Anyone who has watched Chimp Eden (and if you haven't, what are you waiting for?!) knows this.
OMG, I never even cared that much, or knew that much about chimps before that show but I learned so much.
speaking of which- it needs to be renewed for a 3rd season!
On another note, I think all dog owners know that dogs grieve as well. I have so many stories to prove it. For example, I adopted a puppy when I was 18, but he was not suited to living in an apartment. For 2 yrs, I did my best to give him exercise (coming home from work on lunch breaks to walk him, etc.) and stimulation but it wasn't enough. Eventually I realized he needed a huge area to run in and playmates, and my parents took him in. It broke my heart, but he has thrived there, where he has a few acres to romp on with other dogs.
Yet whenever I visit, he always remembers me, despite being away for 5+ yrs. At night, he won't sleep anywhere but at the foot of my bed. And when I visit and then leave, my parents have to leave my (former) bedroom door open for weeks bc he'lll scratch and scratch and scratch until let back in. he pulls all the sheets and blankets up to make a nest and sleeps there for about week. He does this everytime I visit. Breaks my damn heart.

i never meant to make the lil guy so sad.