Strained energy budget of winter floaters in the Willow Tit as indicated by ptilochronology

Most Willow Tits Parus montanus live within flock territories during the non-breeding season, but many juveniles roam around or switch between several flocks. Such floaters behave submissively and spend time watching other flock members in addition to scanning for predators. During September–December 1989–2000, I studied individually colour-ringed Willow Tits living in a subalpine forest area in central Norway. When among flock members, the floaters foraged less in favourable parts of trees and were more vigilant than the lowest-ranked juvenile flock members. The nutritional condition of the birds was assessed by examining the growth bar widths of their tail feathers. Birds in better condition have wider growth bars than those in poorer condition. The daily growth bars of induced feathers of male and female floaters, laid down under winter conditions, were significantly narrower than those of the lowest ranked flock members. These results suggest that juvenile floater Willow Tits maintain a poorer nutritional status than low-ranking juvenile flock members during winter.