Tiny Tunnels

As I shoveled my way to the bird feeder recently, I uncovered small tunnels (roughly the diameter of a quarter) leading directly to the seeds scattered at the base of our feeder. I suspected perhaps it was shrew, moles and voles, but honestly knew nothing about any of them.

Now curious about this extensive network of tunnels beneath the snow, I headed straight for the Internet. My initial Google search revealed a “Northern Mole Vole”, but it lives on a different continent (Northern Afghanistan, Ukraine, Mongolia, China) and is not my culprit. The highlights of my investigation follow:

The name of the region where snow cover meets soil is the subnivean zone. Insulated by a thick, snowy, thermal blanket, a variety of creatures take advantage of the snowy cover from predators to tunnel and breed freely during the winter. When the snow begins to melt this spring, watch for their mini mazes of inter-connecting trails, runways, tunnels and occasional nest of grasses.

Adult Moles moles measure 5 to 8 inches long which is too large for these little tunnels. In addition to living and tunneling in the soil below the frost line, far below the snow, they prefer to eat insects and worms, not plant matter or seeds. Moles tunnel quickly. Unlike voles, they surface occasionally. When they surface it creates a mini-volcano-like dirt mound. Moles are not the creatures whose tunnels I uncovered.

Although the Northern Short-tailed Shrew prefers to tunnel in the subnivean zone, shrews are also too large. They measure almost 5” long, and also prefer insects over seeds and plants. A note of caution for you, shrews are venomous mammals with toxic saliva. Anyone who tries to handle a shrew, may receive a painful bite caused by their venom which can paralyze or kill small animals.

Pine Voles measure just 3-4 inches from their nose to their bottom (not including their short tail), and dig tunnels less than 2” in diameter. Their dining habits can be particularly upsetting to gardeners and homeowners since they really enjoy dining on plants. Pine Voles don't make my list of suspects either since their nests and tunnels are about a foot below ground in light, loamy soil.

Meadow Voles are the most likely candidate. They spend most of their time above the ground or in shallow tunnels in dirt or snow. Measuring 3.5 to 5 inches long from nose to bottom, they have tails about 2 inches long. Meadow Voles' eat plant matter, seeds and some insect parts. They seem to be a perfect match.

These are all fascinating creatures. Most of them eat more than their own weight each day. They can tunnel quickly. Voles breed prolifically throughout the year, bearing as many as 40 young per breeding female annually. Which is great for their predators, since they are an important food source for hawks, owls, coyotes, snakes and foxes. Due to their popularity among predators, their life expectancy is rarely more than a year.

With the deep snow cover we've had this winter, predators like owls, hawks, etc. will have trouble finding prey which will affect their populations. Meanwhile, under this deep cover, the populations of moles, voles and shrew will grow rapidly since they each have multiple litters each year with broods ranging from 3 to 10 young.

With this information, I might be tempted to trap them or use deterrents. But, as difficult as all this snow has been for me to deal with, my sympathies go out to all creatures trying to survive in this environment. So, they're safe for now. I'll just be sure to keep the feeders full so there is enough for the birds to share with these subnivean creatures.

I encourage you to visit my sources for more amazing facts:

Down to Earth, Specialists in Education, Leadership and Training. http://www.down2earth.org/funstuff8.htm

URI Mole Fact Sheet: http://www.urimga.org/fact_sheets/Moles.pdf

URI Vole Fact Sheet: http://www.uri.edu/ce/factsheets/sheets/voles.html

WikiPedia: http://en.wikipedia.org/wiki/Northern_Short-tailed_Shrew

The great illustration above is by Mary Lamb-Greene. I found it at KidoInfo's blog from a review of “Living Under the Snow”, a children's book written by local author Kristen Swanberg, who is the Senior Director of Conservation, Audubon Society of Rhode Island.