An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against

predation Predation is a biological interaction In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or o ...

and exposure to the elements, and can be found in nearly every

biome A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...

and among various

biological interaction In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species (intraspecific interactions), or of different species ( interspecific interactio ...

s. Many animal species are known to form burrows. These species range from small

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

, such as the '' Corophium arenarium'', to very large

vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...

species such as the polar bear. 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 s ...

warren.

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 Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

, amphibians,

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...

( dragonet and

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

reptiles Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephali ...

, 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 lightweig ...

(including small

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s).

Mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

are perhaps most well known for burrowing. Mammal species such as

Insectivora The order Insectivora (from Latin ''insectum'' "insect" and ''vorare'' "to eat") is a now-abandoned biological grouping within the class of mammals. Some species have now been moved out, leaving the remaining ones in the order Eulipotyphla, ...

like the mole, and

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are roden ...

s like the

gopher Pocket gophers, commonly referred to simply as gophers, are burrowing rodents of the family Geomyidae. The roughly 41 speciesSearch results for "Geomyidae" on thASM Mammal Diversity Database are all endemic to North and Central America. They ar ...

, great gerbil and

groundhog The groundhog (''Marmota monax''), also known as a woodchuck, is a rodent of the family Sciuridae, belonging to the group of large ground squirrels known as marmots. The groundhog is a lowland creature of North America; it is found through mu ...

are often found to form burrows. Some other mammals that are known to burrow are the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monot ...

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 '' Smuts ...

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 th ...

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, al ...

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 Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets and European mink. Members of this genus are small, active predators, with long and slender ...

. The

, a member of the family

Lagomorpha The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae ( pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ ...

, 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 monophyletic order of placental mammals consisting of the most recent common ancestor of all cat-like and dog-like animals, and all descendants of that ancestor. Members of this group are formally referred to as carnivorans, ...

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 K ...

, 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 ...

, such as

wombats Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about in length with small, stubby tails and weigh between . All three of the extant species are members of the family Vombatidae. They are ada ...

are burrowers. The largest burrowing animal is probably the polar bear when it makes its

maternity den A maternity den, in the animal kingdom, is a lair where the mother gives birth and nurtures the young, when they are in a vulnerable life stage. While such dens are typically subterranean, they may also be snow caves or simply beneath rock ledge ...

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 a ...

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 Penguins (order Sphenisciformes , family Spheniscidae ) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: only one species, the Galápagos penguin, is found north of the Equator. Highly adap ...

and other

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

seabirds Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environ ...

are noted for such burrows. The

Magellanic penguin The Magellanic penguin (''Spheniscus magellanicus'') is a South American penguin, breeding in coastal Patagonia, including Argentina, Chile, and the Falkland Islands, with some migrating to Brazil and Uruguay, where they are occasionally see ...

is an example, constructing burrows along coastal Patagonian regions of

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

.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 c ...

kingfisher Kingfishers are a family, the Alcedinidae, of small to medium-sized, brightly colored birds in the order Coraciiformes. They have a cosmopolitan distribution, with most species found in the tropical regions of Africa, Asia, and Oceania ...

s, 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 b ...

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' ...

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 s ...

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 evi ...

construct their burrows in the skin of the infested animal or human.

Termite Termites are small insects that live in colonies and have distinct castes ( eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blat ...

s and some

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...

s 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 Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two sh ...

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

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s are

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

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 di ...

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gr ...

and

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete worm ...

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 ...

and the

aardvark The aardvark ( ; ''Orycteropus afer'') is a medium-sized, burrowing, nocturnal mammal native to Africa. It is the only living species of the order Tubulidentata, although other prehistoric species and genera of Tubulidentata are known. Unlike ...

Pygmy gerbil The pygmy gerbil (''Gerbillus henleyi'') is distributed mainly in Algeria to Israel and the Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , " ...

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 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 lightweig ...

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 Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forcep-like pincers on their abdomen, and membranous wings fol ...

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 A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

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 A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

References