Splendid isolation: historical ecology of the South American passerine fauna

A few years ago, I had my first opportunity to visit the Amazonian Basin in eastern Ecuador. Several days of mist-netting and birding within an intact forest and in surrounding disturbed habitats turned out to be a pivotal experience, finally crystallizing in my mind a pattern that every Neotropical ornithologist knows but whose significance has largely escaped us. I am referring to the fact that most of the birds of the forest understory belong to the large South American endemic radiation of songbirds, the suboscines, called the infraorder Tyrannides (suborder Tyranni) by Sibley and Ahlquist (1990). This clade includes the ovenbirds, woodcreepers, antbirds, manakins, cotingas, and flycatchers, among others. Birds more familiar to North Americans, the oscine passerines (suborder Passeri), including the New World orioles, tanagers, and emberizine finches, dominate the forest canopy and habitats outside the forest, along with a few species-rich clades of tyrannine flycatchers (family Tyrannidae, subfamily Tyranninae). South America was an isolated island continent