Domestic cats (Felis silvestris catus) can live in high densities, although most feline species are solitary and exclusively territorial animals; it is possible that certain behavioral strategies enable this phenomenon. These behaviors are regulated by hormones and the gut microbiome, which, in turn, is influenced by domestication. Therefore, we investigated the relationships between the sociality, hormone concentrations, and gut microbiome of domestic cats by conducting three sets of experiments for each group of five cats and analyzing their behavior, hormone concentrations (cortisol, oxytocin, and testosterone), and their gut microbiomes. We observed that individuals with high cortisol and testosterone concentrations established less contact with others, and individuals with high oxytocin concentrations did not exhibit affiliative behaviors as much as expected. Additionally, the higher the frequency of contact among the individuals, the greater the similarity in gut microbiome; gut microbial composition was also related to behavioral patterns and cortisol secretion. Notably, individuals with low cortisol and testosterone concentrations were highly tolerant, making high-density living easy. Oxytocin usually functions in an affiliative manner within groups, but our results suggest that even if typically solitary and territorial animals live in high densities, their oxytocin functions are opposite to those of typically group-living animals.

Physical and mental effects stemming from COVID-19 have impacted not only people’s lives but also the lives of their pets, which in recent years are often seen as members of the family. This study aimed to explore the impact of the COVID-19 pandemic in Japan on pets and their owners. Participants reported changes in physical activity and mental health, as well as working conditions and frequency of interaction with pets, before and after behavioural restrictions due to the COVID-19 pandemic. We also asked about their pets’ behaviours using the Feline Behavioural Assessment and Research Questionnaire (Fe-BARQ) and the Canine Behavioural Assessment and Research Questionnaire (C-BARQ). This study showed that most cat and dog owners spent more time at home due to the COVID-19 behavioural restrictions and that the frequency of contact interaction with their pets increased. However, this study showed higher stress-related behaviours (e.g., cats: excessive grooming; dogs: aggression towards owners) among pets whose owners increased contact interaction. Furthermore, owners’ low mental health was correlated with high stress-related behaviours (e.g., touch sensitivity) in pets. The results of this study indicate that the lockdown caused by the COVID-19 pandemic in Japan may have affected not only the lives of owners but also the interaction between owners and their pets, and consequently their pets’ behaviours. Therefore, there is also concern that changes in lifestyle patterns caused by pandemics could form a negative feedback loop between the health status of both owners and their pets.

In humans Homo sapiens, eyeblinks play an important role in communication. Blinks are synchronized between 2 individuals during conversation, with shared breaks between contexts, suggesting that blink synchronization can facilitate the sharing of a rhythm during communication between 2 individuals. In the case of individuals with autism spectrum disorder, whose major symptom is impaired communication, there is no blink synchronization ( Nakano and Kitazawa 2010; Nakano et al. 2011). Therefore, blink synchronization potentially occurs in 2 individuals who can communicate effectively. In addition, blink synchronization is correlated with the degree of synchronization of activity in the right inferior frontal gyrus of the brain ( Koike et al. 2016). It suggests that being in the same physiological state as one’s partner based on similar brain activity could facilitate mutual understanding. Synchronization of blinks leads to effective communication in humans. Recently, it has been demonstrated that blinks have a social function in nonhuman primates ( Tada et al. 2013; Ballesta et al. 2016). It has also been suggested that dogs Canis familiaris and cats Felis silvestris catus use blinks as communication signals with humans ( Kuhne et al. 2012; Koyasu and Nagasawa 2019). For example, Humphrey et al. reported that the approaching behavior of cats increased when the human observer blinked ( Humphrey et al. 2020). While they did not report blink synchronization in the behavioral test, it is possible that synchronized blinks between cats and humans facilitate approach behavior. In this study, the temporal relationships of blinks between dogs/cats and humans were analyzed. The humans had 5 gaze interactions for 1 min with a dog or a cat. The blinks of dogs/cats and humans were recorded during gaze interactions, and we investigated when the human blinked before and after the dog/cat blinked. The effects of affiliation were examined to explore if blink synchronization was associated with affiliation between humans and dogs/cats. We predicted that blink synchronization would be observed between dogs/cats and their owners, who could communicate effectively. Twenty-six dogs and 24 cats participated in this study. We excluded cases that lacked proper recordings, including cases in which more than 30% of the experimental footage did not capture the eyes of dogs or cats or humans, and cases where experiments were interrupted due to stress states in the dogs or cats. We used 7 pairs of dogs and humans and 10 pairs of cats and humans for the analyses ( Supplementary Table S1 ). Detailed methods are described in Supplementary Materials .

Individual differences in the sociality of cats are influenced by inherited and environmental factors. We recently revealed that hormones can make a difference in intraspecies social behavior. It remains unclear whether cat behavior toward humans is modulated by hormones. Therefore, we analyzed the relationship between cat behavior and their basal hormone concentrations after spending time together with human experimenters. In addition, we analyzed the relationship between cat behavior and the timing of when the individual cats began living with a human because the sociality of cats could be dependent on their developmental experiences. The results showed that male cats that began living with humans earlier had more contact with an experimenter. In addition, individual male cats with low testosterone levels were more likely to interact with an experimenter. These findings of this pilot study suggest that the sociality of male cats toward humans is affected by testosterone and the age at which they begin to live with humans.