Why did the bear cross the road: A study in American Black Bear stress levels when crossing roads

Imagine that you lived on one side of a park and all of your family and your favorite restaurant were located just across the park. You would probably get used to walking across the park all the time to get to the other side. But what if one day, the park is replaced with a busy highway? You would probably be pretty stressed about crossing it!

This is probably similar to how many modern bears are feeling about the ever increasing number of roads and vehicles in their spaces. A group of researchers in the Department of Fisheries, Wildlife & Conservation Biology at the University of Minnesota, led by Mark A. Ditmer, set out to study this problem and stress levels in American black bears (Ursus americanus) crossing roads. Ditmer has conducted many research projects on American black bears in the past as well, including one assessing how drones affect the stress levels of bears.

An American black bear stares at the camera

The researchers chose to focus on the links between stress and elevated heart rates. In order to see if bears became stressed at road crossings, they wanted to know if their heart rates would change when they approached roads. If that was the case, they also wanted to see if bears got used to roads and were less stressed, if traffic or time of day affected stress, or if bear gender would affect stress. The researchers were also curious how far away from the road a bear could be before becoming stressed.

Using bear tracking technology, heart rate monitors, and detailed maps of all the roads in three specific areas within northern Minnesota (Chippewa National Forest, Camp Ripley, and northwestern Minnesota), the researchers were able to track a wide range of different bears’ heart rates as they approached different roads.

The researchers found that bears experienced a significant increase in heart rate when they got closer to roads and that, for slightly over half of the monitored bears, the heart rate increase was also related to traffic volume. Bears were more likely to cross busy roads at night and less busy roads during the day. It’s almost like the bears are saving up all the busy roads they have to cross until night time, when there are probably a lot fewer cars driving by! Researchers found that bears started to have elevated heart rates on average 73 meters from the road. Although the article doesn’t talk about bear senses, it is likely that this is about when the bears start to figure out that there is a road in front of them. The elevated heart rates could also have been due to many other factors, like time of day, season, landscape, and movement.

Studies like this one are important in helping us learn more about how species, including American black bears, are responding to developing human pressures. Bear heart rates could be a sign that the bears are learning about possible dangers and may eventually come up with alternate routes. This could allow these bears to share more space with us.

These bear cubs are so used to roads that they have stopped to play in the middle of the road, despite medium amounts of traffic [2]

Unfortunately, as the researchers point out, just because some bears are being vigilant does not mean all bears are paying attention, and even some bears with elevated heart rates were still hit in the roads. Some bears chose to venture out onto the side of the road in search of food or easier paths to walk down, despite the obvious dangers. One bear in particular, who spent two years being studied, crossed the road on average every day and a half and maintained an elevated heart rate during every road crossing. In the end, she was still hit and killed by a vehicle.

Some places have developed systems for animals, like natural road overpasses or underpasses, so that they can safely cross over a road, but many areas don’t want to pay for additional construction or they simply may not be feasible given the current infrastructure. Humans and bears need to keep working together and develop even more innovative ways to make sure that the joke can end with the bear getting to the other side of the road safely.

References:
Ditmer, Mark A, Spencer J Rettler, John R Fieberg, Paul A Iaizzo, Timothy G Laske, Karen V Noyce, and David L Garshelis. 2018. “American Black Bears Perceive the Risks of Crossing Roads.” Behavioral Ecology 29 (3): 667–75. https://doi.org/10.1093/beheco/ary020.
“American Black Bear.” 2018. Wikipedia. https://en.wikipedia.org/w/index.php?title=American_black_bear&oldid=857285230.
Greenfieldboyce, Nell. “Drones Increase Heart Rates Of Wild Bears. Too Much Stress?” August 13, 2015. (NPR.Org.) Accessed September 21, 2018. https://www.npr.org/sections/alltechconsidered/2015/08/13/431982136/drones-increase-heart-rates-of-wild-bears-too-much-stress.
van Inelveld, Renee. ”Wildlife Corridors: A Solution to Ending Roadkill? | Finding Porpoise.” March 2, 2015. Accessed September 24, 2018. https://wp.natsci.colostate.edu/findingporpoise/wildlife-corridors-a-solution-to-ending-roadkill/.
“Wildlife Crossing.” 2018. Wikipedia. https://en.wikipedia.org/w/index.php?title=Wildlife_crossing&oldid=851261193.

Media Credits:
[1]: Photo by Valerie. https://flic.kr/p/HiAt7n
[2]: Video by DailyPicksandFlicks. https://youtu.be/C89zQ-42RsE

1.