Friday, February 13, 2009

Why birding is better, usually.

Because then you don't have to identify voles.

We found this fellow beside the trail at Terra Nova Rural Park today. He seemed a bit stunned; at first I thought he was neo-dead. But then he shuffled forward a bit.

What was it? Well, obviously a vole, but then what? I’m certain that if you were a small mammal biologist, you would instantly know what species it was. But if you aren't, well, you're in a world of uncertainty. There are few or no diagnostic features to differentiate among the four or so species found here. Descriptions are based on unhelpfully variable pelage coloration, hind foot length, ear length, and relative tail length, and patterning of the enamel on molar teeth. The length measures overlap widely among species. Let’s see, is the tail 30 to 44 percent of total length, or is it 30 percent or less of total length? Wuh? What if it’s exactly 30 percent?

And how to measure such things on a live, in situ critter?

Is the fur brownish grey or reddish brown, and is the tail mildly two-tone or not?

Fur glinting in the sunlight.

Well, what struck me first was how small this animal was (based on my experiences with Townsend’s and meadow voles), and how small its eyes and ears were (eyes less than 4 mm in diameter). My first guess is Creeping Vole, Microtus oregoni.

Vole runs. They were extensive, more conspicuous than usual at this site. Perhaps they had been constructed beneath the heavy Christmas snow.

The natural history of the Creeping Vole is not well known. Like other species, it makes surface runs through dense turf. According to Nagorsen (2005:274), “The Creeping Vole evidently makes surface runways in grassy meadows, but they tend to be less conspicuous than those made by the larger Townsend’s Vole. A semi-fossorial rodent, the Creeping Vole constructs shallow tunnels in the soil. Several authorities have reported capturing Creeping Voles in mole tunnels.”

At least I'm certain what this was. Eagle du jour.


Nagorsen, D.W. 2005. Rodents & Lagomorphs of British Columbia. Royal British Columbia Museum.


Karen said...

Hm, hope that vole creeps a little faster, or it will end up as a snack for Mr. Eagle...

Adrian Thysse, FCD. said...

What are sparrows if not winged voles?

kompoStella said...

is that eagle in your backyard? spotting an eagle is thrilling and yet i do think i'd be a wee bit nervous to have it as close as your friend Bret... it looks so intensely serious :-)

PSYL said...

Sweet! I'll have to be on the lookout for this little fellow next time I am there.

Sighting of mammals is much more rarer than birds, hence makes it more exciting for me. But true, small rodent identifications are a pain.

Hugh said...

Karen, the way the vole was acting, I wonder if it hadn't just narrowly escaped (not entirely unscathed) something. The most likely predators would be coyote or heron.

Adrian, Hah, that would fit.

kompoStella, When we first moved into this home, a neighbour had a tall cottonwood tree in which an eagle would perch. It would stare (hungrily?) at our son, who was a toddler at the time. Or was it out of puzzlement(more likely?).

PSYL, Look among the vole runs just north of the golf course fenceline.