DEVELOPMENT OF FLUCTUATING ASYMMETRY IN TAIL FEATHERS OF THE BARN SWALLOW HIRUNDO-RUSTICA

Fluctuating asymmetry represents usually small, random deviations from symmetry in bilateral morphological characters. The ontogeny of asymm etry in morphological characters may reveal information about developm ental processes in a general sense. I studied the development of fluct uating asymmetry in feather characters of the barn swallow Hirundo rus tica, that are developed repeatedly during the single annual moult, wi th the following results. First, the side developing a larger feather was found to be partially biased, as demonstrated by one side consiste ntly developing a larger feather under natural and experimentally indu ced growth episode events. Second, asymmetric feathers were found to c onsist of asymmetric daily growth increments, and the size of the incr ements developing under different environmental conditions were positi vely correlated. Third, fluctuating asymmetries of feathers developing under different environmental conditions were positively correlated, although the level of asymmetry was larger under adverse environmental conditions. Fourth, individual asymmetries in tail length and growth bar length were unrelated to the duration of the developmental period, although late growth increments were smaller and more symmetric than early increments. These observations suggest that fluctuating asymmetr y partially arises as a consequence of a random bias in the feather fo llicles and differences in environmental conditions during ontogeny of feathers.