A burrow is a tunnel or hole that an animal digs for habitation (a place to live) or as a temporary refuge (a place of protection). Burrows can also be the byproduct of locomotion—moving from one place to another. Some burrows function as “larders,” where animals keep food.
Burrows provide shelter from predators and extreme temperatures. For these reasons, animals have used burrowing behavior for a very long time. In fact, a 110-million-year-old dinosaur burrow was recently discovered on the southeastern coast of what is now Australia. It is the oldest known dinosaur burrow, and is nearly identical to the first one ever found, in the U.S. state of Montana in 2006. This similarity suggests burrows were dug by similar dinosaur species on opposite ends of the Earth for millions of years.
Sometimes, entire families live in burrows. Beavers, for instance, construct complex lodges (sometimes called dams) that provide shelter for parents and offspring. Other times, burrows are dug primarily for pregnant mothers and infant offspring. Maternity dens used by bears are probably the most familiar example of this type of burrow.
Besides protection from predators and climate, some burrows function as food-storage facilities. Kangaroo rats are very small rodents—only weighing about 150 grams (5 ounces)—but they store grain in huge burrows many times their size. These “granaries” can store up to 120 liters (32 gallons) of food.
Burrowing is popular among many types of animals, including invertebrates, which are animals lacking a spinal column. Clams, crustaceans, insects, sea urchins, spiders, and worms all exhibit burrowing behavior. Various amphibians, including some species of frogs, are burrowers, as are a number of reptiles, including assorted snakes. Even some birds are burrowers. Kingfishers, Magellanic penguins, and puffins are among those known to make burrows instead of nests.
However, the most well-known burrowers are probably mammals, especially the mole, gopher, groundhog (also known as a woodchuck), and rabbit. Bears are most likely the largest burrowing animals. They use shelters such as caves, as well as dug-out earthen and snow burrows, as their dens. Most species spend the winter inside these dens in a long period of sleep similar to hibernation.
Animals construct burrows in many types of surfaces. Scabies mites dig into the skin of animals and humans. Termites chew through wood, including fallen or even living trees. Birds typically burrow in soft soil. Kangaroo mice use fine sand. Some clams and sea urchins can burrow into rock. Moles often burrow into lawns and raise molehills. The nine-banded armadillo builds its burrow in moist soil near creeks or streams. Pregnant female polar bears create maternity dens in earth or snow to give birth and nurture their cubs.
Burrows range in complexity from simple, short tubes to elaborate networks of connected chambers and tunnels.
Groundhogs are exceptional burrowers and their burrows are particularly large. It is estimated that an average groundhog moves 1 cubic meter (35 cubic feet) of soil when digging a burrow, which may have up to 14 meters (46 feet) of tunnels buried up to 1.5 meters (5 feet) underground. A well-developed rabbit warren—a group of burrows—may be thousands of meters long.
Beavers create an unusual type of burrow. Beaver lodges are constructed with tree branches and mud over banks or hills in creeks or ponds. Every year in late autumn, beavers cover their lodges with fresh mud. Only after the lodge is built do beavers dig burrows beneath them. All their burrows have underwater entrances, making it difficult for other animals to invade. When the frost comes, the mud on top of the lodge freezes, becoming almost as hard as stone and unable to be penetrated by predators, such as wolves and wolverines. Most beaver lodges have two rooms. The first is used for drying off after a beaver swims up to the burrow. The second, warmer and drier, is where the beaver family lives.
Some animals prefer not to dig their own burrows, but to use ones made by other animals instead. The meerkat is one example. A colony of meerkats, which averages 20 to 30 members and is called a “mob” or “gang,” often uses burrows dug by ground squirrels or mongooses. Meerkats do not compete with those species for resources, and sometimes even share the space with them. Meerkats have also been known to share burrows with snakes, although they most likely do not do so on purpose.
A meerkat burrow can have as many as 90 entrances and be 2 meters (6.5 feet) deep. The meerkats only leave them during the day, and when they do, one or more will stand guard while the rest of the gang is foraging or playing. As soon as a guard spots a predator, it will give a warning bark and the other gang members will run and hide in the many holes of the burrow.
Burrows and the Environment
Animal burrows can pose threats to the environment, as well as to human agricultural and residential development.
Gophers dig tunnels in the ground and place mounds of dirt and rocks at their entrances. These are often referred to as “gopher towns” or “gopher holes.” A gopher town can have a population in the thousands and take over large sections of mountain meadow or prairie, destroying plant life and leaving large stretches of bare dirt. This land is more vulnerable to erosion and flooding. Gopher towns can also disrupt garden plots, landscaping, and even some underground cables.
Groundhog burrows can damage farm machinery. Wheels or other implements, for instance, may abruptly fall into a large, burrowed area, delaying work and damaging the machinery’s structure. Groundhog burrows can even undermine the foundations of buildings.
Termites can do extensive damage to wooden structures and unprotected buildings. Once they have entered a building, they may destroy carpet, cloth, paper, and other materials containing cellulose, an organic compound found in plants that is the primary diet of termites. In the southwestern United States alone, termites cause approximately $1.5 billion in structural damage each year. They can also be major agricultural pests, especially in Africa and Asia, where crop damage can be extensive.
Prairie-dog towns, one of the most familiar types of burrow networks, are often found on land where livestock graze. Black-tailed prairie dogs, native to the Great Plains of North America, create enormous networks of burrows, some stretching more than 64,000 square kilometers (25,000 square miles) and containing about 400,000 prairie dogs. Prairie dogs prefer to dig their burrows in short grasses, making livestock pastures an ideal location for towns. This puts livestock, such as cattle and sheep, at risk for injury. Some predators attracted to prairie-dog towns, such as coyotes and bobcats, may also threaten livestock.
However, the prairie-dog diet (mostly grasses) encourages the growth of forbs, such as sunflowers and clover. The abundance of forbs attracts animals such as bison—and provides more nutrient-rich fodder for livestock.
In the 20th century, ranchers used poisons and hunting techniques to eradicate prairie-dog towns. The primary predator of the black-tailed prairie dog, the black-footed ferret, was almost driven to extinction.
Injuries to livestock caused by prairie-dog towns still cost ranchers hundreds of thousands of dollars a year.
The few prairie-dog towns that exist today are mostly in conservation areas and national parks.
Burrows are one of the most common types of trace fossils, the preserved evidence of the presence or behavior of an ancient organism. Trace fossils of clam burrows, preserved in rock, may help prove that a desert was once underwater.
Fierce-looking warthogs are more often prey than predator on the African savanna. Warthog mothers use large networks of burrows to protect their piglets from lions, hyenas, leopards, and cheetahs. Most predators stay away from the narrow burrows, for fear of a warthog mother's sharp tusks.
Scientists and engineers are currently experimenting with RoboClam, a robot that mimics the extraordinary digging ability of the razor clam. RoboClam could be used for smart anchors (high-tech anchors that burrow through the ocean floor instead of sitting on top of it), tethers for robotic submarines, or detonators for underwater mines.
a slope of land adjoining a body of water, or a large elevated area of the sea floor.
dome-shaped den built by beavers over a burrow in a stream or pond.
small hole or tunnel used for shelter.
complex carbohydrate that forms the tough, rigid cell wall of most plants and is necessary for such products as paper and textiles.
all weather conditions for a given location over a period of time.
management of a natural resource to prevent exploitation, destruction, or neglect.
construction or preparation of land for housing, industry, or agriculture.
foods eaten by a specific group of people or other organisms.
conditions that surround and influence an organism or community.
to destroy or remove.
act in which earth is worn away, often by water, wind, or ice.
process of complete disappearance of a species from Earth.
broad-leafed herb (not grass), especially one growing in a meadow or prairie.
structure on which a building is constructed.
harvested seed of such grasses as wheat, oats, and rice.
grassland region of North America, between the Rocky Mountains and the Mississippi River.
dwelling or place where an organism lives (habitates).
state of reduced physiological activity, similar to sleep, in which some animals spend the winter.
animal without a spine.
room or place where food is kept.
animals raised for human use.
animal with hair that gives birth to live offspring. Female mammals produce milk to feed their offspring.
sheltered place where a mother animal gives birth and nurtures her young.
wide area of grassland.
geographic area protected by the national government of a country.
to support, care for, and protect.
substance an organism needs for energy, growth, and life.
large grassland; usually associated with the Mississippi River Valley in the United States.
large network of prairie-dog burrows, stretched thousands of acres and containing hundreds of prairie-dog families.
animal that hunts other animals for food.
person who owns or manages a livestock farm (ranch).
shelter or protection from danger.
order of mammals often characterized by long teeth for gnawing and nibbling.
base of hard material on which a non-moving organism grows. Also called substratum.
degree of hotness or coldness measured by a thermometer with a numerical scale.
burrow or series of connected burrows used by rabbits.