Journal of Field Ornithology (Sep 2022)
Replacement of rectrices by wintering White Wagtails: an experiment to examine effects of sex, age, and body condition
Abstract
Adventitious replacement is regrowth of accidentally lost feathers outside usual molt periods. To examine the intrinsic factors affecting adventitious replacement, I conducted feather-plucking experiments on White Wagtail (Motacilla alba lugens) during the coldest time of the year. I examined sex, age class, and body condition of wagtails as potential factors affecting the ratio of the lengths of regrown rectrices (T4) to their original lengths. I captured and ringed 288 wagtails in January, plucked and measured the length of the right T4, and measured tarsus length and mass. I recaptured 121 of the wagtails approximately 6 weeks later, and plucked and measured their regrown T4s. In a modeling analysis of the ratio of original to fully grown T4, males regrew their T4s to lengths closer to those of their original T4s than did females. Males are presumed to need longer tail feathers than females. Differences in regrowth were not explained by age class. Both adults and yearlings must acquire sufficiently long rectrices for them to achieve full their functionality significance. Individuals in better condition tended to regrow their T4s to lengths closer to those of their original T4s than did individuals in poorer condition. Adventitious replacement may be influenced by body condition in those individuals that finished regrowing their rectrices early. In an analysis of the ratio of original to regrowing T4, the ratio for adults was greater than that for yearlings. Yearlings may be slower than adults to fill the gap left by losing a T4, or juveniles may have begun regrowth of their plucked T4s later than adults. Sex and body condition did not significantly contribute to the model. Because age-class difference in the regrowth speed of T4s might not be influenced by body condition, adventitious replacement is worthy of careful examination in the future in the context of life history strategies.
