PRIOR RESIDENCY AS A KEY DETERMINANT OF SOCIAL-DOMINANCE IN THE WILLOW TIT (PARUS-MONTANUS)

We studied how age, body size and prior residency affected social domi nance in the willow tit (Parus montanus) groups. The contribution of e ach variable was experimentally tested in unisexual two-bird trials, i n which the birds were matched for all variables except the one studie d. Large birds were dominant over smaller ones (Fig. 1). The effect of body size was more prominent in males than in females. Age had no inf luence on dominance. Residents became dominant more often than newcome rs (Fig. 2). Adulthood or larger body size did not override the advant age of prior residency (Fig. 2). Therefore, the proximate reason for t he age-dependent dominance seen in natural willow tit flocks is most l ikely the prior residency advantage of the adults. Factors connected w ith fighting ability (body size and age) seem to be less important tha n the time of establishment of rank, which may reflect the importance of resource value differences between residents and newcomers in this context. The advantage of residency might make it advantageous to be a member of a flock even as a subordinate, rather than being solitary.