Probability of seeing given wild animal in area

I would like to know how to try to calculate the probability that given individual wild animal is seen on area A when going through it via path, when we know that the animal is indeed in the area and there have been N1, N2, N3.. etc. visitors walking the path and not yet seen the animal. I try to put this in other words: how does the amount of people walking through the path without seeing the animal affect our estimate about probability of seeing it (from the path)?