White-bellied Tyrannulet is lumped into White-crested Tyrannulet. Genetic divergence between the two groups is rather shallow (Rheindt et al. 2008, Harvey et al. 2020), and they exhibit little or no variation in vocalizations (Straneck 1993, Krabbe 2015, Pearman and Areta 2021). We continue to recognize each of the former species as separate groups: White-crested Tyrannulet (Sulphur-bellied) Serpophaga subcristata subcristata/straminea, with subspecies subcristata and straminea; and a monotypic goup White-crested Tyrannulet (White-bellied) Serpophaga subcristata munda.