A number of highly predatory brown bears, including one that killed 38 newborn reindeer one month and 18 young moose the next, have been tracked and monitored in a study in Norrbotten, northern Sweden.

The bear was one of 15 tracked with GPS collars. Researchers also fitted 2,500 adult female reindeer with proximity collars to inform them of any encounters between the two species.

The study – published in the journal Diversity – tracked the bears over two years. They found that many of the more predatory bears had an "active hunting strategy", which involved stalking reindeer grounds during reindeer calving season, before moving to moose habitats for their calving season. During the peak of each calving season, the more aggressive of the bears killed more than 20 newborn reindeer and five newborn moose, respectively. The most effective bear was that which killed 38 newborn reindeer within a month.

“We found that brown bears switched their habitats across pre-calving, reindeer calving, moose calving and post calving periods,” researcher and expert in wildlife conservation in Nottingham Trent University’s School of Animal, Rural and Environmental Sciences Dr Antonio Uzal Fernandez, said in a statement.

“It is clear that highly predatory bears were mirroring the land cover types of reindeer and moose and to overlap with seasonally available and vulnerable prey. Such a process shows an active hunting strategy of brown bears in spring, when their diet is more dependent on animal protein than during the rest of the year."

This wasn't true of all the bears in the study.

“Interestingly, high and low predatory bears selected habitats differently in all study periods with few habitats selected or avoided by both groups,” Fernandez added.

The difference in predatory behavior between the individuals explained the variance in their chosen habitats throughout the year, according to co-author Andres Ordiz, a conservation biologist at the University of León.

"Differences among individuals are also important from a management perspective," Ordiz added. "For instance mere predator removal, without targeting specific individuals, may not necessarily reduce conflict.”

During calving season, the authors say around 30 percent of reindeer calves are killed by predators, while newborn moose make up about 44 percent of the bears' diet during spring in south central Sweden.

The researchers believe that the bears have learned the regular movements of reindeer during the seasons, and hope that this tracking data – and proximity data – could be used to predict potential hotspots for conflict between the two species, and so help, for example, reindeer farmers take preventative action.