In areas where beavers are found, people often discover piles of branches in formerly unobstructed rivers or streams, forming a log bridge that people can walk across. Who did this good deed? Nobody else but the beavers. Beavers are semi-aquatic herbivorous rodents, with a body length of up to 1 meter and a weight of up to 30 kilograms. They are native to Eurasia and are skilled at using their sharp incisors to bite off branches and build dams in rivers, earning them the nickname of "architects of the animal kingdom". The Chinese beaver, a subspecies of Mongolica, is only found in the valley forests of the Ulungur River basin in the Altai region of Xinjiang, and is a second-level protected animal in China.
Beavers feed on young trees and use shrubs and medium-sized trees as materials for building nests to defend against predators. Beavers disperse during the summer and gather in winter nests, also digging temporary dens. In a nesting area of a beaver family, winter nests are usually distributed around the nesting area, with fewer dens the farther away they are.
Beavers build nests in the middle of the water, with half of the nest entrance above water and half below water. This makes it difficult for terrestrial predators to approach, while allowing them to enter and exit freely. Sometimes, when the water level rises and threatens to flood the nest entrance, beavers have to gnash the "ceiling" to dig out soil and raise the nest chamber. Sometimes, they accidentally gnash the "ceiling" and have to pile up branches and soil on the roof to repair it, forming a ground nest and a new nest chamber. Next time the water level rises, they simply move to the new nest chamber to avoid it. In years of severe drought, when the water level drops, the nests are at risk of being exposed, which is very dangerous. At this time, beavers come up with another idea. They build dams downstream of the nests to form a small reservoir to raise the water level, so that the nest entrance can always stay above water. The dams are built with layers of branches and mud, which are very sturdy and can reach more than 10 meters in length, allowing people to walk on them without any problem. The beavers' ability to actively change and shape the environment is truly impressive.