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

Abstract

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.

Factors influencing the evolution of moult in the non-breeding season: insights from the family Motacillidae

“…Moult is the process that allows the maintenance and adjustment of plumage functionality throughout the annual cycle (Jenni & Winkler, 1994). A high amount of variability in moult strategy within and among species (Svensson, 1992;Pyle, 1997a, b) is achieved through many elements that integrate a species' moult strategy (Barta et al, 2006): topography (the spatial configuration of the replaced feathers after a moult; Guallar et al, 2014), energetic requirements, feather quality, number and timing of moults per cycle, intensity, duration and order of replacement. Moult strategies may affect survival and fitness (Holmgren & Hedenstr€ om, 1995), and have probably evolved in response to shifts in natu-ral history and environmental parameters (Rohwer et al, 2009;Pap et al, 2015).…”

Partial or complete? The evolution of post‐juvenile moult strategies in passerine birds

“…(d) Length of the nestling period (in days, N = 860 species), collated from the Handbook of the Birds of the World (HBW; del Hoyo et al, 2018) and Cooney et al. (2020). (e) Habitat openness ( N = 1,311 species).…”

Defining moults in migratory birds: a sequence‐based approach

“…Among upperwing secondary coverts, feathers are generally replaced in a distal direction among each tract (marginal, median and greater coverts) during preformative moults, as implied by most resultant moult phenologies (Guallar and Jovani 2020a, b), whereby most or all formative feathers are located proximal to most or all juvenile feathers, defining moult limits following partial replacement (Pyle 1997, Jenni and Winkler 2020). Although exceptions and some variation in covert‐replacement phenologies can occur between and occasionally within species (Pyle 1997, Guallar et al 2014, Guallar and Jovani 2020b, Jenni and Winkler 2020), in most cases a prevailing order to feather replacement appears to be maintained. Prealternate moults may involve different replacement mechanisms, as feather‐replacement sequences can vary to a greater extent than those of prebasic and preformative moults, e.g.…”