Biology session

Social hierarchy is one of the most often used terms, to describe the relationships between group living animals. However the bigger the groups are, the bigger the chance is, that the observed structure will not be linear, but network-like. The investigation of dominance hierarchies are interesting, because they are often related with other social behaviour, and regulate the access to different resources. Previous studies on cooperation between female zebra finches (Taeniopygia guttata) have shown, that they help each other in an asymmetric manner. While cooperating dyads developed stable roles (helper and non-helper), and based on these roles birds could be arranged in a linear social hierarchy. In this present study, we investigated, whether this linear structure can be observed in other aspects of social behaviour of this species. The bird’s agonistic behaviour and performance in a competitive situation at a monopolizable food source were analysed from video recordings. We formed two groups consisted of eight-eight individuals of the same sex. Their social ranks were determined using the most prevalent dominance estimating variables in literature, for example the amount of time spent feeding, landing order and the number of monopolization events. We were also interested in the relation of dominance to condition and neophobia. In our study, the dominance relationships were estimated from the ratios of displacements between individuals. The social hierarchy, that were estimated from the above mentioned variables was not linear, but included more intransitive loops.

According to our preliminary results, the landing order was not proved to be a reliable dominance-measuring variable, because it varies highly across observations. A positive, but not in every case significant correlation was found between the number of displacements and feeding time. This may refer to the fact, that it is not necessary for the birds to displace others from the feeder as many times as possible in order to get enough food: less monopolizations for longer times can be as efficient, as a lot of short ones. The negative relation with condition can indicate, that motivation has a very important role in performance at the feeder: the birds had smaller fat-stores showed more aggression towards their opponents and displaced them more often, than vice versa. We could not find any association between neophobia and landing order. According to our preliminary results, the social hierarchy of zebra finches estimated with different methods do not match each other. Our data suggest that, the traditional dominance-assessing methods are not enough efficient in measuring such social structures, as we revealed between zebra finches. They may measure more factors simultaneously, and due to the high variance in performance of the birds they are not reliable in estimating hierarchies.