Why do polar bears come close to human infrastructure? The answer is more complicated than we think

As the Arctic warms, some polar bears are spending more time on shore, away from the sea ice habitats they rely on to hunt seals.

As polar bears face nutritional stress due to ice loss, some wonder whether they are being forced to take more risks around humans as they search for food, thereby increasing interactions and conflicts between polar bears and humans. But so far, there has been little research on this relationship.

Between 2011 and 2021, research colleagues and I placed trail cameras at three campsites in Wapusk National Park in Manitoba, and later at the nearby Churchill Northern Research Centre, to understand how often polar bears visited these sites on the west coast of Hudson Bay.

The project began at the invitation of Parks Canada when their new backcountry camps at Broad and Owl Rivers were hosting more bears than they expected.

These camps are located far from the coast to reduce the likelihood of polar bear encounters, so answering this looming question is a top priority.

We investigated whether human activities, the length of the ice-free season (or both) influence polar bear visitation. In approximately 80% of bear visits, our photos show enough animals that we can assess their body condition using an established fat index.

We observed 580 bear visits on camera, mostly between July and November, when bears are known to be plentiful in the area. We found that human presence at the camp and at the CNSC had no impact on the number of black bear visits.

However, the length of the annual ice-free season has a significant impact.

If sea ice melts earlier than normal in the spring, forms later than normal in the fall, or both, the ice-free season could be longer. There was no long-term trend in the length of the ice-free season during our study period, but it did vary significantly from year to year.

We found that the longer western Hudson Bay remains ice-free during the year, the more frequently bears visit our study sites.

Poor body condition is considered an indicator of nutritional stress, and maintaining healthy body condition while fasting ashore is critical to polar bear survival.

However, we found that the longer bears were off the ice, the more likely all bears were to approach our study sites, regardless of their nutritional health, rather than seeing visits from hungrier, leaner bears—which is what we would expect.

This result was unexpected because other studies have shown that underweight polar bears are more likely to attack humans, which is thought to mean that these particular bears would have a better chance of finding food and therefore be more likely to approach or prey on humans.

Instead, what we see is that physical conditions may play a different role. Physical condition may not affect polar bears seeking human interaction, but may affect whether interactions between humans and polar bears escalate.

In other words, if polar bears are around humans to begin with, smaller bears may be more likely to actively try to access human food sources, or even prey on humans, than bears with less nutritional stress.

We were also surprised not to see many lone sub-adult bears in our photos. Other studies also show that they are often the ones most likely to have conflicts with others.

However, these observations are consistent with other studies of this subpopulation. As the ice-free season lengthens on average in western Hudson Bay, cub production and survival rates decline.

Our unexpected results, then, may be because there simply were not many young bears in the population during our study period.

Science and Native Observation

Our results suggest that sea ice loss may not lead to more interactions with humans simply because polar bears are thinner or hungrier, so we need to better understand what causes interactions to deteriorate into attacks.

What does this mean for current approaches to reducing the risk of conflict between polar bears and humans?

Returning to Parks Canada’s original question, the likelihood of bears visiting their campsites does not appear to be affected by anything under human control, but the outcomes of any bear visits that do occur certainly are affected.

Our findings may also help explain why scientific explanations and indigenous and local observations of polar bears interacting with humans vary. The scientific literature has long argued that poor physical condition drives polar bears into northern communities.

However, documented observations from the communities themselves indicate that bears entering the communities are not necessarily in worse condition than expected.

Our findings are more consistent with Aboriginal observations, highlighting how untested assumptions can solidify into accepted wisdom through repetition in the scientific literature. SKS

SKS

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