Some Ways Mammals Stay Warm In Winter
When temperatures drop significantly, mammals that stay active in the winter have a variety of ways to keep warm, one of which is to have layers of insulation to prevent their body heat from escaping. Often there is a layer of fat under the skin. In addition to providing a source of energy, fat doesn’t transfer heat as well as other tissues such as muscle or skin, and thus helps to insulate an animal’s body. The next layer consists of a short, dense coat of underfur which is filled with air pockets that provide insulation. Lastly there frequently is a third layer of oily, water-repellent guard hairs which excel at keeping out water. They are often transparent and hollow, providing extra thermal insulation.
Voles, mice, shrews and red squirrels use elaborate tunnels systems under the snow to escape cold temperatures and strong winds. Flying Squirrels huddle together in groups to keep warm. Shivering is a warming technique used by many mammals, including humans. And some active animals, like the pictured Gray Squirrel, simply find a sheltered spot in the sun, close their eyes, and soak up the warmth! (Thanks to Jody Crosby for photo op.)
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American Crow Bills Used As Tools
American crows obtain most of their food on the ground as they walk along in search of seeds, insects, frogs, snakes, bird nests and small mammals. Their hunting techniques are varied and most involve the use of their bill. In search of invertebrates, crows will probe the soil with their bill, flick aside leaves, dig in the soil and even lift cow paddies. They fish for tadpoles and dig nearly an inch deep with their bill for clams. In winter, their foraging continues and as these tracks indicate, when the snow is only a few inches deep they will walk around and around in a given area, probing tufts of grass for hibernating insects, mice, voles, or any other form of life these opportunists find.
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Meadow Vole Tunnels Exposed
If you live where the snow is actually melting, a labyrinth of vole tunnels may be revealing itself to you. These tunnels were excavated in the snow next to the ground in what is referred to as the subnivean layer. They lead from sleeping areas to known sources of food, and are advantageous to both mice and voles that travel in them – they provide thermal insulation by protecting them from the wind and cold, and they keep these rodents hidden from predators. Carbon dioxide, which builds up in the subnivean layer from animal respiration as well as CO₂ released from the ground, escapes through ventilation shafts, or air vents, that lead up to the surface of the snow.
Voles stay in these tunnels as long as the snow is deep enough not to expose them, finding food in the form of plants, seeds and bark from bushes and shrubs as they dig through the snow. This winter has provided voles, mice and shrews with an extended period of protection, as hungry barred owls attest to.
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Coyotes Feeding on Deer Carcasses
Ninety percent of a coyote’s diet is animal matter, including creatures as varied as meadow voles, mice, muskrats, raccoons, beetles and grasshoppers — basically, anything it can outrun. Coyotes have the reputation as major predators of deer. While research confirms that deer (and rabbits) comprise a good portion of a coyote’s diet in the Northeast, the majority of the deer that coyotes consume is scavenged as carrion (see photo). Because they cannot move as fast as adult deer, fawns are more vulnerable to coyote predation.
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Barred Owl Story in the Snow
These beautiful impressions in the snow tell the story of a Barred Owl diving feet first after prey, most likely a vole or mouse. The fact that there are no rodent tracks on the surface of the snow tells you that the mouse or vole was well hidden in its tunnel under the snow at the time. Apparently the owl’s talons did not reach their target (at least, no blood or rodent remnants), and the owl continued to plow through the snow in repeated attempts to capture its prey before taking flight.
The presence of facial discs (feathers in the shape of a funnel around each eye that direct sound waves towards the owl’s ear) plus the differing size and asymmetrical placement of an owl’s ear openings allow the owl to discern the direction a sound is coming from, how far away it is and its height relative to the owl – even in the dark or under the snow! The exceptional hearing ability of owls, particularly those in the genus Strix (which includes Barred and Great Gray Owls), enables them to plunge into the snow and often successfully capture prey, sight unseen. (Species of owl was determined by wing length. Thanks to Rob Anderegg and Jennifer Grant for photo op.)
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Hide & Seek: Voles & Foxes
Unlike wolves, which hunt in packs and often take down prey larger than themselves, red foxes are solitary hunters and as a result often catch prey much smaller than themselves, such as mice and voles. During the winter, mice and voles become more active during daylight hours because much of their time is spent under the snow, where they remain hidden from view. Consequently, in winter you’re more likely to see a fox hunting during the day than in the summer. Whenever it’s hunting, night or day, a fox depends heavily on its acute sense of hearing. It is most sensitive to lower noises such as the rustling and gnawing sounds that small animals make as they move through vegetation or feed on seeds, buds and twigs. Foxes can locate these sounds several feet away, to within inches of their true location, under three feet of snow. Recent research suggests that they may also use the magnetic field to help them locate prey. (photo: red fox & meadow vole tracks)
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Distinguishing Vole from Mouse Tracks
Meadow Voles (Microtus pennsylvanicus) and White-footed Mice (Peromyscus leucopus) are two of our most common species of small rodents, and they both remain active in winter. Their feet are roughly the same size (approximately ¼ ” wide by ½” long), but the tracks they leave differ slightly, due to their differing gaits. White-footed Mice bound, leaving tracks that have a four-print pattern (parallel larger hind feet in front of smaller, parallel front feet) often with a long tail drag mark in between each set of tracks. Meadow Voles have a variety of gaits, the most common being a trot, which leaves an alternate-track trail, with the hind feet directly registering in the tracks of the front feet. Although voles can also leave a tail mark, they do so much less often than mice. Once the depth of the snow is significant, mouse tracks are more common, as voles tend to travel primarily through tunnels they’ve created under the snow.
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Mice vs. Voles
Mice and voles are commonly lumped together, probably because the differences between them are so slight. Both are small, furry rodents, but mice generally have large eyes, large ears and long tails (close to or greater than the length of their bodies). Voles have smaller eyes, smaller ears (often concealed in their fur), and shorter tails. Voles tend to be active day and night, whereas mice are mainly nocturnal. ( Meadow voles are commonly referred to as “field mice,” which tends to add to the confusion regarding these two groups of mammals!) There are five species of mice in New England (white-footed, deer, house, meadow jumping and woodland jumping), and four species of voles (meadow, southern red-backed, rock and woodland).
Meadow Vole Trail
Thanks to a dusting of snow we are suddenly privy to the comings and goings of the creatures we live amongst. Some animals are small enough to remain hidden once winter snows arrive, because they live in the subnivean layer between the surface of the ground and the snow. But when the snow is too shallow for them to create this network of tunnels, their movements are easily discernible. The pictured meadow vole trail shows where the vole initially tried (unsuccessfully) to tunnel under the snow (it wasn’t deep enough), at the bottom of the photograph. It then scampered over the grass until it stopped to rest for a moment, leaving a whole body imprint, including its short tail. It’s fairly unusual to see the entire body print of small rodents such as voles and mice, for they are so vulnerable out in the open that they rarely stop long enough to leave one.
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