An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, and can be found in nearly every biome and among various biological interactions. Many animal species are known to form burrows. These species range from small invertebrates, such as the ''

Corophium arenarium ''Corophium arenarium'' is a small (up to ) European amphipod crustacean of the family Corophiidae. It looks very similar to '' C. volutator''. It burrows in bottom sediments, between deep. ''Corophium arenarium'' originates from the coasts of ...

'', to very large vertebrate species such as the

polar bear The polar bear (''Ursus maritimus'') is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear specie ...

. Burrows can be constructed into a wide variety of substrates and can range in complexity from a simple tube a few centimeters long to a complex network of interconnecting tunnels and chambers hundreds or thousands of meters in total length; an example of the latter level of complexity, a well-developed burrow, would be a

rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit speci ...

warren A warren is a network of wild rodent or lagomorph, typically rabbit burrows. Domestic warrens are artificial, enclosed establishment of animal husbandry dedicated to the raising of rabbits for meat and fur. The term evolved from the medieval Angl ...

Vertebrate burrows

A large variety of vertebrates construct or use burrows in many types of substrate; burrows can range widely in complexity. Some examples of vertebrate burrowing animals include a number of mammals,

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

s, fish ( dragonet and lungfish),

reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...

, and

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

(including small dinosaurs). Mammals are perhaps most well known for burrowing. Mammal species such as Insectivora like the mole, and rodents like the gopher, great gerbil and groundhog are often found to form burrows. Some other mammals that are known to burrow are the platypus,

pangolin Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (, from Ancient Greek ϕολιδωτός – "clad in scales"). The one extant family, the Manidae, has three genera: '' Manis'', '' Phataginus'', and '' Smut ...

pygmy rabbit The pygmy rabbit (''Brachylagus idahoensis'') is a rabbit species native to the United States. It is also the only native rabbit species in North America to dig its own burrow. The pygmy rabbit differs significantly from species within either the ...

armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, along wi ...

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...

and weasel. The

, a member of the family Lagomorpha, is a well-known burrower. Some species such as the groundhog can construct burrows that occupy a full cubic metre, displacing about of dirt. There is evidence that rodents may construct the most complex burrows of all vertebrate burrowing species. For example, great gerbils live in family groups in extensive burrows, which can be seen on satellite images. Even the unoccupied burrows can remain visible in the landscape for years. The burrows are distributed regularly, although the occupied burrows appear to be clustered in space. Even

Carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

like the

meerkat MeerKAT, originally the Karoo Array Telescope, is a radio telescope consisting of 64 antennas in the Meerkat National Park, in the Northern Cape of South Africa. In 2003, South Africa submitted an expression of interest to host the Square Kilom ...

, and

marsupials Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

, such as wombats are burrowers. The largest burrowing animal is probably the

when it makes its maternity den in snow or earth.

Lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...

are also known to construct and live in burrows, and may exhibit territorial behaviour over the burrows as well. There is also evidence that a burrow provides protection for the Adelaide pygmy blue-tongue skink (''Tiliqua adelaidensis'') when fighting, as they may fight from inside their burrows. Burrows by birds are usually made in soft soils; some penguins and other pelagic seabirds are noted for such burrows. The Magellanic penguin is an example, constructing burrows along coastal

Patagonian Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

regions of Chile and Argentina.C. Michael Hogan, (2008
''Magellanic penguin'', Globaltwitcher.com, ed. Nicklas Stromberg
/ref> Other burrowing birds are

puffin Puffins are any of three species of small alcids (auks) in the bird genus ''Fratercula''. These are pelagic seabirds that feed primarily by diving in the water. They breed in large colonies on coastal cliffs or offshore islands, nesting in crev ...

s, kingfishers, and

bee-eaters The bee-eaters are a group of non-passerine birds in the family Meropidae, containing three genera and thirty species. Most species are found in Africa and Asia, with a few in southern Europe, Australia, and New Guinea. They are characterised by ...

Kangaroo mice A kangaroo mouse is either one of the two species of jumping mouse (genus ''Microdipodops'') native to the deserts of the southwestern United States, predominantly found in the state of Nevada. The name "kangaroo mouse" refers to the species' ex ...

construct burrows in fine sand.

Invertebrate burrows

Scabies Scabies (; also sometimes known as the seven-year itch) is a contagious skin infestation by the mite ''Sarcoptes scabiei''. The most common symptoms are severe itchiness and a pimple-like rash. Occasionally, tiny burrows may appear on the skin ...

mites Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

construct their burrows in the skin of the infested animal or human. Termites and some wasps construct burrows in the soil and wood. Ants construct burrows in the soil. Some

sea urchins Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

and clams can burrow into rock. The burrows produced by invertebrate animals can be filled actively or passively. Dwelling burrows which remain open during the occupation by an organism are filled passively, by gravity rather than by the organism. Actively filled burrows, on the other hand, are filled with material by the burrowing organism itself. The establishment of an invertebrate burrow often involves the soaking of surrounding sediment in mucus to prevent collapse and to seal off water flow. Examples of burrowing invertebrates are insects,

spiders Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species dive ...

, crustaceans, clams and worms.

Excavators, modifiers, and occupants

Burrowing animals can be divided into three categories: primary excavators, secondary modifiers and simple occupants. Primary excavators are the animals that originally dig and construct the burrow, and are generally very strong. Some animals considered to be primary excavators are the

prairie dog Prairie dogs (genus ''Cynomys'') are herbivorous burrowing ground squirrels native to the grasslands of North America. Within the genus are five species: black-tailed, white-tailed, Gunnison's, Utah, and Mexican prairie dogs. In Mexico, p ...

and the aardvark.

Pygmy gerbil The pygmy gerbil (''Gerbillus henleyi'') is distributed mainly in Algeria to Israel and the Arabian Peninsula. It is also known as Henley's gerbil or pygmy dipodil. ''Gerbillus henleyi'' is a long-tailed small gerbil with a back coat that is dar ...

s are an example of secondary modifiers, as they do not build an original burrow, but will live inside a burrow made by other animals and improve or change some aspects of the burrow for their own purpose. The third category, simple occupants, neither build nor modify the burrow but simply live inside or use it for their own purpose. Some species of bird make use of burrows built by tortoises, which is an example of simple occupancy. These animals can also be referred to as commensals.

Protection

Some species may spend the majority of their days inside a burrow, indicating it must have good conditions and provide some benefit to the animal. Burrows may be used by certain species as protection from harsh conditions, or from predators. Burrows may be found facing the direction of sunlight or away from the direction of cold wind. This could help with heat retention and insulation, providing protection from temperatures and conditions outside. Insects such as the earwig may construct burrows to live in during winter, and use them for physical protection. Some species will also use burrows to store and protect food. This provides a benefit to the animal as it can keep food away from other competition. It also allows the animal to keep a good stock of food inside the burrow to avoid extreme weather conditions or seasons where certain food sources may be unavailable. Additionally, burrows can provide protection to animals that have just had their young, providing good conditions and safety for vulnerable newborn animals. Burrows may also provide shelter to animals residing in areas frequently destroyed by fire, as animals deep underground in a burrow may be kept dry, safe and at a stable temperature.

Fossil burrows

Burrows are also commonly preserved in the fossil record as

burrow fossil Burrow fossils are the remains of burrows - holes or tunnels excavated into the ground or seafloor - by animals to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion preserved in the rock record. Because bu ...

s, a type of trace fossil.

References