Barbary Falcon - Taxonomy

Taxonomy

The Barbary Falcon differ in appearance from the Peregrine Falcon according to Gloger's Rule. The genetic distance is slight and the species form a close-knit and somewhat paraphyletic group in DNA sequence analyses. They differ more in behavior, ecology and anatomy than usual for conspecifics. They are able to produce fertile hybrids, but they are generally allopatric and only co-occur during breeding season in small areas such as the Maghreb, the Punjab, Khorasan, and possibly the Mongolian Altai, and there is clear evidence of assortative mating with hybridization hardly ever occurring under natural conditions. In short, though they occupy adjacent territories, they breed at different times of year and Barbary Falcons virtually never breed with Peregrines in nature.

Assuming a genetic distance of 2% in hierofalcons corresponds to a divergence roughly 200,000-130,000 years ago, the 0.6-0.7% genetic distance in the Peregine-Barbary Falcon ("peregrinoid") complex suggests its current taxa evolved in the Late Pleistocene some 100,000 years ago or less, but before the Upper Paleolithic. The presumed time of divergence between Peregrine and Barbary Falcons approximately coincides with the start of the last ice age, when desertification was prominent in North Africa and the Middle East, and the Persian Gulf became a landlocked inland sea that slowly dried up. Populations of ancestral "peregrinoid" falcons living in marginal habitat at the fringe of the African-Middle Eastern desert belt either adapted (and might have become isolated e.g. in the Persian Gulf region, which turned into semiarid habitat surrounded by vast deserts), or left for better habitat, or became extinct. During interstadials, deserts receded and the aridland and humidland populations could expand to contact again, causing some limited gene flow. This scenario by and large parallels the proposed evolutionary history of the Saker Falcon in relation to the other hierofalcons; indeed, that group shows similar patterns of molecular paraphyly though it is of somewhat earlier origin.

The fossil record adds little to the issue. A humerus some 9,000 years old (i.e., after the last ice age) from the Aswan area in Sudan, where Falco peregrinus minor occurs today, was identified to belong to the Peregrine. The Barbary Falcon is one of the rare cases that may arguably be considered a species under the Biological, but certainly not under the Phylogenetic Species Concept rather than the other way around as usual. This case demonstrates that what makes a "species" is not only its descent, but also occurs to a population in the course of evolution, how it adapts, and how this affects its reproductive isolation (or lack thereof) from sister taxa.