Nesting biology of the plain-throated Antwren (Isleria hauxwelli): an antbird with exceptional life history traits

Abstract

Isleria is a recently described genus in the Neotropical family of antbirds (Thamnophilidae), comprising two species that inhabit the Amazon basin from Colombia to Brazil. Little is known about the breeding aspects of this genus. We present a detailed description of the nest, eggs, nestlings, and parental behaviour of the Plain-throated Antwren (Isleria hauxwelli), based on ten nests monitored in a lowland tropical forest located in Manu National Park, Peru. The nest is a suspended open-cup shaped structure containing two dark maroon spotted eggs, which measured 18.51 ± 0.96 × 13.27 ± 0.47 mm and weighed 1.71 ± 0.2 g (n = 16). The incubation period lasted 21 days and nestling period extended for 10 days. Both parents attended the nest, providing an overall daily nest attentiveness of 52.62%. Both females and males incubated the eggs, brooded, and fed the nestlings, but males and females showed differences in the frequency of these parental-care behaviours. The relatively long incubation period, along with an extremely short nestling period and a low nest attentiveness fall in the extremes of breeding and life-history strategies for antbirds, in particular, and for Neotropical birds in general. Finally, the nest architecture of Isleria hauxwelli adds to the morphological, behavioural, and ecological differences with its sister group, Thamnomanes, reinforcing the recognition of the new genus, Isleria. Our results emphasise the importance of incorporating natural history information into evolutionary and ecological questions.