SOCIAL-DOMINANCE IN FREE-LIVING WILLOW TITS PARUS-MONTANUS - DETERMINANTS AND SOME IMPLICATIONS OF HIERARCHY

Several features of social dominance among Willow Tit Pants montanus w inter flocks were examined during a four-winter study. Birds of both s exes were evenly distributed over the 33 flocks studied, In nearly hal f of the flocks there was an adult pair accompanied by yearlings, but one-third of the flocks consisted of more than two adults with yearlin gs. Males were found to be dominant over and larger than females. With in a sex, yearlings were usually subordinate to adults, The effect of size on dominance, after controlled for sex and age, remained obscure in our field data. The hierarchical status of an individual was found to rise or at least stay the same in different years, which supports t he ''hopeful dominants'' hypothesis, i.e. birds stay in flocks hoping to achieve a higher status in the future, The ranks of mates correlate d highly significantly, implying that high-ranking birds were paired w ith other high-ranking birds and low-ranking birds with other low-rank ing birds. Birds of different age and sex did not show any differences in the proportion of initiated aggressive encounters directed at othe r individuals, However, males were more aggressive to other males than to females and also tended to behave less aggressively towards their own mates than towards other individuals in the flock. This could be a male strategy to strengthen the pair-bond and to enhance mate protect ion described earlier in the Willow Tit.