Beaver

The beavers (Castor) are a genus of semi-aquatic rodents native to North America and Eurasia that are characterized by their broad, scaly tails. This genus, of all those belonging to the Castoridae family, is the only one not entirely extinct, and includes three species: the American beaver (Castor canadensis), the European beaver (Castor fiber) and the Kellog's beaver (Castor californicus), the latter extinct since the Pleistocene. All of them live exclusively in the northern hemisphere, except for some American beavers that arrived in the Argentine and Chilean region of Tierra del Fuego when they were introduced there. Specimens of this species were also introduced in certain regions of Europe. With these exceptions, Castor canadensis occurs only in North America, and Castor fiber in parts of Europe and Asia. Castor californicus ranged across what is now the western United States. Although they are very similar to each other, genetic research has shown that the European and North American populations of beavers are different species; the main difference is that they have different numbers of chromosomes.

These animals are known for their natural ability to build dams in rivers and streams, and make their homes — called beavers — in the ponds created by the dam blocking the flow of water. For the construction of these structures, they mainly use the trunks of the trees that they fell with their powerful incisors. Despite the large number of trees they cut down, beavers do not usually harm the ecosystem in which they live; on the contrary, they keep it healthy, as its dams provide a host of benefits. Among other things, these barriers foster the creation of wetlands, help control flooding, and remove pollutants from the stream. However, in ecosystems that are foreign to them, these modifications to the environment can be harmful, as has happened, for example, with the beavers introduced on the island of Tierra del Fuego in Argentina and Chile.

For hundreds of years, beavers have been part of popular culture and in some cases have had a great influence on the development of human societies. An example of this is its importance in the European colonization of America, since the search for their skins was one of the factors that drove exploration and the subsequent economic development of North America. This was due to the commercial value of their skins and other products obtained from them, such as castoreum. It is also a very representative element of Canadian culture, to such an extent that it is the national animal of that country. Therefore, the influence of beavers is not limited to the economic and commercial sector; it also covers fields as varied as literature, religion and sports.

Morphology

Drawing of the skull Castor fiber.

The black and flat tail of the castors allows them to be easily identified.

Beavers are related to squirrels (family Sciuridae), as they have certain similar structural features in their skulls and lower jaws. They are also closely related to a South American rodent called the nutria. Beavers are the second largest rodent in the world after the capybara, and the largest in the Northern Hemisphere.

These animals continue to grow throughout their lives. The average weight of adults is 16 kg (kilograms), and although specimens over 25 kg are not common, specimens have been found that have reached 40 kg. Females grow to be as large or even larger. than males of the same age, which is unusual among mammals. They are generally about 30 cm (centimeters) high by 75 cm long, not counting the tail, which is about 25 cm long by 15 cm wide; all of these values, however, vary depending on a number of factors, including the age and species of the individual.

The tail is oval and flattened, and is made up of small, black, hexagonal scales. They are juxtaposed and not overlapping, that is, they do not overlap one another. Its body it is covered with a thick fur to which they owe their enormous commercial value; This is divided into two types: one silky and grayish in color, and another much rougher and longer, and of a brown tone. In addition to being waterproof, the fur coat acts as a coat.

Detail of the incisive pigments

They have four very strong and sharp incisors —pigmented orange on the front face due to the presence of little crystalline ferrihydrite in the enamel that hardens them— and thus they can gnaw the wood with which they feed and build their structures. An adult beaver can cut through a 12-inch-thick piece of wood in about 15 minutes with its powerful teeth. Since these teeth never stop growing, it is vitally important that they constantly use them, or otherwise the incisors of the beaver. top would pierce through their lower jaw.

Beavers have webbed hind feet, while the forefeet, covered in blacker hair, are hand-like, each with five well-developed fingers. The toes of their hind limbs, on the other hand, are joined by a membrane. Beavers do not have good eyesight, although they can see underwater thanks to a nictitating membrane, a third, lateral, transparent eyelid that covers their small eyes. They also have good senses of hearing, smell and touch. While submerged, their nostrils and ears are closed to prevent the entry of water. Thanks to its respiratory system, a beaver can stay underwater for up to fifteen minutes without having to come up for air.

Beavers are lissencephalic, meaning they have a smooth brain. However, they have a cerebral cortex that makes them special among rodents. This thick cerebral cortex is what has made beavers stand above all other rodents in terms of intelligence.

Classification

The genus Castor is one of the more than thirty genera classified within the family Castoridae. Since there are more than 2,200 species of rodents, the species in this genus represent approximately 0.13% of the total species that make up the order Rodentia. Beavers are classified within the animal kingdom because they are eukaryotic, multicellular and heterotrophic organisms, with embryonic development and locomotion capacity; on the edge of the chordates, since they have a notochord, which is the main support of their body, and in their case it is the spine; within the class of mammals, since they are vertebrate beings, amniotes, warm-blooded, with mammary glands and hair; in the order of rodents, the most numerous of mammals, since they have two incisors in their upper and lower jaws, which are constantly growing; and within the family of beavers, which includes modern beavers and their primitive relatives, all of them characterized by being semi-aquatic, having webbed hind feet and large flattened and scaly tails.

Species

The genus Castor includes three species: Castor fiber, Castor canadensis and Castor californicus.

Castor fiber

European castor.

American castor.

The European beaver (Castor fiber) lives in the cold regions of Eurasia, mainly in Russia. It is slightly smaller than its American relative. Since ancient times they were hunted, compromising their survival. In some countries where they used to live, such as Spain and the United Kingdom, they were eradicated due to this excessive hunting, and although in the modern era the species is slightly threatened, more and more efforts are being made to restore their populations throughout the world. continent, so the population of this species is increasing. It is estimated that their number is around 600,000 individuals. To collaborate in this repopulation project, some organizations, such as the European Union (EU), and international agreements, such as The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), administered by the United Nations Environment Program (UNEP), is in charge of protecting this rodent.

Castor canadensis

The American beaver (Castor canadensis), also called simply "beaver" in North America, it is the largest rodent in the Northern Hemisphere and has 25 subspecies. It inhabits the predominantly cool and forested regions of Canada, the United States and Mexico. However, the species has also been introduced in other regions, especially Tierra del Fuego and the Scandinavian peninsula. In Finland they have lived directly with European beavers.

This animal is often hunted for its fur. In the early 19th century, hunting wiped out them from much of their original range. Native settlers and early settlers also ate its meat. Much of the initial exploration of North America was driven precisely by the search for the fur of the American beaver.

This species is more abundant than the European beaver and its population is estimated to be between 10 and 15 million, although there may have been ten times that number of beavers in North America originally, before the days of the fur trade. Despite this decline, the species is not considered endangered.

Castor californicus

The Kellogg's beaver (Castor californicus, also called Castor accessor) lived between the Miocene and Pleistocene periods in western South America. North. It was very similar to the American beaver, as it was also semi-aquatic, although larger. Fossils of this species have been found in the United States, mainly in the state of California, and in Mexico.

Differences Between Species

The nose of the American castor is different from that of the European castor.

Although the European and American beavers are very similar to each other—so much so that some have considered them to be varieties of the same species—the two species differ in some ways. Some of these features are morphological, while others are related to their behavior. The main morphological difference between them is found in their nasal bones. Another characteristic that makes the difference is the different number of chromosomes of each species. This fact prevents members of different species of beavers from interbreeding with each other. In the following table compares the most outstanding distinctive features:

Behavior

Illustration of Herman Moll where detailed description of the process followed by the beavers to build their dikes.

Beavers spend most of the time in the water.

Beavers are essentially aquatic in their activities, never traveling on land unless necessary. They are sociable animals, forming groups or colonies of up to twelve individuals, made up of a couple and their young. Small families can live in a single burrow, but larger ones may need additional shelters. The greater the isolation of the where they live and the abundance of food, the larger the beaver population will be.

They live in streams where, in order to get water deep enough, they build dams with mud and the trunks and branches of trees that they fell with their powerful incisors. They generally choose streams whose depth is more than one meter to start their work. In the created pond they build their burrows. During construction, the mud or mud is placed with the front legs and not, as is commonly believed, with the tail, which is used solely as a rudder when swimming and to stay upright when supported on its hind legs. the construction of the dams, which they almost always do at night, the beavers transport the mud and stones with their forelimbs and the wood between their teeth. When swimming, they propel themselves with their hind limbs, which always remain submerged, only their heads sticking out of the water, in order to breathe and see the environment. Despite the fact that they are much more adept at swimming than moving on land, they do not usually reach large speeds; they usually do not exceed 10 km/h (kilometres per hour).

For construction, these animals transport mud and stones with their forelimbs and wood between their teeth. They almost always work overnight. During the spring and summer, they are in charge of gathering the wood reserves that will serve them to feed themselves during their winter rest. They continue to collect food until the end of autumn. During this period they are also in charge of repairing any damage that the burrow or dikes may have, although they usually do not start doing this until the frost begins. It is also during this time when they reproduce; they mate in the spring months, or a little earlier, and the young are born during the summer. In addition, at the end of each autumn they cover their huts with fresh mud, which freezes when the temperature drops in winter and becomes as hard as stone, in such a way that predators cannot disturb their rest. With the arrival of winter, they take refuge in their burrow and subsist on the reserve that they were in charge of gathering throughout the year. When the ice breaks up in spring, they leave their dens and start the cycle all over again.

Predators

The predators that these rodents usually have are the wolf, the brown bear, the black bear, the lynx, the puma, the wolverine and the otter. And sometimes birds of prey.

Territorial defense

Since the territory they inhabit is extremely important to beavers, especially because of all the time they spend building on it, they often defend it against external threats. If a stranger enters the territory of a beaver colony, they will most likely end up fighting him, sometimes to the death. The way they detect the presence of strangers is through smell; if they catch an unfamiliar scent, finding its source becomes a priority, even more important than gathering food, and they do not rest until they have found it. However, beavers are known to be able to recognize specific odors from other families with which they are related, in which case they tolerate them within their territory and do them no harm; the same happens with other species that do not harm them and whose odors, with the passage of time, become familiar to them.

To warn potential invaders, mainly other beavers, they mark their territory with scent marks—made from a mixture of mud and castoreum—in order to demarcate their lands and try to prevent confrontations. They place the scent marks on the fringes of their territory, and the more of them they place, the less likely it is to be invaded, as more marks equals a more powerful colony. The number of marks they place depends in part on season and density of population of the place. During the breeding months, which are January and February, and during the time when young beavers leave their groups and disperse, which is around August, territory marking is increased. Likewise, in an area where there are several beaver colonies, it is common for the number of marks to be high. Territory marking, as well as the defense of it and the repair of dikes and burrows, is carried out by males and females alike.

Food

The diet of beavers is strictly herbivorous. They feed on the bark, twigs, and leaves of felled trees and the roots of aquatic plants. Although they can eat almost any edible vegetable found on the shore of a river or lake, they prefer certain foods over others. It has been observed that European beavers prefer the bark and leaves of trees such as willow, birch, and hazel, while American beavers favor trees such as willow, birch, poplar, cherry, maple, and alder, among others. their preferences, the diet of a beaver is usually based on the availability of food, so they do not reject a food even if it is not one of their favorites.

To survive in the winter, they gather a reserve of food, which they keep submerged at the bottom of the pond where they live, very close to one of the entrances to the burrow. They tend to place the largest branches at the top and the smallest at the bottom of the pile to prevent the latter from being washed away by the current. The colder the climate in which they live, the more important the collection becomes. of this food reserve, since they usually spend practically the entire winter inside their burrows. In addition to serving as a food source, this wood reserve has another function. Since the surface of the pond freezes during the winter, the beavers allow some branches to float in the water, preventing it from solidifying in that area. In this way they can go outside in case of an emergency, for example, if they deplete the food reserve.

Playback

Beavers are capable of mating at almost any stage of their lives, and are monogamous—although if their mate dies, they can get another., it is necessary that both parents collaborate, since one alone would not be able to take care of them. Therefore, they must stay together all the time for reproduction to be successful.

Adult castor with a young specimen.

The mating season begins when the winter ice melts, which is around February. Each pair has only one litter per year. Mating usually takes place underwater, although it can also take place on the bank of the river or pond where the couple lives. After the gestation period, which lasts approximately three and a half months (100 days), the female gives birth. give birth to 2 to 4 pups (although in extreme cases there can be up to 9), which are born with their eyes open and covered with hair. They are suckled during the first weeks of life, in which they remain inside the burrow together with the mother and the young from the previous season, which are around one year old. Two-year-old beavers, if they continue to live with the family, help the mother to feed and protect the newborns. The father, meanwhile, goes out and remains nearby, guarding the territory. As soon as they stop nursing, the mother begins to feed her young with young leaves. When they are very young, the young communicate constantly and make a lot of noise, and as they get older they become less noisy, beginning to communicate with smells or certain specific attitudes. Some time later, usually at one month of age, the young begin to move around the outside of the burrow, although they remain quite dependent on their parents, since they are the ones who continue to administer food and protection for about a year. During this period, they learn some valuable skills by copying the behavior of adult beavers, although they do not yet take part in construction work and other activities. When the young reach sexual maturity, which usually occurs after two years of age, they can separate from the colony and form their own. However, if it is a time of food shortage, drought or there is a high population density, they may postpone their departure, as these factors reduce their chances of successfully establishing a colony. When they finally decide to break away, they usually do not settle very far from their place of birth.

Red flag

Since they spend most of their time in the water or in the safety of their burrows, beavers have few predators. Their main enemies are wolves and humans, followed by bears and lynxes. To protect themselves from them, beavers rely on their sophisticated senses of hearing and smell, as well as warning from their companions. Thus, when a beaver in water is startled, it quickly submerges by vigorously propelling itself with its tail. This produces a loud clap, audible above and below water, which is loud enough to be heard. by a human within a 100 meter radius. This signal serves as a warning to other beavers in the area. Once a beaver has made this alert signal, all beavers in the vicinity submerge and do not come up again. for a while. They may also make this signal in the presence of unfamiliar noises or smells. A beaver is more likely to respond to signals made by older beavers than to those made by young beavers, because the latter have not yet learned when to signal. signal and when not, plus they produce a slightly different sound by having smaller tails.

Geographic distribution

Most of the world's beavers live in North America.

Each species of beaver lives on the continent to which its name refers. The European beaver (Castor fiber), as its name indicates, lives in Europe, although it can also be found in some regions of Asia. Among the countries with the largest populations of this species are Russia, Poland, Ukraine, Belarus, Kazakhstan and the Scandinavian countries, although they extend to nations as distant as France and Mongolia. In the past they came to inhabit almost all of Eurasia, covering all the territory between the British Isles and Russia. From the prehistoric era and until at least the sixth century, this species could be found in the rivers of the north of the Iberian Peninsula, mainly the Duero and the Ebro. However, since its skins and castoreum were highly coveted items, it was hunted throughout the continent, putting its survival at serious risk; in Britain, for example, these animals became extinct in the 16th century. Later, in the 19th century, they could only be found in some swampy regions of Germany, Belarus, Norway, Russia and Mongolia. However, it is currently being reintroduced to many parts of the continent.

For its part, the American beaver (Castor canadensis) inhabits practically all of North America, from Alaska to northern Mexico. In Canada they can be found in all provinces and territories, however, they do not inhabit the northernmost regions, close to the Arctic Ocean. They are also present in virtually all of the United States, except for the desert regions of the Southwest and the Florida panhandle. In the Mexican territory, on the other hand, they are scarce, since they only live in the areas close to the Rio Grande (in the states of Chihuahua, Coahuila, Nuevo León and Tamaulipas) and Colorado (in Sonora).

Fossils of the Kellogg's beaver (Castor californicus) have been found in the US states of Washington, Oregon, Idaho, Nebraska, Kansas and California, and in the Mexican state of Sonora.

Introductions

In order to increase their numbers, specimens of Castor fiber have been released throughout Europe, especially in countries where they used to inhabit or continue to inhabit but their populations have decreased. For example, in October 2005, six European beavers were released in the county of Gloucestershire in Great Britain, and further reintroductions are planned in Scotland and Wales. In Spain, because their reintroduction took place clandestinely and without planning, was not fully welcomed by some, including the Ministry of the Environment of that nation. Its release in other countries, however, has been successful; an example of this are its introductions in Germany —specifically in Bavaria—, the Netherlands and Serbia. They have also returned to the banks of the Morava River, in Slovakia and the Czech Republic.

Some pairs of Castor canadensis were released in the Argentine and Chilean region of Tierra del Fuego in 1946, this introduction being possibly the most important of all, due to the strong impact they have had on the Fuegian ecosystem. This same species was introduced to Finland in 1937 as part of a program to reintroduce the extinct European beaver. After spreading throughout the territory of that country, they reached the Russian region of Karelia. In Poland they were introduced in the decade from 1930.

Land of Fire

Dike in Tierra del Fuego.

Introduced into an area where their natural predators do not inhabit, such as Tierra del Fuego, beavers have modified thousands of hectares of land and are considered an unstoppable plague by the local population. It all arose in 1946, when the Argentine Ministry of the Navy released twenty-five pairs of North American beavers in the northeast of Lake Fagnano and on the banks of the Claro River, located on the Isla Grande of Tierra del Fuego. With the introduction of the species, it was planned to maintain a controlled population to promote the fur industry in the region, since there were no species that could be used for such purposes. It is also said that they were brought to the area by the Argentine navy to be hunted and with their skins they made hats for the officers of the navy itself. However, their attempt to keep the population under control failed, as some of the animals dispersed following the watercourses and colonized the region. Around 1964, reached Chilean lands. They have even crossed the Beagle Channel, as evidenced by their presence on Isla Navarino, and there is evidence that they crossed the Strait of Magellan, as they have been found specimens in the Brunswick peninsula, thus reaching the mainland.

The exact number of beavers living in this region is unknown. Most sources estimate its population to be between 70,000 and 100,000, although some have estimated that it could be as high as 200,000. It is thought that there are approximately 20,000 individuals on Navarino Island alone. In number, beavers have caused serious alterations in the ecosystems of the area, mainly in Chile, where the problem became so extreme that the hunting of ten thousand specimens per year has been allowed to reduce their population, in addition to allowing the sale of their beavers. skins and meat. As a result, between 2004 and 2007 about 11,700 beavers were hunted in Tierra del Fuego. In Argentina, the Legislature of the province of Tierra del Fuego classified the beaver as a "harmful and harmful species" 34;. At first they did not have predators in the area, which greatly influenced their rapid expansion, but over time, the culpeo fox and the puma became their enemies, collaborating with their land. dication. Despite all efforts to stop them, beavers continue to spread, generally to the north, and are estimated to advance at a rate of four to five miles per year. Since 2001, the two countries involved They have begun to cooperate in plans aimed at controlling the beaver population, with the ultimate goal of eradicating them definitively by 2015.

A notable difference between Tierra del Fuego and most of North America is that the trees in the south of the continent do not grow scions, something that does happen with some North American trees such as willows and cottonwoods. Thanks to the offspring, the North American forests are able to regenerate more quickly than the Fuegians. For this reason, the beaver fits perfectly with the forests of its native area, while in the South American region it tends to unbalance the ecosystems. The plant species that has been most affected by beaver activity in Tierra del Fuego is the lenga.

The beaver in Spain

The Ebro Valley or Iberian Basin, where the castors were released.

The Roman historian Apiano tells us about its abundance in the Betis river (Guadalquivir); it existed in all the “important” rivers of northern Iberia, and there are even skeletal remains in Atapuerca and archaeological sites from the VI century. The Swiss naturalist Konrad von Gesner cites the species in Spain as early as 1583, a fact that is difficult to refute, given the unmistakable nature of the species. Therefore, the European beaver is a species of our fauna, hunting and human pressure led this species to local extinction in the Iberian Peninsula in the 19th century XVIII and almost its total extinction in Europe. Several experts agree that the extinction in Spain must have occurred in the 1850s in the Duero basin.

Starting in 2005, a series of indications began to be found that suggested the presence of a beaver population in northern Spain, more specifically in Navarra and La Rioja; such evidence included felled trees, footprints, foraging remains, droppings, and castoreum marks, among others. The beaver had previously inhabited Spain, but disappeared from the area since at least the 17th century due to the rise of weapons of fire, with which it was hunted to obtain its meat and fat. Some time after those indications began to be found, it would be discovered that an environmental group had released 18 European beavers from Bavaria in the spring of 2003 in the Ebro, Aragón and Cidacos rivers. It has been argued that the beavers that appeared in the Ebro were from Russia and that they could have been hybrids of European and American beavers. However, the two species are incompatible for breeding. reproduction and hybrids have never been described.

The reintroduction of rodents sparked an intense debate about the advantages and disadvantages of the return of these animals to the Iberian Peninsula. On the one hand, it was argued that the reintroduction had not occurred naturally, and according to the Spanish Ministry of the Environment, it had been carried out clandestinely and illegally. It was also alleged that the arrival of the beavers could harm the some protected species in the area, such as the European mink and the otter. On the other hand, the defenders of the beavers, among which was a Belgian environmental group called Pays des castors (Country of the beavers), they assured that these animals would bring benefits to the area and its biodiversity, including the European mink. Actually both species inhabit together in some parts of northern Europe, however, their way of interacting would possibly be different in the Iberian Peninsula, since the Mediterranean-type ecosystems present in Spain are very different from the taiga-type ones in the north of the continent and that they are much more wooded. The argument that the presence of beavers could be beneficial for biodiversity was later weakened, since these rodents had mainly damaged the willow and poplar forests, which were precisely the habitat of the European mink.

As the Navarrese and La Riojan administrations considered that the species had arrived clandestinely in the country, the governments of these entities presented the case in June 2007 before the Flora and Fauna Committee of Spain, which consulted the European Commission, since the beaver is a species protected by the European Union. Finally, the Commission considered that the species was outside its natural distribution, so it did not oppose its eradication in the mentioned areas.

Since 1950, beavers have been reintroduced and translocated throughout France from the Bas Rhône basin, into various channels of the Atlantic basin. Translocation efforts have also been carried out in Belgium, Sweden, Finland and Germany. Very it has recently been reestablished in Scotland, where it is a major tourist resource. It is absent only from Portugal and Italy and efforts are being made in all European countries for its conservation and restoration, except in Spain, where efforts are being made to eradicate it.

As indicated in the work Wildlife comeback in Europe: The recovery of selected mammal and bird species, experts currently agree that this species represents a great opportunity to promote the positive ecological effects of the beaver as ecological engineering, including the increase in biodiversity as a result of beaver-induced changes in habitat, and this has been the focus of more recent research. Through the creation of ponds, the beaver increases the amount of nutrients available, which leads to algae and plant growth. As a result, invertebrate species richness is increased and biomass is higher in streams with beaver due to their direct influences and the gaps created by the species.

In Bavaria, 38 dragonfly species were recorded at beaver sites, with 11 directly benefiting from the presence of the beaver species. However, vertebrate species also benefit: fish species double in beaver-influenced habitat, with densities up to 80 times higher than in non-beaver sites.

Greater numbers of amphibian species appeared at beaver sites in the Eifel region and Bavaria, where half of the 12 species directly benefited from beaver activity. In a Russian study on amphibians, productivity was higher in sites with beaver compared to sites without beaver. In addition to this increase in fish diversity and the beneficial effect of the dam on amphibians, beaver habitats provide a greater variety of birds, with more than 50 rare species registered in Bavaria, or an increase, for example, of the black stork (Ciconia nigra) in Central Europe.

There is also evidence that other mammals, such as otters, can use logs cut by beavers as roosting areas, as well as taking advantage of this increased food availability.

More recently, studies have shown a positive effect of gaps created by beavers on insectivorous bats, providing new hunting and feeding sites for species such as Pipistrellus spp.

More generally, beaver can support needed stream restoration in response to climate change and mitigate its effects, such as increased flooding, at extremely low cost.

After a long absence from much of its range, the Eurasian beaver is now slowly reclaiming its role as ecological engineer and keystone species in Europe's freshwater and ecosystems. Undoubtedly, the species will increase more in number and distribution in the coming decades throughout Western Europe, especially in basins where there is no confinement of river sections due to strong artificial barriers that prevent the spread of the species. This taxon must be managed at the basin scale.

The benefits associated with river restoration, and the potential for tourism, are obviously greater than the cost of beaver-related damage. There is a study from the University of Oxford where the economic benefit of restoring the species is highlighted. The peaceful coexistence and mutual benefit of the beaver and man in the Iberian Peninsula must be allowed. See DEINET, S., et al. (2013).

Captive Conservation

American Castors at Smithsonian National Zoo Park in Washington D.C.

In the past, around the middle of the 20th century, when European beaver populations had declined dramatically due to hunting, some beaver specimens began to be kept in captivity for breeding and later released into the wild, in order to re-establish their colonies. These captive conservations were carried out in several European countries, for example, in Switzerland. As populations recovered, releases became less necessary, so now only beavers are kept in captivity for study and display, as in zoos.

In captivity, beavers still need to live in groups. They need an enclosure that has a part of land and another part of water, each of considerable extension (not less than 50 m²), and the water must be deep enough. They remain outdoors all year, although, instead of their burrows, they must have dens in which they can take refuge in the winter.

It is common for them to live longer in captivity than in the wild. In the wild, they have a life expectancy of about ten to twelve years, although they sometimes live up to fifteen, while in captivity they can live up to twenty years.

Habitat

Beavers inhabit riparian zones, and predominantly in cold regions. The habit of these animals for hundreds of thousands of years in their natural habitat has been to keep the aquatic ecosystems in which they live healthy and in good condition., although to a human observer, looking at all the felled trees, it can sometimes appear that they are doing just the opposite. In reality, the beaver is a species that works as a cornerstone in its ecosystem by creating wetlands that are useful for many other species. After humans, no other animal modifies its surrounding environment as much as the beaver.

Dikes

Dike at Lassen Volcano National Park, California.

Dikes are built by beavers to protect themselves from predators such as coyotes, wolves, and bears, and to provide easy and safe access to food during the winter. However, the primary function of this barrier is to stop the flow of the stream, in order to create a pool of calm water where beavers can easily build their burrows. Beavers often build a smaller dam upstream to lessen the force of the current and thus reduce pressure that it exerts on the burrow. They tend to maintain all the structures, with which little by little they increase in size. Beavers can rebuild their main dams in the course of a night, though they may not defend secondary dams as vigorously. Beavers are famous for building very long dams. The longest known was discovered near Three Forks, Montana, and was about 652 m long, 4 m high, and 7 m thick at the base. It is remarkable that these long dams are often the work of only a few related beaver families, and each family rarely exceeds ten members. However, levees are generally no more than 1.5 m (5 ft) high and about 3 m (10 ft) wide at the base, narrowing towards the top. The length of the levee generally depends on the length of the stream itself. In addition to being long, they are usually very resistant, as they can support the weight of a person.

The levee differs in shape according to the nature of the stream in which it lies. Where the water has little force, it is practically straight; where the current is considerable, it is curved, with its convexity facing the current. No particular process has been observed for the building, except that the work is carried out constantly and that all the parts are built with the same solidity.

It is thought that it is primarily the sound of running water that stimulates beavers to build. However, studies looking at the usual activities of beavers have indicated that beavers can respond to a variety of stimuli, not just the sound of moving water. Two experiments showed that even when beavers piled up material near a loudspeaker making sounds of rushing water, they only did so after a considerable period. In one such experiment, beavers were observed to bury the loudspeakers that produced the sound until they could no longer hear it. Additionally, beavers, when confronted with a tube that allowed water to pass through their dam, became commissioned to stop the flow of water by covering the tube with mud and rods. The beavers were observed to do this even when the tube did not produce the sound of moving water. Beavers often repair damage to the dam and build it higher as long as the sound continues. However, at times when rivers become very large, they generally allow small currents to flow freely through the levee.

Trees more than 25 cm in diameter, melted by beavers in one night.

Tree cut and abandoned by beavers, probably because it's too thick.

Beaver dams can be harmful; the flooding they cause can cause extensive property damage, and when flooding occurs alongside railroad tracks, it can cause derailments. Furthermore, if a dam were to break, this results in an instant discharge of water that can also cause damage depending on the force with which it is thrown. This interference is not limited to human geography; beavers can destroy nesting habitats for endangered species, often felling mature trees to no use for the trunks.

On the other hand, the construction of dikes is extremely beneficial for the restoration of wetlands. Other benefits include current control, biodiversity (by providing habitats for many species), purification of water from toxins such as pesticides, and silt retention. Over the eons, this harvesting of silt has produced the fertile soil so sought after by farmers. Levees also reduce erosion and decrease water turbidity, which is a determining factor for aquatic life. Although beavers can cause damage, part of the problem is one of perception. Such damage is highly visible soon after beaver activity begins in the area, while the benefits are long-term and not easily discernible except by someone closely monitoring the area.

Flood Control

A beaver dam has a certain elevation above the water level. When heavy rains occur, the level of the stream rises and the levee gradually releases the extra stored water. Usually this is all that is needed to reduce the height of the flood wave moving downstream, and partially or totally prevents potential damage to human constructions further ahead. In this way, the dike helps to exert some control over flooding. Rivers with beaver dams in their main streams have lower maximum water levels and higher minimum levels, that is, more constant water levels.

When damaging flooding from levees occurs, modern water level control devices can be installed to remedy the problem. Unwanted damage to trees can be prevented by wrapping wire mesh or sheet metal around the bases of the trees.

Creation of wetlands

Dry pond after the break of a dam.

If a beaver pond becomes too shallow due to siltation occurring in it, or if the source of trees dries up, the beavers leave the site. Because it is not maintained, sooner or later the dam breaks and the water drains out. The rich, thick layer of silt, twigs and dry leaves behind the old dam is the ideal habitat for wetland species. Some of those that benefit from the creation of these wetlands are otters, certain waterfowl, and many types of fish. A large part of them will have previously inhabited the edge of the pond. Wetlands have important environmental benefits, since in addition to serving as a refuge for a large number of species, many also use them to feed and reproduce. For salmon, for example, wetlands and ponds created by beavers are very useful., because in them the youngest specimens can hide from their predators and feed calmly. Humans benefit equally, as wetlands provide a valuable source of water for any use, from domestic to industrial to agricultural. In larger wetlands, water can be used for power production in hydroelectric power plants. Due to the large number of fish that inhabit its waters, they are very valuable for fishing activities. Deep wetlands can be useful for river transportation, and some are tourist attractions due to the diversity of landscapes and species that can be seen in them.

Vegas Creation

As a wetland floods and dries up, grass species such as grasses colonize it and it becomes a fertile grassland suitable for grazing. In areas where there is nothing but forest, this provides a valuable site for many animals—moose, for example—that otherwise could not feed themselves. These grasslands are known as vegas, and they are flat, humid and quite fertile areas of land, due to their soils that store water throughout the year. They are also called swamps, this due to the high silt content that they present.

Riparian forest

Dike at the Nenana River, McKinley Park, Alaska, United States.

Eventually the meadow is colonized by riparian trees, for example, aspens, willows, and those species that are favored by beavers. With this having happened, it is possible for the beavers to recolonize the area, and the cycle begins anew.

Nutrient removal

Removing nutrients into the stream, which is done in beaver ponds, is a very valuable process. In a stream, the presence of phosphates and nitrates is normal, as they are part of the eutrophication process, which helps the growth of algae and aquatic plants. However, agriculture carried out near rivers often increases loads. of these and other nutrients in the stream, causing problems downstream when the water is drunk. In addition to silt, beaver dams collect leaves, twigs, and twigs from beaver activities, especially in the fall. The main component of this material is cellulose. Many bacteria produce cellulose, which can be separated from glucose and used as an energy source. Just as algae get their energy from sunlight, these bacteria get their energy from cellulose. However, this source of energy —cellulose— is not enough for their growth. These bacterial populations face a serious shortage of nitroso and phosphorous compounds, so they absorb these nutrients when they come across them in the water stream. In this way, these and other nutrients are fixed in the pond by bacteria and removed from the stream.

Removal of pesticides and herbicides

Agriculture also introduces herbicides and pesticides into streams. Bacteria are an extremely variable group and some of these substances are metabolized and broken down by microorganisms that live in the cellulose-rich bottom located behind a beaver dam.

Denitrification

Castor fire, approximately 6 meters in diameter, in Ontario, Canada.

Another more elaborate hole in Palmer, Alaska.

Some scientists believe that the nitrate cascade, that is, the production of a much larger amount of fixed nitrogen, which in natural cycles can be converted to nitrogen gas, may be just as problematic for ecology as the production of carbon dioxide. carbon. It is likely, though not proven, that beaver dams in a stream may contribute to denitrification, which is the conversion of nitrates (NO₃⁻) to nitrogen gaseous (N₂) and that is only achieved in anoxic conditions (without oxygen).

In wastewater treatment plants, denitrification is accomplished by passing water through successive layers of aerobic and anaerobic organisms. Beneath a beaver dam a similar process occurs. Being in the pond created by the dam, the water seeps into the earth, and there the oxygen dissolved in it is consumed by the fauna that lives in the rich organic layer. At a certain point all the oxygen has been consumed and the earth becomes anaerobic. This step is essential because the presence of oxygen suppresses the enzymatic system that is required for the development of denitrification. This aerobic-anaerobic cycle can occur several times along the stream, and sometimes denitrification results from it. During denitrification, first nitrate is converted to nitrite (NO₃⁻ → NO₂⁻), then later in nitric oxide (NO), then in nitrous oxide (N₂O) and finally in nitrogen gas (N₂). After the whole process, the water returns to the surface. Some genera of bacteria that can participate in this process are: Achromobacter, Alcaligenes, Bacillus, Flavobacterium, Lactobacillus, Micrococcus, Proteus and Pseudomonas, to name a few.

Burrows

Well-maintained dams block the flow of water, thus creating a deep pool that helps insulate the beavers' home: their den, also known as a hut, a structure of Conical shape where the beaver family lives, and which they also build with twigs and mud, as well as interwoven moss and grass. The burrow entrances are underwater to prevent them from being blocked when the pond surface freezes and to make it nearly impossible for other animals to enter (although muskrats have been found living inside burrows along with the beavers that built them).

The burrow itself consists of a main chamber, up to a meter high, whose floor is at water level and where the entrances from the outside arrive, which are usually two: the first, straight and inclined, it is used to bring wood inside, and the second, which descends more directly into the water, is used only to enter and exit. Just outside the first entrance, beavers keep their food stash for the winter. In reality the burrow usually has the floor at two different levels as a protection measure in case the water level rises during the spring thaw. Although air seeps through the walls, it is also common that there is a thinner section in the roof that serves to ventilate the interior and facilitate the entry of air.

Channels

Beavers are very agile and relatively fast when in the water. On the other hand, when moving on land they are much clumsier and slower. This makes it difficult for them to carry the materials they use to build their dikes and burrows, especially logs and branches, to the pond where they live. For this reason, it is common for beavers to build water channels that connect the lagoon with the source of resources they use, for example, a group of trees. Thanks to the channels, they can swim to the desired point, and return to the pond with the materials in the same way. In this way, they significantly reduce the distances they must travel by land, and therefore streamline their work. These channels measure approximately 1 m (meter) wide by 1 m high, and can be up to 100 m long.

Commercial utility

A cup hat made with felt castor skin.

Map of the Hudson River Valley with the drawing of two beavers, proof of the importance these animals had in the development of the region.

Beaver pelts were bartered by Native Americans in the 17th century for European goods. Later they were sent to Great Britain and France, where they were turned into garments. The extensive hunting and trapping of beavers endangered their survival. However, there came a time when the fur trade declined due to its declining demand in Europe and the use of hunting grounds to support the booming agricultural sector. Later there would be a small resurgence in beaver hunting in some areas where there was overpopulation of these animals; although harvesting is usually only done when the skin is valuable, the rest of the animal is usually used as food for other animals as well. The only pelt in North America that surpassed beaver in commercial value was that of the red fox, which was said to be forty times as valuable.

Both beaver testicles and castoreum, a bitter, oily secretion with a slightly foul odor contained in the vaginal (female) or preputial (male) follicles of beavers, have been items used in traditional medicine. In Yupik (Eskimo) medicine, dried beaver testicles were used to relieve pain. Beaver testicles were exported from the Levant (a region where countries like Israel and Syria are now located) between the 10th and 19th centuries. Claudius Aelianus, a Roman author, described beavers biting off their testicles, their organs more valuable, so that hunters would not be interested in killing them. European beavers were hunted to the brink of extinction, partly to obtain castoreum, which was used as an analgesic, anti-inflammatory, antitussive and antipyretic. The Romans even attributed abortifacient properties to the substance. It has also been described that castoreum can be used against dysmenorrhea and hysterical conditions -referring to the uterus-, since it raises blood pressure and increases heart rate. The effects produced by castoreum have been attributed to the accumulation of salicin that beavers receive from the willows that make up their diet, a substance that is transformed into salicylic acid and acts in a very similar way to aspirin. In nature, beavers they use castoreum to mark their territory, although they can also use it to grease their fur in order to protect themselves from external attacks and aggressions. Castoreum was also used in the manufacture of chewing gum, and continues to be used in the perfume manufacturing; It is said that it was Nostradamus who discovered that this substance acted as an odor fixer, a property that was used to make perfumes more durable. However, currently the use of this type of substance is highly controlled, as it is taken into counts the survival of the species.

Cultural influence

Western popular culture often depicts these animals in a positive light, as caring and hard-working characters.

Page Beast of Aberdeen who speaks of the beaver and the íbice.

• The importance of the American castor in the economic, social and political development of Canada through the skin trade led him to his designation as the national animal of that country. It is represented in the Canadian currency of 5 cents and appeared in the first postal stamp placed in circulation in the Canadian colonies in 1849. The pet chosen for the 1976 Olympic Games in Montreal was a beaver who received the name of Amik ("castor" in Algonquin), highlighting the beaver this way as a national symbol. They are also recognized in the heraldic: in the shields of the provinces of Manitoba, Alberta and Saskatchewan, as well as in the shield of Toronto, there are beavers. The castor is also the emblem of many units and organizations within the Canadian Armed Forces, such as the Canadian Military Engineers (Canadian Military Engineers).Canadian Military Engineers).
• In the United States, Oregon is known as State of the Castor. The American castor is his state animal since 1969 and appears on the back of the Oregon flag. It is also the state mammal in New York and appears on the seal of New York City and its flag, this due to the importance of the skin trade at the beginning of the colonization of the region.
• The beaver was already well known and even studied in Europe since at least the Middle Ages; proof of this is his appearance in the Beast of Aberdeena compendium of beasts used to collect information from various animals and was written in England at the end of the 12th century. The Beast of Aberdeen He described the beaver as a gentle animal whose testicles had medicinal properties. He also said that when they were tried to hunt, their testicles were torn to bits to save their lives. By trying to be hunted for the second time, they simply showed their lack of organs and were spared their lives.
• Due to their naive skills, the beaver became the pet of the Massachusetts Institute of Technology, the California Institute of Technology, the University of Toronto and the State University of Oregon. All the sports teams of this last institution are called Oregon State Beavers, and in the same way, the students who study in that school house are known as Beavers. It is also the emblem of the London School of Economics and Political Science and gives its name to the student newspaper of that institution, called The Beaver.
• In the centuryXVIIbased on a question asked by the bishop of Quebec, the Catholic Church ruled that the beaver was a fish in the face of food laws. Therefore, the general prohibition of eating meat on Fridays of Lent does not apply to beef. The legal basis for this decision is probably related to the work Summa Theologiae of Thomas Aquinas, which establishes the animal classification both for his habits and for anatomy.
• The beavers have had great influence on the names of cities and towns, mainly in North America. In the United States there are more than a dozen villages called Beaver (word that in English means ‘castor’). However, influence is sometimes not so obvious. An example of this is Tamaqua, a town in Pennsylvania, the United States, whose name is derived from the word Iroquoise to ‘castor’. In Europe there are also cities whose names were inspired by the beavers. This is the case of Kastoriá, a city located in northern Greece, whose name is possibly related to the importance of the beavers in the local skin trade.
• In some parts of the world the beaver is considered a divine creature because of his abilities. Castors have also influenced the names of geographical accidents. The name of Lac la Ronge, a lake located in the centre of Saskatchewan, Canada, is probably derived from the French word ronger (roer), allusion to the activity of the beavers.
• Mr. and Mrs. Castor (called in English) Mr. Beaver and Mrs. Beaver, respectively) are two important characters in the classic fantasy novel by British writer C. S. Lewis, The lion, the witch and the closet.
• The Bibarel creature of the Pokémon franchise is similar to that of a beaver, and also performs certain activities of the beavers, such as the construction of dikes.
• The Nickelodeon chain transmits The Married CastorsA children's TV show.
• The Toothy and Handy characters in the series Happy Tree Friends They're beavers.