Cats and dogs are said to be mortal enemies, but felines grieve the loss of a canine companion, scientists have found.
Mourning is a well-known phenomenon in the animal kingdom, including in humans, cetaceans and primates, but little is known about how our most popular pets cope with loss.
Researchers have long known that the loss of a beloved pet can cause physical pain and mental anguish to humans - now they know cats also struggle with the loss of a fellow pet.
The findings challenge the belief that cats are more aloof and antisocial than dogs, who are also known to mourn lost companions, the scientists say.
Data from questionnaires given to owners of more than 450 cats who had another pet, either a cat or a dog, that died recently reveal the surviving cat sleeps less, eats less and hides more.
Cats also vocalised more when grieving, and sought comfort from their owners more, data show.
"They engaged less in sleeping, eating and playing but more in seeking attention from humans and other pets, hiding, spending time alone and appearing to look for their lost companions," study authors from Oakland University in the US write.
The study indicates that cats endured more severe grief the longer they lived with their fellow pet, but family connection, witnessing the death, and number of pets in the home did not have an impact.
"Time that companion animals spent together engaged in daily activities predicted greater grief-like behaviours and fearfulness, while more positive relationships between the surviving and deceased animals predicted decreases in sleeping, eating and playing," the scientists write.
"The length of time the animals had lived together predicted increased attention-seeking behaviours in the weeks and months following the companion's death."
There was no difference in how a cat responded depending on if it was a cat or dog that had died, the scientists say, which speaks to how the old enemies often live harmoniously side by side, despite communicating in different ways.
The scientists say that the results of the questionnaires indicate that cats "respond to the loss of their animal companions", but warn the signs of grief reported by the owners could actually be the human's own grief being projected on to the animals.
"Our results are consistent with the idea that cats may experience the loss of companion animals in ways similar to what dogs experience despite having evolved from a less social ancestor and may contribute to shifts in our conceptualisation of cats as asocial and aloof," the authors write.
The study is published in the journal Applied Animal Behaviour Science.