Moult topography and its application to the study of partial wing‐moult in two neotropical wrens

During partial moults birds replace a variable number or percentage of old feathers. This quantity, known as moult extent, has been a primary variable used in comparative studies. However, different spatial configurations of feather replacement may result from an equal number of renewed feathers. Few studies have addressed spatial aspects of moult, which may vary among species, among individuals of the same species and between episodes at the individual level. We present a novel approach to quantify the spatial configuration of a wing-moult episode, hereafter referred to as moult topography, which comprises two elements, namely extent and vector, the latter condensing the spatial configuration of the replaced feathers on the wing plane. We apply this method to investigate preformative (post-juvenile) wing-feather moult pattern in the Spot-breasted Wren Pheugopedius maculipectus and the White-breasted Wood-Wren Henicorhina leucosticta. We specified a null model of wing-moult topography by which feather replacement follows a discrete anterior-posterior (vertical) axis between tracts and a discrete proximal-distal (horizontal) axis within tracts, and whereby wing feathers from a new tract are replaced only if all the feathers from the previous (anterior) tract have been replaced. Our sample of Spot-breasted Wrens showed a strict single pattern of replacement that did not differ significantly from the null model. Our sample of White-breasted Wood-Wrens, however, differed significantly from the null model, showing prioritization of proximal wing feathers closer to the body. These differences might have biological relevance, for example in mate selection or in response to different environmental stressors, and might reveal the influence of these factors on the evolution of moult strategies. Overall, moult topography provides a new approach to future ecological and evolutionary studies of moult.