Analysis of factors affecting the behaviour of both dogs during a Strange Situation Procedure (SSP) to assess intraspecific attachment

Previous studies on the dog intraspecific attachment carried out with the Strange Situation Procedure (SSP) have not been able to clarify the nature of this bond. Several factors may affect the behaviour of the dog dyads involved the procedure. In the current study, fifty-five dyads of adult dogs living in the same household participated in a SSP. The duration of fifteen behaviours was measured. Data were analysed using Generalised Linear Mixed Models considering single behaviours as dependent variables. The predictors were episodes (1, 4, and 7), type of relationship (mother-offspring pairs, non-related cohabitant pairs), sex (female-female, male-female, and male-male), and age difference. Bonferroni Holmes post hoc tests were performed to allow pairwise comparison. Dog dyads spent significantly more time trying to escape from the experimental room in episodes 1 (p = 0.008) and 4 (p = 0.029) than episode 7, in passive behaviours in episode 7 compared to episode 1 (p = 0.001), in environmental exploration in episode 1 compared to both episode 4 (p = 0.001) and 7 (p = 0.001), in proximity to each other in episode 4 and 7 compared to episode 1 (4 vs 1: p = 0.001, 7 vs 1: p = 0.001), and in locomotion in episode 1 than episodes 4 (p = 0.009) and 7 (p = 0.001), and in episode 4 compared to 7 (p = 0.007). Mother-offspring pairs spent more time in passive behaviours (p = 0.028) compared to unrelated cohabitant pairs. Male-male pairs spent more time oriented to the door/window compared to female-male (p = 0.030) and female-female pairs (p = 0.030). Finally, proximity to the conspecific decreased (p = 0.040), while locomotion increased (p = 0.027) with age difference. According to our findings, dogs involved in an intraspecific SSP seem to be primarily distressed by the initial separation from the owner. However, they may be able to use the conspecific as a buffer against stress as the test progresses. Other factors related to the subjects involved in the procedure, such as the type of relationship, sex and age difference may also affect their behaviour. Future studies should take these factors into account if they use the SSP to explore dog intraspecific attachment.