A shrew is a small, insectivorous mammal characterized by a long, pointed snout and a high metabolic rate. Often confused with rodents, shrews belong to the order Eulipotyphla, sharing it with hedgehogs and moles. Shrews utilize underground tunnels for shelter and hunting, but their method of acquiring these subterranean spaces differs significantly from that of the mole.
Defining the Shrew’s Habitat Strategy
Shrews employ an opportunistic approach to securing underground shelter, relying on exploiting existing features rather than strenuous excavation. They frequently utilize pre-dug tunnels and runs created by other small mammals, such as voles, mice, or moles. This strategy conserves energy, allowing the shrew to focus on its constant foraging needs.
When shrews create their own burrows, they typically form shallow, surface-level runs or small, simple tunnels. These self-excavated burrows usually only extend a few inches below the surface, averaging around four inches in depth. While their strong front feet enable them to dig through loose soil, they rarely construct the deep, extensive networks associated with true subterranean dwellers. They often kick the loose dirt out behind them or push it away with their snout.
These small, self-made tunnels often serve as access points to existing natural cavities, dense vegetation, or the expansive tunnel systems of other creatures. The shrew’s ability to quickly access and commandeer existing pathways in the soil, leaf litter, or under rocks is a defining feature of its habitat strategy. This flexible behavior allows them to rapidly establish residence and begin hunting.
Distinguishing Shrew Tunnels from Mole Tunnels
The physical evidence left behind provides a clear distinction between shrew and mole tunneling behaviors. Moles are true fossorial specialists, spending almost their entire lives underground creating expansive, permanent tunnel systems. Their signature excavation is the molehill, a symmetrical mound of soil pushed up from deep beneath the surface as they dig new tunnels.
Mole feeding tunnels typically run between six and twelve inches deep, creating noticeable raised ridges or “runways” across the surface. Their large, paddle-like forefeet, rotated outward, are perfectly adapted for efficient digging. These tunnels are built primarily to trap and hunt prey, such as earthworms and grubs, which fall into the open shaft.
Shrews produce little to no significant mounds of dirt because their tunnels are much shallower and less extensive. When a shrew digs an entrance hole to the surface, it is small, typically about one inch in diameter, appearing as a simple, open hole in the ground. These small openings are distinct from the pushed-up ridges and large dirt piles that are the unmistakable signs of a mole’s presence. Shrew runs often follow existing cover, like debris or long grasses, rather than carving deep, symmetrical passages in the open soil.
The Role of Tunnels in Shrew Survival
Tunnels are an indispensable resource for the shrew, directly supporting its demanding physiology. Shrews possess one of the highest metabolic rates among all mammals, requiring them to consume food equal to or exceeding their own body weight daily. Due to this intense energy expenditure, a shrew can only survive for a few hours without eating before succumbing to starvation.
The subterranean pathways serve as efficient, protected hunting grounds, allowing the shrew to access a constant supply of prey, including insects, larvae, and earthworms. Moving through existing tunnels is a more energy-efficient means of foraging than hunting exclusively above ground. Tunnels also offer protection from predators, such as birds of prey, snakes, and domestic cats.
These underground networks provide shelter from severe weather conditions and temperature fluctuations. By retreating into the soil, the shrew can better regulate its body temperature, which is important given its small size and high surface-area-to-volume ratio. This use of tunnels for foraging and shelter is a direct behavioral adaptation to manage their extreme metabolic demands.