Plumage Variation and Sex Ratio in the Brown-Backed Parrotlet (Touit melanonotus; Psittacidae)

The Brown-backed Parrotlet, Touit melanonotus, is a rare endemic bird to the Brazilian Atlantic Forest, currently considered as “Vulnerable” in the Brazilian Red List of Threatened Species. We estimated the sex ratio of a wild flock of T. melanonotus using molecular markers, examined morphological variation in 34 museum specimens to test for sexual dimorphism, and conducted a literature review about sex ratio in Psittacidae for comparative purposes. We found a sex ratio of 0.8:1 (male/female; n = 29) in T. melanonotus, and a χ2 Goodness-of-fit test showed no significant difference from equality (p > 0.05). We describe three main categories in plumage: the first (and most common) comprises uniformly lime green birds, slightly darker on the head. The second is composed of individuals who are overall lighter, with the breast feathers washed with light greenish gray, and feathers of the head being dark lime green, presenting a sharp contrast with the breast feathers. The third and the rarest one is composed of birds with light greenish gray underparts with emerald green and darker upper parts. T. melanonotus has no apparent sexual dimorphism. We found no evidence of geographic variation. Sex ratio deviation may not be a parameter increasing the vulnerability of the species. Data like these represent a big leap in the knowledge of the species and has the potential to help and inform conservation efforts.