Feather development under environmental stress:: lead exposure effects on growth patterns in Great Tits Parus major

Capsule Regrowth rate of tail feathers is more strongly affected compared to feather length and symmetry. Aims To assess the value of avian feathers as bioindicators. Methods The origin and persistence of fluctuating asymmetry (FA) in homologous pairs of regrowing feathers was studied in captive birds under different levels of environmental stress, respresented by exposure to lead (Pb). Homologous feathers of individually housed birds were plucked synchronously or with a delay of seven days. We measured growth rate, regeneration time, final size and FA of regrown feathers and related them to Pb stress. Results Asymmetry decreased as feathers reached their final length. This was not due to compensatory growth but rather a consequence of the programmed growth trajectory of single feathers. Tail feathers grown under higher Pb pollution showed increased regeneration times, decreased growth rates and shorter lengths, but no changes in development times nor in FA. For differences between both (i) original and induced feathers and (ii) control and Pb treatment, effect sizes of parameters related to feather development (growth bar width, growth rate, regeneration and development time) were consistently larger than those related to the resulting phenotype (feather length and FA). Conclusions Growth bar widths in particular provide an applicable, sensitive and reliable indicator of adverse conditions such as Pb pollution and experimental conditions. In general, phenotypic characteristics that retrospectively allow estimation of growth rates may be more suitable for monitoring environmental stress than sizes or asymmetries of full-grown traits.