I'm a cat lover, and I recently had to say goodbye to my little tuxedo cat, Monkey. Within a week or two his buddy, Kirby, started hiding in the basement, refusing to eat, changing his vocalization patterns. He previously had a tiny little meow like a kitten, and now he was literally yodeling LOUDLY at all hours of the day and night.
I did some research and found that all the traits he was exhibiting were symptomatic of loss and the advice was:
Give him more affection and attention Don't punish his bad behavior Reward him with more affection when he's behaving appropriately Give him time.
I spent a lot of time petting and speaking softly to him over the next few days and I'm happy to say that he's slowly returning to normal. He's spending more time in his usual places and eating much more. The yodeling still hasn't quite stopped, but I'm confident it will over time.
I don't know if I can honestly say it's "grief" they experience, but they do sense a change in their situation and express their emotions much the same way humans do. I thought I'd share this and wondered if anyone else has experienced this sort of behavior.