Nest, eggs, and nestlings of the Gray-headed Tanager (Eucometis penicillata albicollis) from São Paulo State, Brazil

Abstract

The Gray-headed Tanager (Eucometis penicillata) has 7 subspecies widely distributed in Central and South America. Scattered reproductive data are available for most of them, but reproductive aspects were thoroughly documented only for E. p. stictothorax, from Costa Rica. Here, we provide detailed descriptions of nests, eggs, and nestlings of E. p. albicollis from southeastern Brazil, and compile nesting information available from this and other subspecies from the literature. During the 2019–2020 and 2020–2021 breeding seasons, we found 4 nests that were active from October to January. Nests were deep cups with 8.5–11.1 cm in outer diameter, constructed of loosely attached dry fibers and sticks, and could be supported at their rims, laterally, or from beneath. They were built in riparian forest understory, 1.1–1.5 m above ground, 1.0–10.5 m away from forest streams, and 72–100 m from the forest edge. Clutches consisted of 3 eggs. Eggs were brownish-gray in background color, with dark-brown blotches, measured 21.9 mm (±0.8) in length and 16.2 mm (±0.7) in width, and weighed 3.0 g (±0.3). The hatchlings had reddish skin, bright orange mouth lining, and white commissure. The pair shared nestling provisioning and we also document the first case of brood parasitism by Shiny Cowbird (Molothrus bonariensis) for the Gray-headed Tanager. Upon comparing our data with that of other subspecies, we observed differences in nest material, breeding phenology, clutch size, and eggs and nestling characteristics, which could be attributed to local adaptations of geographically distinct subspecies or to phylogenetic divergences between still unsplit species.