How Did This Happen? Is Your Cat’s Aggression Out Of The Blue?

How Did This Happen? Is Your Cat’s Aggression Out Of The Blue?


While sudden behavior changes can occur in pets, they are generally the exception.  Often, changes are slow and insidious until they are intolerable to the owner. Often, the warning signs that undesirable behavior will erupt go unnoticed by the owner. The pet’s behavior at the time of presentation is a combination of multiple factors including genetics, prenatal experience, health and mothering ability of the queen, learning experience, medical diseases and environment. In this article, we will examine events that could have come together to result in one cat’s current behavior pattern.  

Felix, a 2-year-old male, neutered, black and white, domestic short-haired cat presents to the veterinarian for aggression toward Mr. Kennedy, the male owner. One night, Mr. Kennedy sat down to use the computer and Felix jumped out, piloerect, hissing, and spitting. Mr. Kennedy was bitten severely in the hand when he reached down to pet Felix. Felix had not ever been aggressive toward Mr. Kennedy in the past. Ms. Kennedy is baffled by the “sudden” display of aggression toward Mr. Kennedy and asks, “Why did this happen? Felix has always been fine with my husband.” 

The veterinarian reviews Felix’s medical history. He had been adopted from a cat rescue at 8 weeks of age. He was part of a feral litter that had been caught without the queen when they were 5 weeks old and raised in a foster home until adoption. When he was first presented to the veterinarian at 8 weeks, he had an upper respiratory infection that required two courses of oral medication to resolve.  

While performing a physical examination, the veterinarian asks Ms. Kennedy about Felix’s general disposition at home and about any changes in the household. She offers that he has always hidden from anyone who came to her home and preferred herself to Mr. Kennedy. She could not remember a time when Felix approached her husband for attention. Ms. Kennedy loves Felix dearly and can’t bear to upset him. As a result, Mr. Kennedy always administers Felix’s medications and puts him into the cat carrier for his veterinary visits. In addition, Felix’s social environment had changed significantly when Ms. Kennedy recently began traveling overnight for her job and as a result was not home each evening as she had been in the past.

The veterinarian quickly identifies a number of red flags in Felix’s history which predispose him to unfriendly, fearful and aggressive behavior: 

  1. Felix’s birth into a feral litter whose mother was likely to be fearful and under physiologic stress
  2. A lack of socialization to humans during the sensitive period for socialization (2-7 weeks) 
  3. Fearful behavior (such as hiding under the bed and avoiding Mr. Kennedy) beginning at a young age
  4. Negative interactions with Mr. Kennedy
  5. Recent social environmental changes causing acute stress. 

Feral or free-ranging queens are typically undernourished and fearful of people. In general, fearful queens are more likely to raise fearful kittens, but there is uncertainty as to whether this is a hereditary effect, a learned effect or a result of physiologic stress during pregnancy and lactation.

Pregnant animals who are under high levels of physiologic stress or who are in a state of fear during pregnancy give birth to offspring who have a lower threshold for reactivity and are more emotional. In addition, kittens from undernourished mothers are more likely to have deficits in brain growth and behavior problems. Even later in life, well after a normal plane of nutrition has been established, kittens who were undernourished at a young age are more likely to show decreased learning ability, increased levels of fear and aggression toward other cats and people; increased aggressive play, and more random behavior than normally fed kittens. 

Like most domestic animals, cats have a socialization period. This is a period in which a small amount of positive or negative exposure to a particular stimulus results in a large effect on future behavior.  The reverse is also true. If a kitten is not exposed to a certain stimulus (e.g., people) during that time, it is likely to be persistently afraid of that stimulus. Handling during this time is very important if kittens with other predisposing factors (i.e., genetics, feral queen) are to make good pets. The kitten socialization period is between 2-7 weeks, much earlier than puppies. Much like Felix, most kittens begin their contact with humans late in this period or after it has ended. 

Studies have shown that handling for as little as 5 minutes a day from birth to 45 days reduces fear of humans when compared with a lack of handling. In a study of kittens that were handled daily for the first few weeks of life, the handled kittens opened their eyes earlier, emerged from the nest box earlier and developed their coat coloration earlier. Although it is possible to shape a feral kitten older than 7 weeks of age to be a wonderful pet, it will be much more difficult if the kitten is not handled until after 7 weeks. Kittens that are isolated from humans for the first 4 weeks of life are more likely to be unfriendly to people even if they are from friendly parents. 

Environment, learning, and health status continually shape an animal’s behavior throughout its life. Learning is always occurring whether we are conscious of it or not. Each time that the cat interacts with a person, animal, or the environment, learning takes place. If opportunities for interaction are frequent enough, new behaviors – whether positive or negative — will develop and become a part of the animal’s behavioral repertoire.  This is exactly what happened with Felix and Mr. Kennedy. With each medication administration, Felix’s fear of Mr. Kennedy increased. He became classically conditioned (like Pavlov’s dog) to view Mr. Kennedy as a stimulus paired with fear and discomfort. Although he had never acted out aggressively toward Mr. Kennedy, he did hiss and try to escape (defensive reactions) whenever he approached with medication or a cat carrier.  Mr. Kennedy quickly became paired with negative consequences. Negative consequences, combined with fear and increased arousal (lack of socialization + genetic predisposition) are a recipe for aggression. 

Finally, Felix’s environment had changed drastically. The one person with whom he felt safe was now with him less frequently. The increased psychologic and physiologic stress of this environmental change decreased Felix’s already low threshold for fearful, aggressive behavior. He had begun hiding in the home office where Ms. Kennedy spent the majority of her time when she was home. When Mr. Kennedy sat down at the computer desk under which Felix was hiding, Felix attempted to ward him off by hissing, spitting and becoming piloerect – all signs of defensive aggression. When Mr. Kennedy reached for him (a stimulus that had been paired many times before with negative consequences) Felix acted out defensively and bit him. 

At first glance, it may appear that this is an acute case of aggression, but with closer scrutiny of the history, environment and behavior of the animal it is apparent that the reasons for Felix’s behavior are multifactorial and not acute at all. His behavior had slowly been developing since he was adopted. Although we can’t change the factors which led Felix here, we can alter his future interactions with his environment and the people in it, decrease his level of arousal and reactivity, and use counterconditioning to decrease his fear of Mr. Kennedy. With these changes and some time and effort on his owners’ part, his behavior can be significantly altered allowing him to live peacefully with Mr. Kennedy.