Crypsis is an entity’s ability to avoid detection. It can be a predator’s ability to avoid being spotted by prey, or prey’s ability to avoid being spotted by predators, or, in this case, an animal’s ability to avoid being spotted by biologists. Although I know it’s a valid term for a behavior, I can’t help but admire the ability of biologists to make their own failure to find an animal into a recognized property of the animal.