He suggested that the different species evolved from one common ancestor whose population was fragmented by the retreat of the rainforest into the wettest areas during periods of dry climate in the Pleistocene epoch.

In any case it is simply one of several competing hypotheses to explain Amazonian biodiversity, each of which may or may not provide a good explanation for the geographical pattern found in any one group of taxa.

In the present case, the refugia hypothesis is probably correct, as the Amazonian Selenidera have distributions centered on major river systems; they might be considered a superspecies.

Some other birds from the region, in contrast, have sister species that are separated by the major rivers, which thus apparently acted as natural barriers to gene flow.

Whether a refugia or a barrier model describes superspecies distribution in the Amazonian basin most appropriately thus seems to be a direct consequence of the animals' ability to cross major waterways.