‘Highly predatory’ brown bears switch habitats to exploit reindeer and moose calving periods, research suggests

Bears adapted their home ranges and utilised the landscape to mirror the habitats of vulnerable prey

Research involving conservation experts at Nottingham Trent University, the University of León in Spain and Norwegian and Swedish researchers, found that bears – particularly those identified as ‘highly predatory’ – adapted their home ranges and utilised the landscape to mirror the habitats of vulnerable prey.

Bears can be very efficient predators of new-born hoofed mammals, known as ungulates. One of the those studied killed 38 new-born reindeer one month and 18 young moose the next, the researchers found.

The team used GPS collars on 15 bears and monitored them for two years in Norrbotten, northern Sweden, using proximity collars on more than 2,500 adult female reindeer to alert the researchers to close encounters.

Bears emerged from their six-month hibernation in the spring and when the reindeer calving period started they changed their preference for habitats near to wetlands and coniferous forests to more rugged terrain and higher elevations favoured by reindeer with young.

Once the reindeer calving period ended, the moose calving period began and bears started to select areas preferred by moose, which included being closer to deciduous forests and old clear cuts and avoiding habitats closer to open areas and public roads.

Once calving season ended in the summer and human recreational activities became more common, bears shifted to a diet of berries and moved their habitats well away from gravel roads for the rest of their active season, before returning to hibernation.

While moose are fully wild animals, reindeer are semi-domesticated in Sweden and herding and husbandry is a major activity and part of the culture of the indigenous Sámi people.

Reindeer are susceptible to predation by large carnivores during calving and it is estimated that up to 30% of calves are killed. As well as large economic losses for herders, the loss of calves, especially female, can have a significant demographic impact on populations by reducing potential future mating adults.

Brown bears are ineffective at hunting adult moose and previous research has shown that new-borns make up 36-44% of their dietary intake during spring in south central Sweden.  

The study showed that kills peaked during the reindeer calving periods in May and that bears classed as highly predatory – eight of the 15 – averaged about half a kill a day during the reindeer and moose calving periods.

Bears regularly killed more than 20 new-born reindeer and five new-born moose in a calving period, the study showed, with one bear averaging about three kills every two days.

The researchers say that some bears will be more aggressive and bold than others and that the predictable behaviour of female reindeer using the same calving sites each year may have been learned by predatory bears. They say their findings could help to develop forecasts of potential hotspots and conflict and establish possible preventative actions.

A varying number of bears are annually culled in response to depredation on reindeer and their calves. 

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

He said: “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.

“Large carnivores are partially recovering their former ranges across multiple continents and, while this can provide ecological benefits for many ecosystems, it can also bring management implications and undesired effects such as depredation of livestock. Our work could help to inform managers and livestock owners how to reduce this conflict and promote long-term conservation and human-wildlife coexistence.

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

Co-author Andres Ordiz, a conservation biologist at the University of León, said: “Our study shows the differences between individual bears’ predatory behaviour and how this helps to explain individual variation in their habitat selection. Differences among individuals are also important from a management perspective, for instance mere predator removal, without targeting specific individuals, may not necessarily reduce conflict.”

The study, which also involved the Norwegian University of Life Sciences, the Norwegian Institute for Nature Research and the Swedish University of Agricultural Sciences, is published in the journal Diversity.