Only one species of Houbara? A response to Cowan

The classic test under the Biological Species Concept of whether two closely related taxa are conspecific is to see what happens when they come into contact – do they interbreed and produce fertile offspring or not? If they
never come into contact, however, the test is not possible and the issue has to be settled by other means. The Houbara Bustard (African Houbara) Chlamydotis undulata and Macqueen’s Bustard (Asian Houbara) C. macqueenii
represent one such case, separated by the Nile and its human settlements and
never, to anyone’s knowledge, geographically in contact, although in the recent past they may have been as close as 100 km (Gaucher
et al. 1996), and in more distant eras, when their populations were presumably much larger and habitat more nearly continuous (the Nile is no barrier), one might have expected perhaps quite frequent overlap of wandering birds in Egypt’s easternmost Western Desert and northernmost Eastern Desert.