Eyes open during the second week, and several factors can influence the exact timing. The eyes of kittens born to younger mothers tend to open earlier than kittens born to older mothers, female kittens’ eyes are more likely to open prior to males, and excessively dark conditions hasten eye opening. The timing of eye opening is also heritable (Braastad and Heggelund 1984). Vision becomes the kitten’s dominant sensory guide once the eyes are open.
Early maternal care is another important environmental factor in healthy kitten behavioral development. Kittens separated from their mother and hand reared by humans from two weeks of age were more fearful and aggressive toward people and other cats, more sensitive to novel stimuli, developed poor social and parenting skills, and did not learn as well as kittens raised by their mother (Mellen 1992).
Scruffing is a maternal behavior of grasping the kitten’s loose skin around the neck and shoulders with her teeth. The kitten reflexively goes limp and quiet. This allows the queen to move her kittens to new dens with a lower risk of detection from predators. In free‐roaming situations, a queen typically moves den sites multiple times prior to weaning of the litter. Some cats may retain this limp or trance‐like state reflex into adulthood, but many do not, and scruffing by a human during handling usually induces distress (Moody et al. 2020).
2.5.2.3 Socialization (Two–Seven Weeks)
First described by Bateson (1979), kittens have an important “sensitive” period when individual life experiences can have lasting effects on behavioral, neurological, and sensory development. The sensitive period for socialization to humans is thought to occur between the ages of two and seven weeks of age in kittens. In one series of studies, kittens handled by humans between the ages of 3 and 14 weeks were more likely to approach humans and accept human handling for a longer duration than kittens who were handled after 7 weeks or never handled before 14 weeks of age. Withholding handling until 7 weeks of age resulted in kittens who seemed unafraid of humans but did not choose to remain in proximity to humans after initial contact (Karsh and Turner 1988). Another study found that even if handling is delayed to 5 weeks of age, kittens can catch up by 6 months of age in terms of sociability with humans to those kittens for whom handling began several weeks earlier (Lowe and Bradshaw 2001, 2002). These studies indicate that exposure to gentle handling from humans by 7 weeks of age is critical for a cat to enjoy human contact.
Other studies have focused on the quality of human exposure during the sensitive socialization period. Kittens housed at rescue centers demonstrated significantly fewer signs of fear toward humans when handled for two and five minutes daily from birth to 45 days compared to those kittens who experienced only passive exposure to humans during basic husbandry, such as cage cleaning (Casey and Bradshaw 2008). Kittens handled five minutes daily from birth to 45 days of age were more likely to approach strange toys and unfamiliar people as well as slower to learn avoidance tasks (Wilson et al. 1965). The end of the socialization period (seven weeks) corresponds with further development of the emotional system and fear of novel stimuli. Intraspecific social development has received little research attention, but the timeline presumably parallels that of cat‐human social development (Bradshaw 2017).
The socialization development period also corresponds to a time of exponential physical development. Kittens begin running around five weeks of age and have full coordination by seven weeks (Peters 1983). Air righting, or the ability of cats to land on their feet after falling, is first observed between the third and sixth week of life. Kittens produce ultrasonic vocalizations, and the pitch becomes lower with age. Expansion of the vocalization repertoire and avoidance of agonistic vocalizations begins around four weeks of age. Interestingly, the vocalizations of deaf kittens are louder but otherwise almost identical to those of kittens with normal hearing (Houpt 2018).
Visual acuity and binocular vision continue to develop during this stage. Cats have been used extensively as models for research into the neurodevelopment of the mammalian visual system. From this research, we know proper sensory development requires environmental stimulation. Deprivation of certain visual stimuli during development creates permanent alterations and deficiencies in the visual cortex. For instance, cats raised in environments with only horizontal lines did not respond to vertical stripes because of degeneration of the neurons responsible for recognizing vertical edges (Blakemore and Cooper 1971). Kittens not allowed to visualize their front paws due to placement in dark conditions or in an Elizabethan collar did not develop fine motor skills needed for placement of the paws (Hein and Held 1967).
2.5.2.4 Juvenile (Seven Weeks–Sexual Maturity)
Socialization with humans may continue to improve into the juvenile period, provided the kitten received some handling from humans in the preceding weeks (Lowe and Bradshaw 2001; McCune 1995). This is assumed to be the case with intercat socialization as well (Bateson 2014).
Rapid physical development allows the kitten to become fully independent from the mother during this period. Kittens have well‐developed senses, thermoregulation, movement, and detection of danger by this stage. The weaning process is completed during the juvenile stage, and kittens are fully functioning predators by the early part of the juvenile period. The mother cat initiates weaning by bringing dead prey to the kittens around four weeks of age. As the kittens become more successful at killing prey, she later releases increasingly more mobile prey items near the kittens. Kittens continue to initiate suckling, but the queen gradually decreases the duration of nursing bouts to keep the kittens hungry enough to encourage exploration and hunting behavior. As their motor skills develop, the kittens also follow the dam on hunting trips. Eventually the dam only allows short suckling bouts, presumably for bonding purposes, and weaning of the kittens is usually complete by seven weeks (Bateson 2014).
Weaning age appears to have broader impacts on social and abnormal oral behaviors according to a recent survey study (Ahola et al. 2017). Owners of cats weaned before 8 weeks of age were more likely to report behavior problems than owners of cats weaned in the 12–15‐week range. Kittens weaned before 8 weeks were more likely to show aggressive behaviors than those weaned later. Later weaning was a protective factor against aggression toward other cats as well as familiar and unfamiliar people. The prevalence of abnormal oral behaviors like excessive grooming and wool sucking as well as shyness toward novel objects decreased in the kittens weaned after 14 weeks as well (Ahola et al. 2017; Houpt 2018). Overall, owners of cats weaned before 8 weeks of age were more likely to report behavior problems than those weaned in the 12–13‐week range. Aggression, abnormal oral behaviors, and shyness toward novel objects were shown to be inversely correlated to the age of weaning as well (Ahola et al. 2017).
2.5.2.5 Adult (Sexual and Social Maturity)
The juvenile period ends with sexual maturity. In female cats, this correlates with the first sign of estrus, which can be as early as 3 to 4 months and as late as 12 months of age. Environmental factors such as the time of year born, exposure to mature tomcats, the presence of other female cats in estrus, and increasing periods of light all influence the age of estrus onset. Male domestic cats reach sexual maturity between 9 and 12 months. In free‐ranging cat colonies, however, a male may not become reproductively active until two or three years of age, when full integration into a colony is achieved (Hart and Hart 2014a). Social maturity is the stage of final transition into adult behaviors such as territoriality and aggression and in domestic cats is thought to occur between 36 and 48 months of age (Landsberg et al. 2013).
2.6 Maintenance Behaviors
2.6.1 Play
Play is ubiquitous amongst many genera of animals, and cats are no exception. Domestic cat play behaviors are classified as social, locomotor, predatory, or object play (Delgado and Hecht 2019). It has been widely assumed that play is neuromuscular, social, and
