麋鹿
When reintroduced into their habitat, the species could face many problems due to years in captivity. Relaxed selection and reproduction with no environmental pressure may have taken place for Père David's deer, due to captive breeding, which can result in the loss of adaptive anti-predator behavior. It is possible that when fully released in the environment from captivity, after generations of offspring, the species could be unable to retain parasite-defense behaviors like grooming. If the population is reintroduced into the environment with no protection against tick infestation, then they can face major problems if not adapted to that environment. Père David's deer may also become confused by other predators such as tigers, since they are no longer adapted to them. A study was done on members of the species in captivity using the sounds of tigers roaring and dogs barking, and the deer did not respond to the barking of the dogs, but hearing the tiger roar caused the deer to spend more time being cautious after hearing the sound, thus showing that the deer still retained ancestral memories of their previous predator, the tiger.