Field research is the correct answer.
I can ask them to perform complicated tasks by whispering that task to them, while they are 70 to 100 yards away in the forest at night. They then perform that task. They can't possibly hear me whispering. So they can only comprehend that task by using mental telepathic abilities.
They also like to position themselves in the woods within earshot of my tent. When I wake up in the middle of the night, they will make a noise that I worked out the previous evening, before I hit the sack. They know when I wake up in the middle of the night, even when I do not make any noise. That requires mental telepathic abilities.
I have also caught them eavedropping on my dreams, at home, in the suburbs. Because they slapped the side of the house in the middle of the night, next to my bedroom, at the split second that they did not like the dream that I had.
Case closed. They have excellent mental telepathic abilities. Which is why trail cams and other cameras are so ineffective.