To my knowledge, the present study is the first to report an interspecies long-term stress correlation based on hair cortisol of dog-owner dyads, however, no such correlation was reflected in saliva cortisol of the same dyads. Unfortunately, the current study is unable to decide who influences whom with regard to the cortisol response correlation within the dyad. Moreover, no significant differences were found in dog or owner hair cortisol levels between the lifestyles, and dog-human dyad hair cortisol levels also correlated positively within lifestyles. This implies that it is not necessarily the lifestyle (pet or competing) that drives the correlation, but rather other factors such as the shared home environment. Furthermore, behavioral synchronization between dogs and humans has been proposed to depend on the dogs’ sensitivity towards human behavior and the attachment bond within the dyad. Therefore, it is not inconceivable to assume that owners’ long-term physiological stress levels might simply be mirrored by their dogs through their continuous interactions.

Analogously to child-parent bonds, dog-owner relationships also include different attachment styles depending on the behavioral responses of the attached individual (dog) upon separation from its attachment figure (owner). A secure attachment is characterized by the attached individual’s ability to explore and engage in play behaviors when in the company of its secure base (attachment figure). In the present study, LC dogs engaged in longer durations of individual play during the reunion phase compared to HC dogs. While not significant, HC dogs tended to have longer durations of physical contact (p = .052) with their owner during the reunion phase compared to LC dogs. This might indicate that LC dogs were more securely attached to their owners compared to HC dogs. During the unsolvable problem task HC dogs scored higher on the principal component ‘Eye Contact’, looked at the owner more often, and had shorter latencies to establish eye contact compared to LC dogs. Additionally, a significant positive correlation between principal component ‘Eye Contact’ and dog hair cortisol levels was found, indicating that ‘Eye Contact’ increased with higher hair cortisol. This could be because HC dogs are more dependent on their owner.

• Hair cortisol levels correlated within dog-owner dyads, which is the first reported interspecies correlation with regards to long-term stress.
• Lifestyle only affected eye contact behaviors, this might be due to the quentity of training dogs received.
• The level of dog hair cortisol could reflect how attached a dog is to its owner.