KNOWLEDGE BASE

This short note reported that Eurasian beavers had returned to Bulgaria, where they had been absent for over 150 years. The beavers were detected in the north of the country and the document contained two photos of the evidence gathered. By publishing this evidence, the authors aimed to inform the public and urge authorities to protect the species and its habitat, having noted that some local residents were harbouring a "negative attitude" towards the animals.

Acquiring a territory and a mate are crucial to beavers' reproductive success. These are often studied as independent phenomena but, for the beaver, they are not so easily separated. Here, scientists studied these phenomena simultaneously in a high-density Eurasian beaver population in Norway. The results showed that territory acquisition in this context depended more on a beaver's competitive ability (i.e. being bigger, or knowing the area better, than the other beaver) than on them being compatible with a potential mate. The text also discussed the reproductive trade-offs related to this dynamic.

Researchers tested whether Eurasian beavers' foraging habits differed according to sex. By following the activities of 41 beavers in Norway, they found that, while males and females spend similar amounts of time foraging overall, females spend more time in the lodge during spring and eat more aquatic vegetation. Males tend to eat more shrubs and trees throughout the year. These differences may help beavers adapt to the needs of reproductive cycles.

This paper describes the use of radio-frequency identification (RFID) technology to monitor beavers. RFID involves using fixed antennae to detect beavers based on microchips implanted, in this case, on their neck. At this site, RFID allowed researchers to monitor beavers without trapping them. For example, they were able to see when beavers were coming in and out of their lodges and dens. Some limitations of this method are also described in the paper.

North American beavers were observed using a hollow tree as a lodge in a Mississippi swamp, a behaviour never previously recorded. They started using the hollow tree in 2016 and eventually built a more traditional lodge around the entrance. When disturbed by researchers, the beavers were also recorded resting in another nearby hollow tree. This paper contained incredible photos of this activity; the researchers suggested that such a network of hollow trees may provide beavers with refugia from predation by local alligators.