The European beaver has also reached the Tagus River. Researchers from the Center for Animal Studies (CEA), a group of zoology professionals, have confirmed its presence in the area of Zorita de los Canes and Almoguera, in the province of Guadalajara.
Marco Ansón and Celia García Prendes have recorded the discovery in an article published in Galemys. Spanish Journal of Mammalogythe official magazine of the Spanish Society for the Conservation and Study of Mammals (SECEM).
They came across evidence of the presence of the rodent while carrying out field work in a large area in the Alcarria region. “There is a wide biodiversity there and we decided to dedicate part of the work we do at the Animal Studies Center to researching vertebrates, including mammals, reptiles and birds,” explains Ansón.
In this part of the province of Guadalajara, biodiversity is favored by the richness of habitats that range from agro-steppes, oak and kermes oak forests and the banks of the Tagus River itself. “We were lucky to see a specimen. “We were able to register it as the first in the Tagus basin.”
At the beginning of this year 2024, its presence had been detected in the Guadalquivir River, in Jaén. It was the third place in Spain where specimens have been found recently. “At the beginning of the 21st century, in 2003, beavers were reported for the first time in Spain after more than a millennium. “He had disappeared.”
They first appeared in the Ebro River. “It was discovered that a population of 18 individuals had been illegally released into this basin. They tried to eliminate them, but it was not successful and it is currently cataloged as a protected species, in the list of wild species under special protection regime.” Later they reached the Tormes River, in the Duero basin, through the same system.
In the case of the province of Guadalajara, after months of monitoring, says this doctor in Paleozoology and specialist in vertebrates, “the hypothesis is that there may be up to three families of this species. “It is possible that they have the colonizing capacity to disperse along the river, even if they find prey along the way.”
They did not arrive in Guadalajara by chance. “The beavers have come in a van,” the paleozoologist ironically says. “We hypothesize a natural dispersal from the other areas, but given that these animals have no way of arriving from the Ebro and that their presence in the Douro is close to Portugal, it is not possible.”
“I’m not saying that the beaver is not all-terrain and can move out of the water to disperse for many kilometers because the animals are surprising, but it seems strange to me in such an anthropized environment today. It is more likely that someone has moved it.”
Marco Ansón believes that this thesis is “more consistent” with the fact that, based on the population in the Ebro River, others appeared in the Duero and the Guadalquivir. The reason may lie, he says, “in a personal fantasy for beavers to spread throughout the country.”
The Eurasian beaver (Castor fiber Linnaeus) is the largest rodent that has inhabited Western Europe. There are specimens that reach 30 kilos. “Few people know that there is a species of European beaver, different from the Canadian beaver. The same thing happens with the lynx.”
It is not easy to see these types of rodents. “They are nocturnal and elusive.” They choose aquatic areas to live, occupying rivers and wetlands, in areas with slopes where they can build their burrows and feed on plant matter.
Marco Ansón and Celia García Prendes have been studying this beaver population since the beginning of last summer. The first indications suggest that their diet will be “seasonal”, taking advantage of different resources depending on the time of year, and thus avoiding food dependence.
In Spain the beaver can have positive effects, the problem is that here we do not give scope to natural spaces because we always try to extract economic benefits from them. In fact, in our country, riparian forests do not exist.”
What will be the impact on the colonization area? “Beavers are engineering species, they affect the habitat in which they are found,” says this specialist in vertebrate diversity. He gives as an example what happened in the North American park of Yellowstone. There the beavers and wolves managed to change the landscape. “In Spain it can have positive effects, the problem is that here we do not give scope to natural spaces because we always try to get economic returns from them.”
In fact, remember that “in our country riparian forests do not exist and it is something that has been criticized a lot as a result of what happened with DANA.” What is unknown is how it may affect the rest of the biodiversity. “It would be interesting to carry out studies in the Ebro, which is where they are most widespread. It is true that our river spaces are so degraded and so full of invasive species released for recreational fishing, that the damage has already been done.”
Until a few years ago there were no beavers in the Iberian Peninsula. There are fossil remains of the species that date back to the Pleistocene and Holocene, but what experts are not very clear about is when it disappeared. “The European beaver became extinct in historical times, probably due to human pressure. In Roman times there were still wild beavers, but there are not many remains and their exact distribution is not well known.”
Marco Ansón cites José Antonio Riquelme, from the Department of Prehistory and Archeology at the University of Granada, who in 1995 published an article describing the discovery of beaver bone remains “from the Iberian period” in Ronda (Málaga). The bones had evidence of cuts and it is believed that at that time humans consumed beavers.
“Now we are working to better understand the species in this area of Alcarria, next to the Tagus River, and delimit its distribution. They are born survivors, I would like to know what kind of pressure they suffered to become extinct.”
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