Brown rats dig well, and often excavate extensive burrow systems. Being able diggers, they can excavate a burrow for shelter in only minutes. Most excavate burrows in which to lay their eggs. They use their sharp incisors to gnaw food, excavate burrows, and defend themselves. Usually, pileated woodpeckers excavate their large nests in the cavities of dead trees. They do not excavate their own nests. The mouthparts are often used to excavate tunnels into grains. This makes the site difficult to excavate and interpret archaeologically. Hydraulic mining developed from ancient Roman techniques that used water to excavate soft underground deposits. Unusually for nuthatches, all five species excavate their own nests. Woodpeckers live in tree cavities they excavate in the trunk. For the most part toucans don't excavate nesting cavities, although some green toucanets do. Flickers excavate larger holes higher on the stem compared to Gila woodpeckers. Large drills are used to sink shafts, excavate stopes, and obtain samples for analysis. The decision was then made to destroy the impression in order to excavate underneath.