It’s fun to think of pet-to-pet angst as jealous puppies, but I doubt the parents of two-legged kids would put up with sibling rivalry that involves a tooth-and-claw terror campaign. Unfortunately, pet face serious injury if you don't know how to get dogs to get along. Proper introductions help enormously, of course.
More often, the behavior is simply healthy competition. In terms of evolution, competition offered a way for the “winner” to gain the most and thus survive.
Therefore, jealous behavior--more accurately termed competition--could be considered a normal survival mechanism.
Why Puppies Compete
Puppies can compete but still get along well for the most part. The more pets you have, though, the greater the chance of pet rivalries getting out of hand. It’s a numbers game—two pets usually love, like, or at least learn to tolerate each other. That’s the situation at my house, where Magic (dog) would like to be buddies and Seren (kitty) keeps the “interloper” in line. Three pets also can get along but often create an odd-pet-out that gets bullied. Four or more pets virtually guarantee serious issues that require management.
Territory, personality, and resources impact whether or not rivalry conflict develops. The most important territory for a pet is YOU (the owner), and access to your attention can be a biggie. Magic becomes quite the pester-bug whenever Seren demands lap time.
Territorial disputes usually arise over arguments about limited resources (food, toys, litter box, beds, and more). Seren shows up to cage treats only when she knows Magic just finagled a taste.
Complementary pet personalities can keep the peace, with a confident in-charge pet not challenged by a laid-back pet personality.
But two wannabe “top dog” types who argue over who’s in charge, or a bully-pet matched to a shrinking violet type can be misery to live with. Thank goodness, in my house the dog knows and accepts that the cat’s in charge—but that doesn’t stop his teasing, just like a human little brother pesters big sister.
The animals’ breed, gender, and sexual status matter. The worst issues seem to arise from same-sex and same-species pets. That is, two girl dogs or two boy dogs (or two female cats, or male cats) seem to butt heads most often. Neutering and spaying can help level the playing field by reducing hormonal stress may stir up rivalries.
When pets are well socialized to other species, dog-cat relationships have the least rivalry because they compete mostly for different resources (different toys, toilets, and beds). Well-adjusted dogs also tend to get along. Cat-to-cat rivalry is most common, especially when a new cat comes into a resident kitty’s home and territory.
What Jealousy Looks Like
There is a range of behaviors that arise from pet rivalry/competition. We think of pet rivalries as being knock-down-drag-out fights—and those can happen, but only when it’s gone too far! Most of these behaviors are so subtle, that owners may miss the silent stare from across the room that controls access to the living room.
Or not understand the dog paw placed on top of a toy—or your foot—that claims ownership.
Owners should become concerned about pet rivalry if/when the behaviors provoke fear and/or risk physical harm to the other pet(s). Pets can indulge in play behaviors that might be mistaken for aggression. You’ll know they're just playing when both parties come back for more, rather than one hiding or running away from encounters. Dogs signal play with exaggerated behaviors (play bow, for example), and may whine and growl and bark during play. Cats play in silence—so vocalizations from a cat mean business.
3 Ways To Reduce Competition
The world of pets is not a democracy. There WILL be a pet that comes out on top—that winner may be different from room to room. Recognize who should be “king” and support him/her.
Usually, that’s the oldest and/or pet that’s been in the house longest, the healthiest pet, or (in a dog/cat household) the confident cat. In other words, your new puppy probably won't get to be "top dog" unless and until he grows up, so avoid giving the baby dog preferential treatment because that can upset the "real" boss pet and prolong rivalry behaviors. Here's what to do.
Give Preferential Treatment to The King Pet. Feed the king first, play with him first, allow access to the best spots (like your lap), and generally let the other pet know the king rules. Then pay special attention to Wimpy when King isn’t around to see or object. For instance, Magic gets special time outside, plus car rides that Seren doesn’t get—but she could care less. In the house, though, she gets priority.
Create a House Of Plenty. That means you provide multiple resources so the pets have no reason to argue over the single bone or ball or the one litter box. Make sure there are LOTS of toys and treats, resting spots and hiding places to go around. If one chew toy causes too many arguments, THROW IT AWAY. Supervise your pets an interrupt problem behaviors rather than letting them go on.
Get Professional Help. If you do have a dangerous situation and have already had or fear physical injury may happen, get professional help! The longer pets “practice” a behavior (even bad ones) the longer it takes to change that pattern.
Veterinary behaviorists, dog trainers, and animal behavior consultants experienced with the dynamics have the expertise to offer very specific help based on the individual pets’ circumstances.