Biometry and body weight of two sympatric Myiozetetes in an urban area of southwestern Brazilian Amazonia

While they present some variation in plumage, the species Myiozetetes cayanensis and Myiozetetes similis share many traits that can hamper their reliable identification, especially in the case of the juveniles. The present study investigated possible differences in the morphometry of the two species, found on the campus of the Federal University of Acre and the adjoining Zoobotanical Park in Rio Branco, Acre, Brazil. The campus is covered in grassy vegetation with some trees, while the park is a 160-ha fragment of secondary forest at varying stages of regeneration. Artificial ponds are found in both areas. Wing Length (WL) and Total Length (TL) were measured with a ruler, and the tarsus (T) with a calliper, while the birds were weighed (W) with a precision balance. We used the Mann-Whitney test to compare datasets. The birds were captured in 36 mm mesh mist-nets (12 m x 2 m) between 2010 and 2016. Overall, 38 adult Myiozetetes cayanensis and 39 adult Myiozetetes similes were measured. The results for Myiozetetes cayanensis were WL= 88.8±3.84 mm, TL = 177.4±6.91 mm, T=17.6±2.93 mm, W=27.5±2.95 g, and those for Myiozetetes similes were WL=89.1± 5.56 mm, TL= 178.4±8.10 mm, T=17.8± 2.36 mm, W=31.1±2.96 g. Only the weights varied significantly (P<0.001) between species. These results indicate that morphometry is not a useful criterion for the differentiation of the two species.