Signs of grief have previously been reported across many species, including great apes, whales, dolphins, elephants and birds.

Among the canid family, there were some prior indications – some wild wolves have been reported burying the carcasses of two-week-old pups, and a dingo mother had been observed transporting its deceased pup to different locations in the days following its death.

But the evidence was overall sparse and, when it came to domestic dogs, confined to anecdotal reports from owners, which run the risk of anthropomorphism and overstating the case.

The new study, published in the “Nature” journal “Scientific Reports”, involved a survey completed by 426 Italian adults who owned at least two dogs, one of whom had died while the other was alive.

Negative changes were reported by 86% of owners, with a quarter saying these lasted longer than six months.

These behaviours included more attention sought (67%), reduced playfulness (57%), and decreased overall activity (46%).

Surviving dogs also slept more, became more fearful, ate less, and whined or barked more.

The researchers found that the length of time the two dogs had lived together was not an important factor in determining grief – rather, what mattered was the quality of the relationship the pair had shared.

How much the owner felt the loss also played a significant role, suggesting that the surviving dog was also responding to the human’s emotional cues.

“This is potentially a major welfare issue that has been overlooked”, with better understanding of behaviour patterns key to meeting the animals’ emotional needs, the authors concluded.