Authors:
Mariela Vargas-Irwin, PSYD, BCBA-D, LABA
Natalia Vargas Medina
Ahmad Al Masarani
Abstract:
Non-human animal models of social behavior are not just interesting in and of themselves as they have implications for animal care and welfare, but also prove helpful when the study of the phenomenon in question in humans is limited due to ethical reasons or would be impossible due to practical reasons.
Sibling rivalry, for example, is an interesting phenomenon, but its research in humans, given obvious practicalities, can only be correlational or observational. Research on sibling rivalry and the psychological impact of a sibling’s arrival highlights a complex dynamic influenced by family structure, temperament, and parenting style. According to anecdotal reports, when a new sibling is born, the older child often experiences feelings of jealousy, anxiety, and insecurity, as they may perceive a shift in parental attention and resources. This can result in rivalry behaviors such as aggression, withdrawal, or regression to earlier developmental stages (e.g., bedwetting).
The present study involved the socialization of two pairs of domestic cats (Felis catus). One litter sibling pair, Pickles and Papaya, was adopted at the age of one year. This was their second home after being trapped in Saint Thomas. The second pair of litter siblings, Pepper and Pitaya, were adopted from Puerto Rico. This was their first home. One of the older cats is ginger, and the other is gray and white. Similarly, one of the younger pairs is ginger, and the other is gray. The four cats are all American Shorthair mixed breed, and three of them are male. Pepper is the only female, and she has two thumbs on her front paws. Pickles and Papaya have been clicker trained.
Following veterinarian recommendations, the younger sibling pair was confined to a bathroom upon arrival at the house. They were exposed to the older cats via visits in a playpen, followed by visits in a gated area, and lastly, full exposure in the entire house. The absence of hissing was reinforced with clicks, praise, and physical contact. Data on hissing, aggression, and emesis were collected. Rates of hissing and emesis showed a decreasing trend, supporting successful integration without the use of the psychopharmacological intervention (anxiolytic feline hormones) suggested by cat experts.
A reversal was conducted when, per veterinarian recommendations, the kittens were confined for one week following spaying/neutering. Results provide a roadmap for the socialization of pairs of kittens and shed light on the importance of gradual exposure and equity in the introduction of siblings to each other.
Background:
It is of particular interest to observe the behavior of small children, up to the age of two or three, towards their younger brothers or sisters. For instance, here was a child who had so far been the only one, and now he was told that the stork had brought a new baby. He looked the new arrival up and down and declared decisively: “The stork can take him away again!” (Freud, 1900/1953, p. 251).
Even though 79% of people in the USA have at least one sibling (U.S. Census Bureau, 2023), and the transition to siblinghood (TTS) has been recognized as a stressful event since Freudian times, there is a relative sparsity of research focused on sibling rivalry. According to Volling (2012), there are only 43 published sources addressing children’s reactions to the birth of a baby sibling. Of the 43 sources, six involved clinical case studies of individual children experiencing difficulties after the birth of an infant sibling. One was a book containing the author’s account of his firstborn child’s reactions to the birth of the second child (Mendelson, 1990). Two books provided overall summaries of findings from specific studies (Dunn & Kendrick, 1982; Stewart, 1990). Eleven studies consisted of qualitative accounts obtained from parent or child interviews or retrospective studies that presented descriptive statistics (e.g., percentages of children who evinced certain behaviors) based on maternal reports of changes since the infant sibling’s birth. Three reviews were also uncovered: one addressed whether popular child care books incorporated TTS research findings (Kramer & Ramsburg, 2002), and two provided narrative summaries of the literature to that date (Murphy, 1993; Vandell, 1987).
In her review of firstborn changes after the birth of a sibling, Volling did not focus on the clinical case studies because it was hypothesized that these children’s behaviors had to be extreme in order to be brought to the attention of a professional. The descriptive, postbirth studies and qualitative accounts were also dropped due to the potential bias of mothers’ retrospective reports, particularly in noting changes in disruptive behavior at a time when they were under considerable duress and fatigue from caring for a newborn. To be included in the final group, actual statistical analyses testing significant changes from before to after the birth or differences across groups (e.g., children with and without a sibling) had to be conducted. This left a total of 23 publications. Seven unpublished dissertations were also included, resulting in 30 sources for this review.
Volling (2012) notes that of the 23 published studies, two were published in the 1970s, 10 in the 1980s, and 10 in the 1990s (see Table 1). From 1997 until 2011, only one study addressing changes in firstborn children’s behavioral adjustment following the birth of an infant sibling was published (Kojima et al., 2005). Of the seven dissertations, three were conducted in the 1980s and four in the 1990s. According to Volling, “despite the continued interest in TTS by parents and practitioners, research has declined substantially over the past decade. The reasons for this noticeable absence of studies since 2000 are not entirely clear. In any event, it is a reminder of how little attention has been devoted in recent years to this significant developmental transition for many young children and their parents” (p. 501).
Volling (2012) points out that, with the exception of the study by Teti et al. (1996), the majority of these studies included relatively small samples (usually between 30 to 50 families, with one study having as few as eight). Many of these studies relied on observational methods in the children’s homes which given its labor-intensity, results in small sample sizes. Most studies also focused on predominantly White, middle-class samples from either the United States or Europe, with the work by Kojima et al. (2005) in Japan being an exception. Far less is known about TTS in other cultures or for different ethnic or racial groups.
The postbirth research designs included studies in which families were contacted at one point after the birth and asked to report on changes in children’s behavior. A second group of studies used longitudinal research designs. These studies generally recruited a sample of women expecting their second children and followed them over time. In most cases, they included one prebirth assessment and at least one postbirth assessment, often conducted 1 month before and 1 month after the birth. These repeated assessments allowed for the examination of changes in problem behavior before and after the arrival of the baby sibling.
A third group of studies included quasi-experimental designs. These studies also used a pre- and postbirth design, but in addition to the group of mothers expecting their second children, there was a matched control group in which the mothers were not pregnant. Children’s behaviors in both groups were then assessed twice, with the sibling group observed before and after the sibling’s birth. The groups were compared to determine if changes in the older children’s behaviors were significantly different in the group experiencing a sibling’s birth versus the matched control group.
A fourth group of studies was labeled natural experiments (Bronfenbrenner, 1979). In this case, an existing longitudinal study of children’s development was being conducted, and over time, the family structure changed such that between time points, some families had a second child (the sibling group), while the remaining families did not (the no-sibling group). Changes in children’s behaviors across the two time points were then compared across groups. In this case, the birth of a sibling was considered to have an effect on the older siblings’ adjustment if change patterns differed significantly between the groups. One limitation of this design is that the timing of the birth could have occurred at any point between assessment periods (e.g., 1 month or 9 months prior).
The fifth group of studies included secondary data analyses from large national data sets where a baby was born between assessment points. Children in these analyses included firstborns and later-born children, so the studies were not restricted to an examination of changes following the birth of a second child. The advantage of these studies is the large sample of children included in the analyses, which allows for both comparison and control. The disadvantage is that the timing of the birth is not always known, and the age and birth order of the children vary.
Given the methodological and ethical challenges inherent in the study of the transition to siblinghood (TTS), it is not surprising that conclusions vary widely and results appear contradictory. Animal models are often useful in these situations, as they allow experimental manipulations and tighter control of stimuli, which would not be possible or ethical in studies of humans.
The question, though, arises: Can the behavior of other social mammals, like cats, be extrapolated to humans?
Behavioral science has been developed precisely on the basis of such extrapolations. In 1901, Thorndike developed the Law of Effect based on his experiments with cats. Skinner also worked with pigeons, and more recently, animal models of empathy and prosocial behavior have been utilized (Cacioppo & Berntson, 1992; Cox & Reichel, 2021; Hackenberg et al., 2021; Blystad & Hansen, 2022).
Research on the social behavior of cats reveals a complex and nuanced picture shaped by evolution, genetics, early experiences, and interactions with humans and other cats. Cats have evolved to live in close proximity to humans and other cats over approximately 9,500 years, becoming more sociable than their wild ancestors. Bradshaw (2016) highlights that domestication has led to the development of social behaviors distinct from those of wild felids, allowing domestic cats to form social groups in resource-rich environments. The early socialization period, particularly from 2 to 7 weeks of age, is crucial for cats to become well-adjusted pets. Kittens handled frequently during this period tend to be friendlier and more sociable with humans and other animals. Bradshaw emphasizes that proper socialization during this period can prevent problems with aggression and enhance sociability. Studies show that cats can form strong attachments to their owners, often showing signs of distress when separated. Domestic cats have adapted behaviors to living with humans, such as purring and kneading, which may facilitate bonding. In feral conditions, cats can live in matriarchal groups where related females cooperate in raising kittens, supporting the development of complex social behaviors.
Winslow (1944) examined the effect of competition on social behavior in cats using a competitive runway experiment. The study found that competition slowed running speed, and aggression was often displaced among losers in a competitive situation. This indicates that competitive scenarios can influence social dynamics and aggression in cats. Van den Bos and de Cock Buning (1994) analyzed the behavior of a group of female domestic cats under laboratory conditions. They found a linear rank order among the cats, with higher-ranking cats emitting more offensive threats and receiving more defensive threats. Higher-ranking cats also engaged in more social licking and received more social sniffing and rubbing. Additionally, higher-ranking cats tended to gain weight, while lower-ranking cats lost weight. These findings suggest that dominance hierarchies can form among domestic cats and influence their social interactions.
Barry and Crowell-Davis (1999) investigated the social behavior of neutered, indoor-only domestic cats in 60 households. Their study found no significant differences in affiliative or aggressive behavior based on gender. However, female cats were never observed to allorub other females, while male/male households spent more time in close proximity. The amount of time the cats had lived together was negatively correlated with the amount of aggression observed, indicating the importance of individual differences and the influence of social familiarity.
Guyot, Bennett, and Cross (1980) examined the effects of social isolation on juvenile domestic cats. Kittens reared without littermates displayed enhanced socially directed behavior and hypergregariousness, while those reared with littermates but without a mother showed retarded social behavior. The study suggests that early social interactions are crucial for developing proper social communication skills, and prolonged separation from littermates can lead to long-lasting behavioral effects.
Turner (2021) reviewed the mechanics of social interactions between cats and their owners. Socialized cats show “friendliness to humans,” influencing human attachment. Cats use visual and acoustic cues to interact with humans similarly to how they interact with other cats. The initiation of social interactions and the initiator affect the duration and quality of interactions. Human behaviors and mood also impact cat behavior, and there are differences in interactions based on the owner’s gender, age, and whether the cat is purebred or non-purebred.
In sum, there is ample evidence to suggest that felis catus demonstrate complex social behavior that can be extrapolated to study the transition to siblinghood.
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