Isn't this how bats have evolved though?
I have a vague recollection of reading that most squirrels have evidence of trauma from falling, such as healed bone fractures.
If you go to the Cornell Ornithology Lab feeder cam and scan through the feed at night, you will find flying squirrels at the feeder. They show signs of nocturnal adaptation, another connection to bats.
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We also had a pheasant who routinely visited the garden and one day showed up with a broken leg, that survived for ages before eventually disappearing. Initially he sat quietly in the undergrowth but started hopping around and doing short flights (with clumsy landings). I put out bird seed for him and he incredibly quickly learned to hoot and flap outside my back door when he was hungry. He once followed me into my shed when he was expecting feeding and had to be shoo'd out.
They explicitly added the caveat about the soft ground. There'd be very little opportunity for mouses to become comfortable with jumping from high areas as there'd be very few occasions that satisfy the requirement. If the mouse jumped into a cave and can't get out, it'd starve to death. If it jumped off a cliff and fell into water, it would drown. If it fell off a skyscraper, there'd be Asphalt at the ground etc. Off the top of my head, there are no natural places in which mouses could safely get comfortable with jumping. Thus, they'd only do so if they're in mortal danger. And they absolutely do jump off high places if they're terrified
It could be to avoid getting disorientated though, or to be able to see a predator and reverse course...
I can't imagine why the mice would climb trees, but if they did and fall down, they probably gonna be fine most of the time.
In many forests there is lots of large rocks and steep slope/cliffs/precipice in the range 0-5 m where mice possibly could shorten their path by jumping. But I'd suppose they rather use a path they can go in both directions.
It could also be because they don't like to change their location too fast. You never know where you could end up. When you fall you might fall next to a cat for instance.
It's not how this works, cats are decent swimmers yet they generally refuse to get anywhere close to water…
And then there's the actual vision. Are mice known for being able to see long distance? One could posit, if not then most jumps would be leaps of faith into vague amorphous blobs, full of potential danger and impossible to triangulate or assess.
Why do I wear impractical clothing? I never even thought of it as impractical.
Just because they don't fall super fast doesn't mean they don't get injured because they don't have as much distance to "drop and roll" like a human does.