Merlin (bird) - Systematics

Systematics

The relationships of the Merlin are not resolved to satisfaction. In size, shape and coloration, it is fairly distinct among living falcons. The Red-necked Falcon is sometimes considered more closely related to the Merlin than other falcons, but this seems to be a coincidence due to similar hunting habits; it could not be confirmed in more recent studies. Indeed, the Merlin seems to represent a lineage distinct from other living falcons since at least the Early Pleistocene, some 5 Ma (million years ago). As suggested by biogeography and DNA sequence data, it might be part of an ancient non-monophyletic radiation of Falcos from Europe to North America, alongside the ancestors of forms such as the American Kestrel (F. sparvierus), and the Aplomado Falcon (F. femoralis) and its relatives. A relationship with the Red-necked Falcon (F. chicquera) was once proposed based on their phenetic similarity, but this is not considered likely today.

In that regard, it is interesting to note a fossil falcon from the Early Blancan (4.3–4.8 Ma) Rexroad Formation of Kansas. Known from an almost complete right coracoid (specimen UMMP V29107) and some tarsometatarsus, tibiotarsus and humerus pieces (V27159, V57508-V57510, V57513-V57514), this prehistoric falcon was slightly smaller than a Merlin and apparently a bit more stout-footed, but otherwise quite similar. It was part of the Fox Canyon and Rexroad Local Faunas, and may have been the ancestor of the living Merlins or its close relative. With its age quite certainly pre-dating the split between the Eurasian and North American Merlins, it agrees with the idea of the Merlin lineage originating in North America, or rather the colonization thereof. After adapting to its ecological niche, ancient Merlins would have spread to Eurasia again, with gene flow being interrupted as the Beringia and Greenland regions became icebound in the Quaternary glaciation.