You may still be grumbling about last week’s snowstorm, but the snow offers new ways of “seeing” what wildlife shares our space. Even if we don’t actually see the animals, the indirect evidence of their presence is there to see. In our last issue, we discussed reading the “stories in the snow” left by footprints and wing prints on the surface of the snow. However, there are “undercover operatives” spending the winter beneath the snow in what is called the subnivean zone. This is the area between the bottom of the snowpack and the surface of the ground beneath. The word subnivean comes from the Latin “sub” (under) and “nives” (snow).
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For example, you may see what look like trails made by snakes under the snow…but reptiles are cold blooded and retreat to hibernacula (temperature controlled hideaways) to escape frigid weather. So what is creating these tunnels under the snow?
Look closely; these trails are made by the foot traffic of small animals as they travel back and forth under the snow. Follow the trails a little further, and you will likely see that the tracks disappear into a small hole in the snow. You have just found an entrance into a network of tunnels where mice, meadow voles, and shrews make their cozy winter homes.
(Photos by Rod Planck)
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When snow accumulates across our Michigan landscapes, we often assume that little animals are sleeping away the cold winter days and nights, awaiting the spring thaw. Actually, the snow’s insulation quality creates a sheltered environment for some small animals, allowing them to stay relatively active during the winter months. Mice, voles, and shrews retreat here for protection from cold temperatures, bitter winds, and hungry predators. Under the snow, these tiny mammals create long tunnel systems complete with air shafts to the surface above.
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It takes only six inches of snow for mice, voles, and shrews to have a sturdy roof over their heads and roomy living quarters below. Add another two inches and the subnivean zone remains within a degree or two of 32°F, regardless of the temperature and weather conditions in the outside world. Deluxe subnivean accommodations feature a sleeping area, a breakfast nook, a food cache corner, and a latrine. (Illustration by Adelaide Tyrol)
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Photo below by Grace Bartlett
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Food is right at hand for mice and voles. Seeds, as well as leaves and stems of grasses are collected, and occasionally roots and bulbs. Voles often take up residence under bird feeders where the seed is scattered and litters the ground. They will sometimes cache, or store up, small amounts of food, to ensure a steady supply. While these animals are active throughout the winter, they do spend small amounts of time huddled together in a deep sleep, waking occasionally to feed. [To learn how shrews adapt to winter, read “Did You Know?” below]
These subnivean tunnels are revealed as layers of snow melt away. It’s likely that we’ll be shoveling more snow before the spring ephemerals bloom, so you have more time to practice your “undercover investigations.”
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Smithsonian Magazine reports, “Shrews are all around weird. Found around the world, they are one of nature's few venomous mammals. And they are ferocious, dubbed the 'the tigers of the small animal world.' Shrews typically catch and consume mainly of invertebrates, such as earthworms, millipedes, spiders, and insects, however, plant material and small vertebrates [like mice and voles!] are eaten as well." Now another "weird" adaptation is the focus of research. (Photo Christian Ziegler)
Common shrews shrink their heads — including their skulls — in winter, researchers have found. They believe that this dramatic example of downsizing may help the animals to survive when food is scarce.
Individual wild common shrews (Sorex araneus) captured and tagged in Germany showed large reductions in skull size and body mass over the winter. Their spines also got shorter, and major organs, including the heart, lungs and spleen, shrank.
"Even their brain mass dropped by 20–30%, according to Javier Lázaro, a biologist at the Max Planck Institute for Ornithology in Radolfzell, Germany. In spring, the animals started to regrow. 'We hypothesize that these seasonal changes could have adaptive value,' says Lázaro, who led the work."
Common shrews have one of the highest metabolic rates among mammals and they neither hibernate nor store food. This means shrews must consume as much as three times their weight in food per day, eating every 2-3 hours. Because they burn fat reserves quickly, they often starve to death after only a few hours without food.
Reducing their body mass during winter might increase their chances of survival, because they wouldn’t need so much food. In particular, he adds, “reducing brain size might save energy, as the brain is energetically so expensive”.
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You Know Winter Has Arrived When the Redpolls Are Here! |
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The Environmental Study Area (ESA) recently hosted an especially energetic and feisty flock of winter wanderers. A group of several dozen Common Redpolls (Acanthis flammea) were seen by Mike O’Leary, who regularly birds the area. Mike was able to enjoy observing the redpolls as they extracted tiny seeds from the cones of alder trees along the bank of the Rouge River, not far from the Henry Ford Estate. (Photo by Jim Simek)
Mike’s encounter with the redpolls marks the end of a stretch of recent winters when this species was pretty much absent from the ESA. That’s to be expected, since redpolls only come this far south when their food supplies dwindle in their far northern habitats of open coniferous forest and tundra. These occasional “irruptions” of redpolls and other boreal finches enables us to enjoy their presence in the local winter landscape.
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Common Redpolls can be identified by their small size (smaller than a sparrow), red forehead, and black feathering around the base of the bill. Males have a wash of rosy feathering on their throat and breast. Their behavior is rambunctious.
(Photo Cornell Lab of Ornithology)
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And lest you think that the subnivean zone is just for mammals, common redpolls break through the snow with their heads, then burrow horizontally for up to a foot and a half. Come morning, when the sunshine warms the air, they pop up out of the roosting cave, leaving the smooth blanket of snow pocked with redpoll-sized craters.
The redpolls are likely to stick around our area for at least the next couple of weeks. Look for their tightly-knit flocks moving like a swarm of bees over the landscape, and listen for their burry chatters. Good luck! -Rick Simek
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In this unusual time, venturing outdoors and encountering nature is even more important. Our trails are accessible, so please visit our Environmental Study Area. Check out our Remote Learning Activities & Resources page for ideas to create a “Neighborhood Nature Journal” and “Family Nature Walk” activities! |
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Please stay safe, stay tuned, and stay engaged in learning activities while we eagerly wait for the opportunities to share experiences together. In the meantime, watch for our new online activities to satisfy your curiosity about the natural world. |
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Please remember...
The EIC Environmental Study Area is open daily from sunrise to sunset. We would like to remind nature-goers that fishing on site is prohibited and to leave bikes and dogs at home because they cause disruption and stress to the EIC wildlife.
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