Stories of Dogs Mourning for Other Family Pets Shared by Owners Will Truly Melt Your Heart
While dogs may not mourn in the same manner as humans do, studies have revealed that they form emotional connections with their companions, experiencing sadness when they lose them. Even though owners have noticed their pets displaying signs of grief, the phenomenon wasn't formally documented or studied in domesticated dogs until recently.
In a heartwarming discovery, researchers who conducted a survey found that almost 90 percent of dogs who lost a furry friend in the same household displayed signs of grief. As reported by Clare Wilson in New Scientist, these dogs showed changes in behavior, such as decreased playfulness and increased fearfulness in the months following their companion's passing.
They also tended to have smaller appetites and sought more comfort from their human companions. It's not only studies that prove that dogs are capable of mourning the loss of their animal friends.
Plenty of photos and videos circulate depicting dogs waiting patiently by the front door, sitting at the end of the driveway, and even resting near their buddy's gravesite. These poignant images serve as evidence that these animals miss their friends.
Believe it or not, signs of grief can be witnessed in cats, too. And if you want to hear firsthand accounts from pet owners, we've compiled stories from Quora users who responded to the question:
Do dogs mourn the loss of other family pets?
Dogs Will Try to Look for Their Lost Friends
At the very least, a remaining pet will search for the other out of curiosity, then experience a bit of anxious, helpless depression. In our terms, they mope. There is no tool for measuring sadness, but since we know dogs also release the chemical oxytocin, the same as our 'love drug,' except in even larger quantities, we can assume that loss is keenly felt by them.
Because there is now an absence of the drug in them.
This chemical may well be the reason dogs are so friendly and need their buddies. As we've seen, they don't just have dog friends.
Geese, seals, bears, chickens—heck, they get along with lizards, although the feeling may not be mutual. Dogs are just the all-around good guys on the planet.

A Dog's Will
I recently lost my Peach, who was with Mo, my daughter's dog. Mo was never close to me; she was always skittish around me and made sure to keep her distance.
Both dogs are rescued Shar Peis, and both share a house with us.
In Peach's waning hours at the vet, she was brought into the room where we had gathered. The room was small, and we surrounded her to say our goodbyes.
Mo was halfway to the room, sitting down. As I said my goodbye, Mo got up and walked to Peach, and you could see Peach mumbling some words to Mo.
Then Mo moved back to where she was sitting and sat quietly. What I witnessed was my Peach giving the younger Mo instructions to love her grandpa and to take her place when she leaves and her soul moves to meet my parents in heaven.

The Changes After the Dog's Passing
Today, Mo is doing everything Peach used to do. She sits near me, lies down next to me when I am ready for bed, brings me toys when I get home (which she never used to do), and lets me walk her in the morning.
My family noticed when Mo listened to Peach, and now they can’t stop talking about how much closer Mo is with her grandpa.
So yes, they do mourn. I witnessed it.

This Owner Has Witnessed a Cat Mourn for a Family Pet
Yes, and cats do too—we had our lovely staffie (Miska) put down (she was sick), and our cat, after one week, went off food, moped around, and did not really groom or clean himself for about two weeks. We took him to the vet and got a vitamin shot, and were told to give him as much attention as we could and wait. Yes, he came around. So animals (family pets) do mourn.

Staying by Her Friend's Side
Absolutely yes. We had an Old English Sheepdog and a miniature schnauzer that were best friends forever. When the OES died, I buried her in my pet cemetery by the greenhouse with the others.
Every morning when I let Muffy out, she ran to the little cemetery and would just sit there for about half an hour, no matter the weather.
She continued doing this until she passed; now they are both together in the same place, side by side.

Dogs Have Their Own Ways of Mourning
Yes, they do. When I had to put Patches down because she had cancer, her daughter Tekka would go and sit next to her cage.
She didn't eat much for a week. I was watching her reactions.
When I went to take down the cage, she wouldn't get out of the way to let me finish. They were pit bulls, very territorial, but they knew each other was there. When I cried, she wouldn't let me.
But I did see her tear up. Yes, they mourn, but in their own way.

Two Stories of Dog Grief
Oh yes. I have two profound stories. The first was a little poodle.
He was with our cocker when she died. He wouldn't leave her side for many hours, and—I'm being honest here—he never stepped foot in the doghouse they had shared ever again.
He grieved very, very hard for her.
The second was pretty recent. We ended up with a very troubled dog—a corgi-chihuahua mix—who had come from a very traumatic situation. She had so many aggression and other issues that I came very close to taking her to the shelter because all of my other dogs were very gentle and older; she would attack them without provocation and sometimes draw blood.
I had her from three weeks of age; I had never given up on a pet before, and I knew that I'd have to be honest about why I was bringing her in. I was so afraid it would be a death sentence for her. I don't know what happened, but right around the time I was starting to give up on her, she turned a corner and started to bond with us.
One dog in particular, a chihuahua who had been a puppy mill rescue and had lost her bonded buddy, she was particularly fond of. One day, without warning, my nine-year-old chihuahua went to sleep and just didn't wake up.
It was a devastating shock. This corgi-chihuahua mix, who had been such a bully, really surprised me—she kept pawing at my Zoza, trying to get her to get up and play.
She would not let me cover Zoza up. We sat there, side by side, processing our loss together.
She has bounced back a little better than our poodle did, but she had a group of babies I had rescued here and there; the poodle didn't have anyone else, so perhaps that's why. But the corgi-chihuahua has become the mama/grandma to the new babies; she's very gentle and nurturing. Even so, she's not the same; she clearly misses the little dog who was so gentle and had been her friend.

It's heartwarming to know that dogs are capable of establishing friendships that last even after the death of their best buddy. Seeing dogs mourn the loss of their friends shows how deeply they feel emotions and how much they value friendship.
Even in those sad times, you can see how loyal they are to their companions. Have you, yourself, witnessed how a dog mourns for their canine friend?