User:Sarahkwhelan/Burrow

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For other uses, see Burrow (disambiguation).

A burrow is a hole or tunnel excavated into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter, protection against predation and exposure to the elements. They can be found in nearly every biome and among various biological interactions. Many different animal species are known to form burrows. These species range from small invertebrates, such as the corophium arenarium, to very large vertebrate species such as the polar bear. Burrows can be constructed into a wide variety of substrates and 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 this well-developed burrow would be a rabbit warren. Burrows may have multiple entrances and exits, for a variety of purposes. They could be used to provide alternatives when there is an animal blocking one entryway, or to help animals escape if a predator has entered. However, it is uncommon that they are used for escape, as many predators will not chase their prey into burrows.

Types of Burrows
Animals can create burrows using a variety of methods. 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 and the aardvark. Pygmy gerbil 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 will actually make use of burrows built by tortoises, which is an example of simple occupancy. These animals can also be referred to as commensals.

Vertebrate burrows
A wide variety of vertebrates construct or use burrows in many different types of substrate and can range widely in complexity. Mammals are perhaps most well known for burrowing. Mammal species such as insectivora, like the voracious mole, and rodents like the prolific gopher, great gerbil and groundhog are found to form burrows. Some other mammals that are known to burrow are the platypus, pangolin, pygmy rabbit, armadillo, rat and weasel. Some species such as the groundhog can construct burrows that occupy a full cubic metre, displacing about 300 kilograms 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. Burrows seem to be distributed based off of soil type and resource availability. Even Carnivora like the meerkat and marsupials are burrowers. The largest burrowing animal is probably the polar bear when it makes its maternity den in snow or earth. Lizards are also known to create 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 pygmy blue-tongue lizard (Tiliqua adelaidensis) when fighting, as they may fight from inside their burrows.

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 create burrows to live in during the winter season, 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.