Year-round molt pattern, body condition and ectoparasitism in the Blue-black Grassquit (Volatinia jacarina)

Abstract

Understanding how tropical birds organize energetically demanding activities such as molting, breeding, and migration is central to the study of avian life-history strategies. Despite the remarkable diversity of Neotropical species, information on their annual cycles remains scarce. Here, we investigated the temporal pattern of molting and its relationship with body condition and ectoparasite infestation in the Blue-black Grassquit (Volatinia jacarina), a socially monogamous, granivorous passerine from central Brazil. Molting was not randomly distributed but exhibited a clear bimodal pattern, with peaks during the dry season and the rainy season. Both body and flight feathers were replaced during the same periods, and no sexual differences in molting timing were detected. Chewing lice infested 47.5% of individuals, with abundance increasing during both the breeding and molting periods, yet without measurable effects on body condition. Individuals molting during the rainy season were in better condition than those molting in the dry season or not molting at all, likely reflecting higher food availability and the influence of environmental seasonality. Our findings reveal that grassquits face overlapping energetic challenges across its annual cycle, suggesting limited flexibility in scheduling molt relative to other life-history events. These results contribute to filling a major gap in our knowledge of annual-cycle dynamics in Neotropical birds and underscore the need for integrative studies linking molt, reproduction, and movement across variable tropical environments.