burrow

thumb|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 interaction types, including symbiosis and competition. Many animal species are known to form burrows. These species range from small amphipods, to very large vertebrate 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 warren.

== Vertebrate burrows == thumb|right|A black-tailed prairie dog, with young, emerges from its burrow 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, amphibians, fish (dragonet and lungfish), reptiles, and birds (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, pygmy rabbit, armadillo, rat and weasel. Some rabbits, members of the family Leporidae, are well-known burrowers. 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 like the meerkat, and marsupials, such as wombats are burrowers. Wombat burrows are large and some have been mapped using a drone. The largest burrowing animal is probably the polar bear when it makes its maternity den in snow or earth. Lizards 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.