoot and some more measurements.
When I did get home I also weighed the Shrew, (along with some coins for comparison) to help distinguish species. Here’s what I got:
Shrew : 4.1 g
Canadian Quarter : 5.8 g
Canadian Dime : 2.3 g
When I held the Shrew in my hand, I could tell they were a bit lighter than a quarter but I couldn’t really tell by how much. Even though I could feel the difference when I held the Shrew, I was still surprised by the difference compared to the quarter when I read it on the scale. I then began the process of looking up the measurements and weights. This was a simple task due to Donna Naughton’s 2012 tome The Natural History of Canadian Mammals, which conveniently had all of the measurements and weights for each of the possible local Shrew species. Because I knew it was not the Short-tailed Shrew (Blarina brevicauda), or the Northern Water Shrew (Sorex palustris), I didn’t even check their numbers. This individual had a longer tail than the Short-tailed and was much smaller in overall size than the Water Shrew would be. I also didn’t look up the Least Shrew (Cryptotis parvus), because I knew this species has only been documented in Ontario at Long Point. I did look up Masked/Common/Cinereus Shrew (Sorex cinereus) as the one Jamie had found looked similar to previous Cinereus Shrews I had found in the past. I also looked up Pygmy Shrew (Sorex hoyi), and Smokey Shrew (Sorex fumeus). I also decided to look up habitat for each of the latter three species to see if they may occupy different terrain and thereby be able to further clue in on the individual and species that Jamie found.
Found Shrew :
Entire Length : 90 mm
Tail Length : 38 - 39 mm
Hind Foot Length : 10 - 11 mm
Weight : 4.1 g
Habitat : Found dead along open trail with mature trees beside.
Pygmy Shrew :
EL : 62 - 104
TL : 22 - 35
HFL : 6 - 12
Weight : 2.1 - 5.3 g
Habitat : Wooded areas (both coniferous and deciduous), bogs, wet meadows.
Cinereus Shrew :
EL : 75 - 125 mm
TL : 28 - 50 mm
HFL : 8 - 14 mm
Weight : 2.2 - 8 g (avg 3.6 - 4.6 g)
Habitat : Margins of moist fields, bogs, marshes, moist or dry woods and brushland.
Smokey Shrew :
EL : 104 - 125 mm
TL : 42 - 54 mm
HFL : 12 - 15 mm
Weight : 5.8 - 8 g
Habitat : Moist leaf litter, and rotten logs in mature deciduous or mixed woods.
Otherwise these Shrews can look very similar. When the numbers overlap with a few different species, you may have to look at their upper teeth under magnification to tell them apart. The little usb microscope thing I have wouldn’t be that powerful to see the variations in the teeth, but I hope to be able to acquire a better, more powerful microscope someday. Until then I’ll rely on the measurements, weights and habitats.
The unknown Shrew has an overlapping entire length, hind foot length and weight with Pygmy Shrew, but nothing overlapping with the Smokey though close on tail length and hind foot length. When compared with the Cinereus Shrew, the found Shrew fits in with all criteria - measurements, weight, and habitat. This would suggest that the found Shrew is a Cinereus Shrew. That would make sense as they do look similar in size, and weigh similarly to previous Cinereus Shrews I have found dead along the sides of trails.
How did they die? I don’t know but Jamie was thinking perhaps a domestic Dog (Canis familiaris) had found them and killed them. For now, the Cinereus Shrew will go into my freezer so I can place them outside when it warms up and see if I can lure any Carrion Beetles in my yard to observe and photograph.
Big thanks to Jamie for sharing this awesome find, and to the Shrews who keep on doing their Shrew thing unbeknownst to us humans.
To learn more :
The Natural History of Canadian Mammals by Donna Naughton. University of Toronto Press, 2012.
Mammals of the Canadian Wild by Adrian Forsyth. Camden House, 1985.