Siberian jay friendship test : A study on group cohesion

Abstract: Group and family living is an integral part of many animals’ ecology. Thus the behavior became associated with plenty of advantages as well as disadvantages. However, rarely has the actual concept of the group been investigated. Questions such as, “What constitutes a ‘group’?” and “Do the individuals within these ‘groups’ associate with each other frequently enough to actually enjoy the benefits of group living?” are seldom asked. With these questions in mind, the aim of this study was to use Siberian jay (Perisoreus infaustus) individuals in their territories to explore and shed more light on the issue of the extent of group living. A working definition of a ‘group’ was made and subsequently the birds were observed in their natural habitat in northern Sweden during several seasons. Consequently, a pair-wise coherence index (CI) was created to quantify the levels of association between the individuals within each territory in order to investigate which possible factors affect the extent of the observed cohesion. Results of the study indicate that pair-wise cohesion was strongly dependent on the kinship of the birds. Moreover, it was found that the alpha and kin birds had significantly higher coherence values than the non kin birds. Thus, within a territory, it was the alpha and the kin birds that formed the core of the group with the non kin birds being much less associated with the other individuals. This was in contrast to the hypothesis, which predicted alpha birds to form the core of the group solely, with kin birds having significantly lower coherence. Interestingly, no effect of habitat type and season was found on the cohesion of the territorial group. Moreover, further evidence of sub-grouping was found even on the kinship level, thus suggesting yet more complex interplay between group cohesion and the group members.  All in all, with the non kin birds having low coherence values, the study casts light on the fact that even if individuals are present in a territory, they might not necessarily be a tight unit and as such be unable to fully benefit from group living.