depressed chimps eyes reveal its emotional sorrow and inner sense of desolation

social media facebook post instagram size mobile depressed chimps emotional sorrow sense desolation eyes chimpanzee primate sadness despair hopelessness loneliness misery isolation captivity animal welfare mental health wellbeing behavioral indicators psychological distress nonhuman primates emotions research cognition empathy understanding communication signs expressions visual cues facial body language state observational study ethology primatology zoo sanctuary conservation wildlife