Voles are small, short-tailed rodents often confused with mice or moles due to their size and subterranean activity. These creatures, mainly belonging to the genus Microtus, are characterized by their robust bodies and relatively short limbs. Voles are highly active throughout the entire winter season, relying on adaptations that allow them to thrive even under a blanket of snow.
Vole Activity During Cold Weather
Voles are classified as non-hibernating mammals, meaning they do not enter a state of torpor to conserve energy when temperatures drop. Their high metabolic rate requires continuous activity and constant foraging to fuel their internal temperature regulation. They cannot rely on stored body fat alone when external food resources are scarce.
Voles maintain typical cycles of rest and activity throughout the winter, often alternating between periods of sleep and intense foraging every few hours. This continuous movement and feeding sustains their core body temperature against the cold. Some species even continue to breed during the winter months. Their behavior is dictated by the need to remain hidden from predators and avoid the harshest surface weather.
The Subnivean Zone: A Hidden World
Vole activity is made possible by the subnivean zone, a specialized microhabitat that forms beneath a deep, insulating layer of snow. This protective space is located directly between the ground surface and the snowpack, essentially creating an underground world. The structure of the snow traps the heat radiating from the soil below, preventing it from escaping into the cold air.
Snow acts as an effective insulator. Even when air temperatures drop significantly below freezing, the subnivean zone remains near the freezing point, typically hovering around 0°C (32°F). This thermal stability provides a mild environment where voles can regulate their body temperature without expending excessive energy, reducing their caloric needs compared to surface travel.
Inside this hidden layer, voles construct intricate tunnel systems that function as protected highways for foraging. These tunnels are created by pushing through loose snow near the ground or by excavating into the topsoil if necessary. The subnivean zone becomes a network of movement and nesting chambers, allowing access to food sources throughout the season. This insulated environment also offers protection from many ground-level predators who cannot easily detect or access the rodents beneath the thick snow cover.
Sustaining Energy: Winter Feeding Habits
The constant energy demand of non-hibernating voles requires a significant shift in winter foraging strategy as above-ground vegetation dies off. Voles adapt by relying on food sources accessible from within their subnivean tunnels or by burrowing beneath the soil. Their diet shifts to include roots, tubers, and previously stored food like seeds or plant bulbs.
The need for continuous calories drives the consumption of bark from trees and shrubs, known as girdling. Voles gnaw away the outer layer of bark and the underlying cambium layer, typically near the base of young woody plants accessible from their snow tunnels. This activity secures necessary nutrients and fiber when other food is unavailable. However, it can severely damage or kill the plant by interrupting nutrient flow.
The persistent need to find and consume food continuously is the primary driver of their winter activity, directly linked to maintaining their small body mass and high internal temperature. Because of their high metabolism, voles need to feed every few hours throughout the day and night to avoid starvation, which necessitates constant movement through their tunnel systems.
Practical Signs of Winter Vole Presence
While voles spend the winter out of sight beneath the snow, their activity leaves clear evidence visible once the snow melts. One common sign is the presence of narrow, meandering “runways” or paths pressed down into the grass or soil surface. These pathways show where voles traveled extensively under the snow, compacting the vegetation below.
Homeowners often notice smooth, clean-edged girdling damage on the base of small trees, saplings, or shrubs, confirming winter feeding. This damage is usually low to the ground and distinct from the ragged tears left by larger animals. Small, scattered burrow openings, typically about an inch or two in diameter, also become noticeable in the spring as the snow recedes, confirming the extent of their winter tunneling network.