Left: Blue-winged warbler | Right: Golden-winged warblerLeft: © istock.com/BirdImages; Right: © Jayne Gulbrand/Shutterstock.com
What defines a species? Because the boundaries between species can appear so fluid, pursuing such a question seems, at times, like academic esoterica—little different than discussing how many angels can dance on the head of a pin. But accurate species definitions lie at the heart of biological investigations and management of natural resources (e.g., the US Endangered Species Act). It is troublesome, therefore, that new information on the genetic structure of long-recognized species of birds could jeopardize their status as full species.
The problem, in a nutshell, is that the DNA of many familiar species of birds holds signatures of substantial exchange of nuclear genes with other bird species. Such gene exchange matters because, by decades-old definitions, it is the isolation of gene pools that ...
