Back east somewhere, I think Missouri, they did a study where they radio tagged Whitails (inside a fenced area) and the hunters. It was something like a couple days before any hunter saw a deer, a week before they saw a buck. If memory serves, they took a hunter to within 10' of a bedded buck that remained unseen.

In Florida, they are trying to get rid of invasive pythons. They radio tagged some and the bios would be within feet of an adult and not see it.

I agree we need proof but absence of evidence is not evidence of absence.