Winter Floaters in Willow Tits Parus Montanus a Matter of Choice or Making the Best of a Bad Situation?

Abstract

Winter flocks of Parus species are formed during summer and early autumn as dispersing juvenile tits often settle with an adult mated pair that already occupy an exclusive year-round territory (see Hogstad 1989a). Such flocks often have a constant membership with individuals organized in a linear dominance hierarchy. As a consequence of adult occupancy of territories and social dominance, juveniles that become established as flock members generally become subordinates within each sex. Although flock formation usually takes place during July and August, movement of unsettled juveniles may continue into autumn (Smith 1976, 1984, Ekman 1979a,b, Weise and Meyer 1979, Ekman et al. 1981, Hogstad 1989b). These non-territorial birds, or winter floaters, can be characterized as individuals that wander among flocks or territories without settling. Since only flock members seem to achieve reproductive status the following spring (Ekman 1988, Hogstad 1989b), a crucial question arises: why be a winter floater? Is the wandering behaviour a strategy preferred by some birds, or are they forced to be floaters simply because the area is saturated bv dominant conspecifics?