On: 'Glacier mice' baffle scientists

[Jensson]

They tracked the balls for two months, if it was easy to see that they always move X direction during a sunny day they would know. That is likely the first thing they checked, we know that plants can turn to face the sun.

[prvc → Jensson]

Because the terrain is never perfectly uniform, the pattern might not be evident within a small period of time, like one day.