The possibility that a polar bear somewhere in the Arctic might occassionally be successful at stalking and killing a reindeer (aka caribou) shouldn’t surprise anyone, let alone a biologist on Svalbard. But having video footage of the event makes it immediately newsworthy, especially when the researchers vaguely suggest that global warming might be to blame.
The title of the scientific paper that has generated the latest polar bear hype is called ‘Yes, they can: polar bears Ursus maritimus successfully hunt Svalbard reindeer Rangifer tarandus platyrhynchus’ (Stempnlewicz et al. 2021).
Would any serious scientist really think they couldn’t?
Still photos and video footage were taken by staff and researchers at the Polish Polar Station in Hornsund on 21 August 2020 (see map below) but we are just hearing about it now. Although the paper is referred to as a ‘study’, the document merely puts the 2020 Svalbard event into some kind of biological and historical context by listing other events that were witnessed or where evidence of similar behaviour had been found.
The reason this paper gets any traction at all is not the rarity of the event but because vivid photos were included in the manuscript and two videos included as ‘Supplemental’ material. The kill chase video is included below. Both are found here.
Polar Bears Prey on Reindeer (26 October 2021), taken by station cook Mateusz Gruszka:
The UK DailyMail story played up the climate change angle, even though the paper presents reduced summer sea ice as only one of two options for more polar bears hunting reindeer on Svalbard over the last 20 years: the other option being more bears and more reindeer. Population numbers of polar bears and reindeer in the early 1970s were so low that protections were put in place and surprise (!), numbers of both species are much higher today (Aars et al. 2017; Prop et al. 2015;Stempnlewicz et al. 2021). More bears and more reindeer mean more possible encounters and more potential reindeer kills.
[A few years ago, it was similarly suggested that Western Hudson Bay polar bears were eating more geese and caribou today than they were in 1968 because of a longer ice-free season even though there are many, many more geese and caribou today than there were in the late 1960s.]
I would have added that there are also more people with cameras across the Arctic than there were in the 1970s, which is highly relevant to the current example. More people with smart phones and video cameras means a higher likelihood that someone, somewhere, will capture polar bear behaviour no one has ever been able to document.
As I mentioned earlier this year, polar bears are seldom, if ever, able to successfully chase down an adult reindeer or caribou so the bears usually ignore them; the deer ignore the bears, for the same reason. Watch Western Hudson Bay bears ignore caribou in the video below.
In the 2020 Svalbard instance, however, the bear realized the nearby deer was in a tight space where its only avenue of escape was the sea. The bear was a young adult female in good condition (i.e. not starving) and the reindeer was an adult male, apparently healthy. The bear chased the reindeer a short distance and forced him into the water. She swam after him until she caught him and quickly drowned him. A prolonged chase by the bear was not required.
Reindeer and caribou are good swimmers but apparently not as fast in the water as polar bears. It’s interesting to see how quickly and easily the bear kills the reindeer in the water.
It seems the same bear caught another reindeer in the same manner a few days later but no one witnessed the event. In other words, the bear had learned how to successfully kill reindeer that stumbled into this local trap unaware. Undoubtedly, because they are visual learners, other bears watching this predation event now know how to do it as well. This bear might have figured it out herself but it is just as likely she learned this particular skill by watching her mother (or other bears) doing it.
In this regard, the reindeer hunting phenomenon is similar to the dozens of polar bears at Seal River that hunt belugas from intertidal rocks during the ice-free season in Western Hudson Bay – and to the bears at Cape Schmidt that figured out year ago how to drive walrus off the cliff to their deaths on the rocks below. Once one bear figured it out, many others learn by watching.
Polar bears would not be successful apex predators in one of the harshest environments on Earth if they were not this smart and opportunistic. However, it does not mean that polar bears in general are eating a “more terrestrial diet” because of reduced summer sea ice, as the authors of this paper suggest (a very few bears do; most don’t).
It does indicate that conservation practices initiated in the 20th century that were meant to bolster reindeer and caribou numbers (similarly true for beluga, walrus, and geese) have resulted in more chances for polar bears to be successful in the 21st century despite reduced summer sea ice. Oddly, this seems to have caught some biologists by surprise.
Aars, J., Marques,T.A, Lone, K., Anderson, M., Wiig, Ø., Fløystad, I.M.B., Hagen, S.B. and Buckland, S.T. 2017. The number and distribution of polar bears in the western Barents Sea. Polar Research 36:1. 1374125. doi:10.1080/17518369.2017.1374125
Prop, J., Aars, J., Bardsen, B.-J. et al. 2015. Climate change and the increasing impact of polar bears on bird populations. Frontiers in Ecology and Evolution 3 (33): 1-12. https://doi.org/10.3389/fevo.2015.00033 Open access
Stempnlewicz, L., Kulaszewicz, I. and Aars, J. 2021. Yes, they can: polar bears Ursus maritimus successfully hunt Svalbard reindeer Rangifer tarandus platyrhynchus. Polar Biology 44: 2199-2206. https://doi.org/10.1007/s00300-021-02954-w Open access. Videos are here.