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You can go to Brilliant.org/SciShow to try out today’s Daily Challenges! [♪ INTRO]. Bears have long had a reputation of being itchy...scratching their backs on whatever vertical surface they can find, multiple times in a day.

But collective research points towards another reason they rub on trees that has nothing to do with an itch they can’t scratch. Instead, they could be using it as a way to communicate, and even possibly using it like a bear version of a dating app. Researchers have proposed many theories as to why bears rub on trees.

Some have thought that they are picking up sap to use as an insect repellent. Others reasoned that females are rubbing themselves on trees as they come into heat. Those theories have been hard to test because bears are solitary and territorial creatures that don’t spend much time in groups.

But, technological advances in recent years have made it safer and easier to monitor their behavior. For example, researchers can set up digital cameras with infrared detectors that start recording when an animal is around. And they can also tag bears with lightweight radio transmitters that communicate with satellites.

Then scientists can pair this information with data from the cameras, to determine exactly when and how often a specific bear is rubbing on a tree. And they’ve found out that bears are using the same trees to rub on for generations, confirming another theory that has been kicking around. Bears are using these trees as a communication tool!

You see, bears have an incredible sense of smell, which comes in handy for finding food but also helps them keep track of other bears. Because through past face-to-face encounters, bears can recognize and remember each other's scents. So bears rub their scent on trees to mark the boundaries of their territory.

Picking up this scent also helps bears avoid each other if they want. Like, if a bear recognizes the smell of a particularly aggressive bear that it tussled with before, it might choose to avoid going in that direction. And new research suggests these trees may even help with mate selection, kind of like a bear dating app!

In a paper published in 2021, researchers in Canada found that brown bears who rubbed on trees more frequently had more mates and offspring. These same researchers hypothesize that female bears use trees to pick out the fittest mate. That’s because the scent of a male bear can tell a female bear a lot about its characteristics and breeding fitness.

Like, if the other bear is a relative, which is a hard pass. The female also gets a sense for whether the male is the dominant bear in the area, with access to the best local feeding spots, or a bear who might not be allowed to visit those prime locations. Bears are also one of several mammals that don’t get pregnant right after mating.

They can delay implantation of the fertilized embryo until conditions are right. For example, if the bear doesn’t pack on enough fat before hibernation, its body won’t allow the embryo to implant at all. So they mate with several males throughout the breeding season before picking the best of the bunch...in a sense swiping left more often than right.

So these bears use trees more like smartphones than scratching posts. And studying bear rubbing spots with the help of new technology lets researchers observe, from a safe distance, the more nuanced bits of bear behavior. And getting a better understanding of this can help guide future conservation efforts.

If we know exactly how they’re using trees for communication purposes, we can protect those areas from disturbances, which is particularly important as human activities increase in bear habitats. If you enjoy learning about topics like this, you might enjoy trying out today’s Daily Challenges from Brilliant. Brilliant offers Daily Challenges covering a ton of topics from science and engineering to computer science and math, along with the context you need to solve them.

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And thank you for watching! [ ♪ OUTRO ♪].