But are there any recorded incidents of a pet commiting suicide after it's human died?
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Not exactly, but some can become despondent. When a distant cousin on my mother's side passed away, his beloved collie, who was in good health at the time, just went downhill and was gone a few weeks later. They can become depressed just like humans, and depression can lead to physical maladies, some potentially fatal.
I remember a documentary that showed a young monkey (old enough to take care of itself) that got depressed and died shortly after its mother died.