Social relationships due to sex, age and morphology in Great Tits Parus major wintering in a mountainous habitat of Central Spain

Social relationships within a Great Tit Parus major population in a mountainous area in central Spain under winter conditions and in two consecutive years were studied. Three hierarchical classes were established using aggressive interactions between the individuals over artificial feeders: dominants, subdominants and subordinates. Sex, age and morphology were found to be factors responsible of the social organisation in the Great Tit. Adult males were the most dominant individuals and juvenile females the most subordinate. Juvenile males and adult females, contrary to prior expectations, were distributed among social classes in a way that did not differ from a random distribution. Individuals in the different social classes differed morphologically, dominants being larger and heavier than subordinates. Morphological differences among classes disappeared when the effect of sex was removed, whereas they remained when the effect of age was removed. Therefore, morphological differences among the social classes were due to differences in sex-ratios among classes. We suggest that sex per se is the main factor responsible for social dominance, although other factors such as a previous link with the area (site relation) or mating with a highly ranked bird (high ranking match) may reverse social relationships

Barluenga, M., Barbosa, A. & Moreno, E., Ardeola 47(1), 2000, 19-27