[throwaway5752]

It isn't just cats. Elephants mourn as do whales and dophins, dogs, cows, pigs, parrots and other birds, and apes (including humans) among others.

If one has any sort of biology background the silliness of these types of studies is clear. Humans are simply animals, there is nothing distinct about us aside from being further out on the distribution of cognitive ability.

It would be news if an advanced member of animalia didn't experience grief from the death of another. If an animal can enjoy the presence of another animal (as they clearly can) it should be assumed they can mourn their loss.