Typical Cat Behavior Around Birds
Cats are predatory animals with strong hunting instincts. Birds trigger cats’ prey drive since they are small animals that cats would hunt in the wild. Opening their mouths is an instinctive reaction when cats see potential prey.
The Flehmen Response
The mouth opening behavior that cats exhibit when they see birds is called the Flehmen response. This is an involuntary reaction that helps cats analyze scents and pheromones more intensely. When cats encounter an interesting or strong odor, they may curl their upper lip, breathe in through their mouth, and appear to grimace. This allows odor molecules to reach the vomeronasal organ or Jacobson’s organ, which is located above the roof of the mouth and detects pheromones. The Flehmen response likely helps cats identify prey like birds from a greater distance by enhancing their ability to detect faint scents in the air.
As PetMD explains, “When cats wrinkle their noses, hold their mouths slightly open, and curl their upper lips, they are doing something called the flehmen response.” https://www.petmd.com/cat/general-health/cat-sneering-what-flehmen-response
Overstimulation
Cats can become overstimulated by certain sights, sounds, and smells. Seeing birds can overstimulate their prey drive as cats are natural hunters. The sight and sounds of birds triggers their instinct to hunt. This overstimulates the cat and causes an excited reaction. One behavioral reaction cats may demonstrate when overstimulated by seeing birds is opening their mouth wide. According to Chewy, this mouth opening is in part a reaction to the overstimulation of their prey drive.
Mimicking Eating
One common habit cats exhibit when seeing birds is opening their mouths as if they are about to eat their prey. This instinctive behavior stems from a cat’s predatory nature. Research shows that cats instinctively open their mouths wide when they catch prey in order to deliver a killing neck bite. Although pet cats are not actually hunting birds, the sight and sound of birds triggers this innate reaction.
Cats have an evolutionary drive to hunt, even when well-fed. Seeing prey animals like birds, squirrels, mice or insects prompts a cat’s prey drive. Opening their mouth is an instinctive part of their sequence of predatory behavior. So when an indoor cat spots a bird through a window, it often reacts with this hard-wired hunting response.
Some experts speculate that cats also open their mouths mimicking the act of eating as a way to try luring birds closer. Since a cat’s open mouth with no sound could resemble a chick begging for food, this may be an attempt to deceive prey. However, more research is needed to determine if cats exhibit this intentional trickery or are simply responding instinctually to seeing potential prey.
Mimicking Panting
Unlike dogs, cats don’t actually pant to regulate their body temperature. However, when overstimulated or stressed, cats may open their mouths in a panting-like motion. According to PetMD, “If their airways are constricted and they are not getting enough oxygen, they may need to do open-mouth breathing to try to get enough air into their lungs.”
Seeing prey like birds can get some cats very excited. As Greencross Vets explains, “Panting is usually a sign that something isn’t right with your cat. Cats only breathe hard with their mouths open when they are very stressed, extremely hot or have been very active.” The stimulation of seeing a bird may cause a stress response that leads to rapid breathing and panting.
As one cat owner described on Pet Forums, “Hi Everyone, Wondered if I could get some quick advice. I’ve recently bought Da Bird and my cat absolutely LOVES it 😀 Only thing is after playing she pants like a dog with her mouth open…” This demonstrates how play time, especially with bird-like toys, can overstimulate cats and cause them to engage in mock panting behavior.
Vocalization
Cats often vocalize when they see prey that interests them, such as birds. One common vocalization is chattering or chirping, which involves rapidly opening and closing the jaw to produce a rhythmic smacking sound (PetMD, 2023). This chattering is thought to mimic the sounds of prey animals, such as squirrels, mice or birds, and may be an instinctual behavior left over from when cats hunted in the wild.
When a cat sees a bird through a window, they may chatter or chirp out of excitement and prey drive. The cat is stimulated by the sight of potential prey and instinctively vocalizes. However, because the prey is on the other side of the glass and out of reach, this results in frustration for the cat.
Related to chattering is an open-mouthed expression that cats make when highly interested in potential prey. According to the Humane Society (2022), this involves fully opening the mouth, pulling back the lips and panting excitedly. It is thought this mimics the act of eating the prey or panting during an intense hunt. So when a cat sees a bird, they may widen their mouth instinctively to prepare for vocalizing or imaginary eating related to their prey drive.
Scent Exchange
One of the main reasons cats open their mouths when they see birds is to exchange scents. Cats have an organ called the vomeronasal organ or Jacobson’s organ in the roof of their mouth that detects pheromones and chemicals.1 Keeping their mouth open allows more air to pass over this organ, giving them more information about scents in their environment.
When a cat sees a bird through a window or in a yard, it is likely trying to pick up traces of the bird’s scent. Opening its mouth helps amplify any scent particles so the cat can better detect them. This allows the cat to gather more sensory information about the intriguing animal it is observing.
Stress Response
Some cats may exhibit a stress response when they see birds, opening their mouths due to feeling anxious or overwhelmed. Since cats have a strong prey drive and are naturally inclined to hunt birds, the sight of them can create a conflicted reaction. Birds may overstimulate a cat’s senses and activate their hunting instincts without an opportunity for release. This can cause stress as the cat experiences an adrenaline rush but cannot act on their impulses. The open mouth in these situations may be an involuntary reaction to this stress or anxiety. As explained on Quora, “Stress Response: Cats may hold their mouths open when they are stressed or anxious.” [1] The mouth opening allows the cat to release stress through panting, similar to a human taking deep breaths when anxious. With birds, it signals the cat is conflicted and temporarily stressed by being unable to resolve the strong prey drive. While alarming for owners, it is simply an instinctive reaction for cats triggered by the close presence of stimulating prey they cannot reach.
[1] https://www.quora.com/What-does-it-mean-when-your-cat-looks-at-you-with-their-mouth-open
Redirected Aggression
When cats are highly stimulated by something they cannot reach, such as a bird outside the window, they can become frustrated and aggressive (source). Since the source of their agitation is out of reach, cats may redirect this aggression onto owners, other pets or objects nearby instead. This phenomenon is known as redirected aggression.
The open mouth gesture that cats sometimes display when seeing birds could be a sign of this redirected aggression. Since they cannot catch the bird, their hunting instincts get triggered but have no proper outlet. So the mouth opening could signal frustration, overstimulation and impending redirected aggression.
To prevent redirected aggression, it’s best to redirect your cat’s attention when they become fixated on a bird. Try enticing them away with toys or treats to calm them down. If aggression does occur, give your cat space to cool off and do not punish them, as this can make the behavior worse.
Individual Personality
Some cats are more bird-obsessed due to inherent personality differences between cats. Just like humans, every cat has their own unique personality that influences how they interact with their environment. According to the ASPCA, there are 5 main feline personality types: timid, bully, aloof, social butterfly, and attention seeker. Cats that fall into the “timid” and “aloof” categories tend to be calmer and less reactive to stimuli like birds. On the other hand, “bullies”, “attention seekers”, and “social butterflies” are often more energetic, outgoing, and predatory. These personality types are more likely to intensely focus on birds and engage in chattering or hunting behaviors.
A 2020 study published in Scientific Reports analyzed the personalities of over 5,300 domestic cats using owner surveys. The findings confirmed there are significant behavioral differences between cat personalities. For example, “timid” and “aloof” cats were less likely to exhibit predatory behavior towards prey animals. In contrast, the more outgoing and assertive personality types showed much stronger reactions to potential prey stimuli. Understanding a cat’s unique personality can provide insight into why some cats are obsessed with birds while others are calmer and less reactive.
The study cited above can be found at: https://www.nature.com/articles/s41598-020-72638-x